DOS Times - DOS Times - Vol 26 No. 3

DVolume 26, No. 3 SNovember-December 2020 For Private Ciruculation Only
TIMES

HighlighLtosrem ipsum
Refraction and
Spectacle Prescription
Issue

Aspects of Spectacle Dispensing

Telehealth and Refraction and
Co-Management

Drugs in Refraction

Special Conditions in Refraction

Consensus Statement for
Strengthening Refractive Error
and Presbyopia Services in
India. Objective and subjective
Refraction

Official Bulletin Magazine of

DELHI
OPHTHALMOLOGICAL
SOCIETY

Contents 36 Objective Refraction - A Clinical Perspective
39 Refraction in a Visually Impaired Person
Editorial 43 Subjective Refraction
46 Telehealth, Refraction and
05 Prof. (Dr.) Namrata Sharma
Hony. General Secretary Co - Management
49 Progressive Lens ……. A Boon for Presbyopes
06 Prof. Subhash Dadeya 53 Ametropia - Optical Considerations for CL
President
Wear
07 Prof Monica Chaudhry 55 Refraction in Accommodation and

Subspecialities Convergence Anomalies - Case Studies
Refraction and Spectacle Prescription 57 Difficult Situations in Refraction
63 Refraction and Binocular Balance of
08 Aspects of Spectacle Dispensing
12 Artificial Intelligence and Eye Accommodation
15 All you need to know about Visual Acuity 65 Rapid Objective Refraction technique in

Assessment with Snellen and LogMAR Charts babies
19 Ametropias Emanating from 67 Refraction in Keratoconus

Emmetropization DOS Quiz
22 Consensus Statement for Strengthening
83
Refractive Error and Presbyopia Services in
India Tearsheet
27 Understanding Contrast Sensitivity
Measurement and its importance 86 Sharpen your Refraction Knowledge
31 Drugs used in Refraction

DOS Executive Members 2019-21

DOS Office Bearers

Dr. Subhash C Dadeya Dr. Pawan Goyal Dr. Namrata Sharma Dr. Hardeep Singh
President Vice President Secretary Joint Secretary

Dr. Jatinder S Bhalla Dr. Vinod Kumar Dr. Manav Deep Singh
Treasurer Editor Library Officer

Executive Members

Dr. Dewang Angmo Dr. Jatinder Bali Dr. Shantanu Gupta Dr. C. P. Khandelwal

Dr. Rahul Mayor Dr. Vipul Nayar Dr. Rajendra Prasad Dr. Kirti Singh

DOS Representative to AIOS Ex-Officio Members

Dr. Jeewan S. Titiyal Dr. M. Vanathi Dr. Rakesh Mahajan Dr. Arun Baweja

www.dosonline.org/dos-times DOS Times - Volume 26, Number 3, November-December 2020 03

Volume 26 No. 3, November-December, 2020

DOS Times Editorial Board

Editor In Chief Editorial Board National Board
Namrata Sharma
Dr. Atul Kumar Dr. Parul Icchpujani
Editor Dr. Aniruddha Maiti Dr. Ronnie George
Prafulla Kumar Maharana Dr. Apporva Ayachit Dr. Sushmita Kaushik
Dr. Jitendra Jethani Dr. Gopal Pillai
Assistant Editors Dr. Mita Joshi Dr. Usha Singh
Dr. P. Dutta Majumdar Dr. Subhendu Boral
Dr. Noopur Gupta Dr. Meena Chakrabarti
Dr. Brijesh Kakkar Dr. Raksha Rao
Dr. Digvijay Singh Dr. Kumudini Verma
Dr. Ritika Sachdev Dr. Rashmin Gandhi
Dr. Dewang Angmo Dr. Siddharth Kesarwani
Dr. Rebika Dr. Chaitra Jayadev
Dr. Saurabh Sawhney Dr. Bibhuti P. Sinha
Dr. Reena Sharma Dr. Amit Porwal
Dr. Rajat Jain Dr. Prashant Bawankule
Dr. Jaya Gupta Dr. Arvind Kumar Morya
Dr. Anita Ganger
Ritu Nagpal Sahil Agarwal Dr. Umang Mathur
Dr. Neera Agarwal
Gunjan Saluja Deepali Singhal Dr. Poonam Jain
Dr. Manisha Agarwal
Dr. Hardeep Singh
Dr. Anita Sethi
Dr. Tushar Agarwal
Dr. Rohit Saxena
Dr. Swati Phuljhele
Dr. Vivek Dave
Dr. Mohita Sharma
Dr. Rajesh Sinha
Dr. Ritu Arora
Dr. P.K. Pandey
Dr. H.K. Yaduvanshi
Dr. O.P. Anand

Mohamed Ibrahime Asif Rahul Kumar Bafna

Sohini Mandal Prakhyat Roop

Editorial

From the
Editor Desk

Prof. (Dr.) Namrata Sharma Dear Members,

(MD, DNB, MNAMS) Uncorrected refractive errors are by far the commonest cause of poor vision, more
so in school going children .
Hony. General Secretary
Delhi Ophthalmological Society The diagnosis and rehabilitation of patients with uncorrected refractive errors
and low vision has probably added as much to the quality of life and extended its
Cornea, Cataract & Refractive Surgery Services usefulness as any advance in the biological sciences.
Dr. R.P. Centre for Ophthalmic Sciences,
All India Institute of Medical Sciences (AIIMS) The various article in the text cover the spectrum from basic objective and
New Delhi subjective refraction, to convoluted refraction techniques used in visually
impaired patients, accommodation and convergence anomalies, ectatic corneal
conditions like keratoconus and paediatric refractive errors as well, which are so
difficult to address even in experienced hands .

In a comprehensive eye examination, there are several steps and procedures,
every step needs to be in coherence for the better understanding of the refractive
status of eye.

From visual acuity assessment, where LogMAR chart provide more accurate
assessment compared to conventional charts like Snellen chart and contrast
sensitivity is also important : all aspects have been discussed. Apart from
the objective an subjective refraction, the ametropias emanating from
emmetropization and the use of artificial intelligence in the refraction has also
been discussed. The art of dispensing spectacles, especially progressive lens
in presbyopes, after taking into account the personal lifestyle and vocational
needs of the patients, is something which is not easy to master which has been
highlighted. Further the drugs used for refraction to cause cycloplegia have been
highlighted along with contact lens rehabilitation.

I hope that the practical information provided in this DOS Times will go a long
way in improving the standard and quality of refraction and this will give a concise
understanding for not only the optometrists ,post graduate students but also the
general ophthalmologists who wish to enhance and refresh their knowledge in
this field .

Prof. (Dr.) Namrata Sharma
Hony. General Secretary

www.dosonline.org/dos-times DOS Times - Volume 26, Number 3, November-December 2020 05

President’s Editorial

From the
President’s Desk

Dear Friends and Colleagues,

We are pleased to write another exciting issue of DOS Times, which has a special focus
on prescription of glasses, Refractive Errors, Presbyopia, contrast sensitivity and artificial
intelligence.

As a resident and General Ophthalmologists, we expect all of you to be through through one
topic that is accurate prescription of glasses.

Uncorrected refractive error are second most common cause of blindness. As on date

uncorrected myopia and presbyopia are major challenging situations. Loss of employment

and educational opportunities and social stigmas are some of the impacts of uncorrected

refractive errors. Prof. Subhash C Dadeya

Visual impairment is one of the major health care problems, long hours of studies, excessive President

near work, Excessive use of screen and less outplay activities play a major role in development

of myopia. The challenging situation can be tackled by training optometrists, delivering refractive care services through mobile

vans ,school screening and comprehensive eye care services.

Prescription of Spects is an art. Accurate prescription is key to success and doing final verification before prescribing is always
better. There is no shortcut or substitute to accurate prescription of glasses.

Early detection and prevention of progression of myopia by using low dose Atropine, ortho -K and multifocal contact lenses
and treating with Spects, contact lenses and refractive surgery are key to success.

Treating a presbyopia is a Wishdream for all of us.

Spectacle correction, contact lenses ,monovision correction, corneal refractive procedures and medical treatment are some of
the treatment modalities for presbyopia.

I would like to congratulate the editorial team and our dynamic Secretary Prof Namrata Sharma for bringing out this excellent
issue of topic of utmost importance.

I would like to thank each one of you for making the Mid term DOS conference and international DOS conference on Virtual
platform a grand success. I welcome to each one of you to our upcoming Annual DOS conference

This Executive is completing its term and DOS will be holding elections for various posts.

Free and fair elections are essential for the growth of any democratic organization. It is the duty of each one of us to participate
in elections and ensure free and fair elections.

Wish each one of you a pleasant reading.

Prof. Subhash Dadeya
President, DOS

06 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Guest Editorial

Guest
Editorial Desk

Respected DOS members,

Sometimes all you need is a good Refraction.

Refraction is the core of an optometrist’s/ ophthalmic assistants routine work, but the outcome of
the refraction impacts the decision for management of patients. It is informed ophthalmologist
that an extract vital finding in patient care from the refractionist. Unfortunately, in many examples
they cannot relate the eye and its management in totality. Prescribing guidelines are the key even
after a decent refraction.

The techniques remain to be our old-fashioned retinoscope and fundamental subjective principles, Prof Monica Chaudhry
optics and nothing has changed much except for more addiction to Autorefractors. The trend in

recent innovations is in telemedicine and Artificial intelligence supplement in refraction techniques. This is anticipated to be

the forthcoming and certainly will progress to better and newer cleverer techniques. Although the retinoscope is less used an

AR is dominant, yet so far, its distinctive use is irreplaceable. The visual acuity trend is to include Log MAR charts and contrast

acuity charts in the clinic.

The subjective testing requires no less than 20 minutes and is the standard practice to run it monocularly without end point of
binocular balancing. Refraction cabin should include tools like Duochrome chart, cross cylinder, contrast chart, LogMAR charts
Hallberg clips, opticians scale etc. These are typically not found across refraction cabins. Phoropters are helpful but luxurious
for Indian system.Interpretation of accommodation and convergence of the eye during refraction is essential and unless that
is comprehended, patient satisfaction is questionable. Correct choice of Cycloplegia is the crucial for any refraction and this
edition highlights the fundamentals.

Having basic knowledge of the dispensing spectacle with best recommendation is critical to complete the good refraction.
Uncorrected refractive error and its community integration to resolve the problem needs to be considered which regrettably is
one of the major leading cause of visual impairment.

This special edition brings in basics for performing most of the effective refractive techniques by experienced optometrists. It
presents individualised special conditions and approaches for these special conditions. The aim is to assemble the understanding
of an ophthalmologist trainee and practicing ophthalmologist in the subject of refraction. Experienced practitioners can use it
to revise their own approach to the care of patients.

The issue is a collective effort of expert’s Dr Anitha Arvind, Dr Sumit Grover, Nilesh Thite, Md. Oliullah Abdal who have
been unbelievably valuable in identifying professionals and reviewing articles with me. I them instead of you for the dedication
and wish all authors on this issue success.

Above all I would like to thank the DOS who believed in updating the concept refraction and favoured me in bringing up this
issue.

Prof Monica Chaudhry

B.Sc, Msc Optometry, FIACLE Consultant Optometrist and educator
Founder Learn Beyond Vision
Advisor, Adjunct professor GD Goenka University
Retd. Optometrist and educator AIIMS
Sr Consultant IGNOU, Prof and HOD optometry, Amity University
Ex Director Sushant University School of Health Sciences

www.dosonline.org/dos-times DOS Times - Volume 26, Number 3, November-December 2020 07

Subspeciality - Refraction and Spectacle Prescription

Aspects of Spectacle Dispensing

Anitha Arvind B.S (Opt), M.Optom, PhD, FIACLE, FBDO (o/s), FASCO (VT)
Consultant Optometrist & Optometry educator
Eye Care Centre, Bangalore

The art of spectacle dispensing involves providing advice and supply the most comfortable fitting and
aesthetically appealing spectacles after taking into account the personal visual, lifestyle and vocational needs
of the consumer. It also includes the interpretation of the prescription and recommendation of lenses, tints
and coatings to provide optimal visual performance, combined with suitable spectacle frames to ensure a
comfortable fit. The ultimate goal of spectacle dispensing is to make the wearer ‘Look, Feel and see Better’.

Maximising spectacle lens 2. Refractive index: Higher the The table 1 below shows the central
appearance refractive index thinner the lens. thickness comparison of plus lenses
Also high index lenses have and how blank size selection matters
The factors which influence the smaller sags so they appear flatter.
appearance of a spectacle lens include: Refractive index of spectacle lenses Table 1: Central thickness comparison of
range between 1.5 to 1.9. High plus lenses with different blank sizes
- Lens form index lenses have low Abbe value
meaning higher dispersion or suffer Power 65mm 55mm 50mm
- Refractive index from higher Transverse Chromatic +2.00D 3.4mm 2.5mm 2.3mm
Aberration (TCA) which the wearer +4.00D 5.4mm 4.0mm 3.4mm
- Minimum Blank Size (MBS) complaints as colour fringes around +6.00D 7.3mm 5.5mm 4.5mm
light sources.
- Lens shape and thickness Tip: Always choose a minimum
3. Minimum Blank Size (MBS): blank size for minimum thickness of
- Anti reflection coating Choosing the correct blank size plus lens
plays a pivotal role in dictating the 4. Lens shape: Lens thickness is
1. Lens form: This describes both the thickness of the lens when glazed.
shape and thickness of a lens. Two Glazing in spectacle dispensing directly related to the size of the
basic lens forms are flat and curved. involves cutting and edging a lens finished lens. The preferred lens
The sag of a lens determines the to fit or mount in a spectacle frame. shapes are
maximum thickness of a lens for Minus lens can be made thinner by Round/Oval lens shape - Hyperopes
a patient. The base curve of a lens edging them to a reduced diameter Rectangle lens shape - Myopes
determines the final lens form for as the periphery of the lens is thicker
a desired lens power. For example while a plus lens whose centre is Role of frame shape in overall
a -5.00D lens can be made in flat thick cannot be made thinner by appearance of spectacles
form or curved form. Flat forms edging them to a reduced diameter.
for this lens prescription include So, order the smallest blank size to A narrow B size (vertical length of the
plano concave and biconcave while edge a plus lens for a thinner lens. frame) of the frame exposes thick edges
curved form means a meniscus lens Do not choose stock lenses for plus with high plus lenses (Figure 1)
made on a base curve. For example lenses dispense. The smallest blank
a -5.00D lens made on a +8.00BC size can be calculated using the A narrow B size of the frame resulting
will have +8.00D on one surface following formula: in thinner edges in high minus lenses
and -13.00D on the other surface in (Figure 2)
meniscus form. MBS = (Difference between patients
PD and BCD) + longest lens diameter +
How to determine the lens form? 2mm

A Geneva lens measure helps to
identify the form of the lens.

08 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

Figure 1: Plus lens Figure 3: Asymmetric decentration causing
unacceptable differences in lens thickness
Pic courtesy: www.opticianonline.com

Tip: When dealing with medium
to high prescriptions, 3mm
decentration per eye should be
considered maximum to maintain
cosmetic acceptability

5. Anti Reflection Coating (ARC):
The amount of light that is reflected
from the surface of a lens needs to
be considered when dispensing
spectacle lenses. Unacceptable
levels of loss are considered to occur
if there is reflectance of over 12%
of input light. An ARC is always
recommended when dispensing
a material of index 1.6 or above.
In addition ARC also helps to
minimise or eliminate ghost images
which trouble all spectacle wearers
of low and high powers.

Figure 2: Minus lens Simple dispensing
Figure 1 and Figure 2: Courtesy www.opticianonline.net Single Vision Lens dispensing

Centration of lens and its role It is also essential to ensure that The decision to choose the right lens is
in final lens thickness while dealing with medium and high governed by factors such as cosmetic
prescriptions a 3mm decentration per appearance, mechanics of using lenses,
The Box Centration Distance (BCD) eye should be considered maximum to the use to which the spectacles will be
or more commonly the frame PD maintain cosmetic acceptability. For put and any optical considerations as
should match the patients PD so that instance, if the above example of frame result of choice.
minimum or no decentration of lens is PD is chosen for a patient whose PD is
required. 66mm but monocular PDs are 30/36mm (I) For prescriptions below ±3.00D
the asymmetric Decentration may CR39 is the material of choice as it
BCD of Frame PD = A size of frame + cause unacceptable difference in lens
DBL (Distance between lenses) thickness, hence monocular PDs play is light in weight, has good scratch
an important role in frame selection as resistance properties with great
The A size and DBL are mentioned on well as final appearance of the spectacle optics and ease of tintability.
the temple of every frame lens in the frame. (II) For prescriptions above ±3.00D
The lens material and form need
Eg: 52/16 means the frame PD is 52+16 = The figure 3 shows how asymmetric to be decided as centre and edge
68mm and this frame would be suitable decentration can cause unacceptable thickness becomes important. For
for a wearer whose PD is more or less differences in lens thickness. plus lenses prefer aspheric lens
close to the frame PD. designs. Choose a higher refractive
index lens for minus lenses. The

www.dosonline.org/dos-times DOS Times - Volume 26, Number 3, November-December 2020 09

Subspeciality - Refraction and Spectacle Prescription

Abbe value determines the off- Progressive Addition Lens Important measurements for PAL
axis performance of a lens and can (PAL) dispense dispense
become annoying for wearers with
low Abbe values especially for PALs are lenses designed for presbyopes 1. Monocular PD measurement
those who are night driving. with power gradually increasing and fitting heights
from the distance zone, through a
Bifocal Lens dispensing progression to the near zone. Other The monocular PD (Pupillary
The factors that influence in deciding names for PALs are multifocals, distance) is the distance between
the right pair of bifocals are Progressive Power Lenses (PPLs) and the centre of the bridge of the nose
varifocals. PALS provide uninterrupted and the pupil centre/margin (Figure
• Field of view in either lens area vision for all distnaces with no visible 4) and can be measured using a
• Range of vision through either lens dividing line making it cosmetically simple millimetre ruler, PD rulers
superior to bifocals. The change in or the more popular pupillometer.
area front surface curvature required for The fitting height (Figure 4) is the
• Cosmetic appearance progressive surface results in surface distance from the pupil centre to the
• Optics and mechanics of use astigmatism. These blended zones bottom of the lens. Sophisticated
• Physical comfort of spectacles provide blurred vision and unusable. instruments are available from
PALs are designed so that these zones several manufacturers to take
Bifocal spectacles fulfil the needs of of poor vision are pushed out of line design specific measurements
a presbyope for his distance and near of sight. There are several PAL designs and customize the PAL lens fit.
vision. Various bifocal segment designs available currently each finding its own The minimum fitting height
are available each having its own merits use. Understanding the needs of the requirement is specified for each
and demerits. Table 2 highlights the wearer as well as task analysis help in PAL design by the manufacturer in
field of vision, cosmetic appearance, placing recommendations for the right the fitting guide. The chosen frame
jump effect and effect of prism in near PAL design. Fitting of the PAL lenses with the fitting height markings
due to main lens in various bifocal correctly ensures maximum benefit has to be placed on the product
segment lens designs. from their design. specific layout chart to ensure that
no seeing portions of the lens are
Table 2: Bifical types and their effects cut off when fitting the lens into the
chosen frame. Figure 4.
Bifocal Field of vision in Cosmetic Jump Prism in near
Type two areas appearance due to main 2. Vertex distance
Poor-always lens
Round Excellent distance, Excellent, induce jump Very good for The vertex distance is the distance
segment some lower field particularly particularly plus powers from the back of the spectacle lens
also, but offers small seg bad in large to the corneal plane. The effective
widest field very fused glass diameters Good for minus power of the spectacle lens is
low in segment Greatly powers as dependent on its vertex distance
reduced NVP close to especially for prescriptions above
D segment Good distance with Best in fused compared segment centre -5.00D. Minus lenses become
some lower side glass but with round Same as D weaker and plus lenses become
field - widest part poorer in - still some segment stronger when moved away from
of segment right plastics as jump the eye. For PAL dispense a shorter
below line - diameter Same as D vertex distance will require longer
increases segment corridors and vice versa. The vertex
distance can be measured using a
C segment Same as D segment Curved top simple millimeter ruler (Figure 5)
gives better or a distometer.
cosmetic
impression 3. Pantascopic angle and tilt

Executive Excellent in both Very poor No Jump at can cause The pantascopic angle is a frame
segment distance and Near all. “chain lifting” measure and is the angle formed
in plus powers by the frame front to the temple
areas due to base up while the pantascopic tilt is a face
prism measure and is the angle formed
by the lens to the horizontal eye
axis. The pantascopic tilt can
range between 0 and 15 degrees

10 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

Figure 4: Measuring fitting height (left) and monocular PD (right) important to ensure eye lash
Pic courtesy: www.opticianonline.net clearance while providing frame
wrap angle. Wrap angle ensures
any pantoscopic angle measuring better visual comfort for a PAL
gauge. The pantoscopic tilt needs to wearer by bringing the near area
be adjusted first before measuring closer to the eyes and optimising
the monocular PDs, fitting heights the lens performance.
and vertex distance. A good knowledge about
lenses, frames, facial and frame
Figure 5: Vertex distance measurement Figure 6: Pantoscopic angle and tilt measurements will go a long way
Pic courtesy: www.opticianonline.net Pic courtesy: www.2020mag.com in helping us dispense as well as
recommend the right spectacles for
and depends on the wearer’s 4. Frame wrap angle or dihedral our patients.
natural posture. In a PAL design angle References
pantoscopic tilt ensures that the 1. Griffiths A. Practical Dispensing,2000
reading portion is brought closer Theframewrapangleorthedihedral ABDO publication
to the wearer and also increases the angle describes the horizontal angle 2. BrookesC and Borish I. System for
filed of view through the reading of the lens plane in front of the eyes. Ophthalmic Dispensing, 2007, 3rd
portion. The pantoscopic tilt and The angle indicates the amount of edition
vertex distance together contribute curvature a frame has towards the 3. Obstfeld H. Spectacle frames and their
towards utility and comfort of wearer’s face. The wrap angle for dispensing, 2000
the progression corridor in a PAL PAL is usually in the range of 5 to 4. Jalie M. Ophthalmic lenses and
wearer. A decreased pantascopic tilt 7 degrees while that for sportswear dispensing, 2000
generally requires a longer corridor and wraparound sunglasses have 5. Carlton Jenean ‘Necessary Measures’
and vice versa. The pantoscopic large wrap angles to conform to Eyecare Business, Volume: 29, Issue:
angle and tilt can be measured with the contour of the face. It is also September 2015, page(s): 98, 100-102
6. Santini Barry ‘Position of Wear’
www.2020mag.com, January 2011
7. CET articles from www.opticianonline.
net

Corresponding Author:

Dr. Anitha Arvind
Freelance Consultant
Optometerist and Educator
Bangalore

www.dosonline.org/dos-times DOS Times - Volume 26, Number 3, November-December 2020 11

Subspeciality - Refraction and Spectacle Prescription

Artificial Intelligence and Eye

Ajeet Bhardwaj Optometrist,
Founder & Director, Optique, Vasant Vihar, New Delhi.
Past President, Asia Pacific Council of Optometry and Indian Optometry Federation

With the second largest elderly are investing billions of dollars into concerned with the interactions
population in the world, patients with research and development of AI. between computers and human
eye diseases are expected to increase AI is a very promising sector, many (natural) languages.
steeply. Poor eating habits and a technology companies are creating
sedentary lifestyle will lead more eye a separate branch for medical AI as NLP will have the highest application
problems related to diabetes. The an independent division. IBM has in healthcare where Doctors will not
negative effect of technology on eye created Watson and Google gas created have to learn how to operate and work
health like excessive screen time and Deep mind and other companies are with computers and programs but
reduced outdoor activities will lead following suit. computers will follow all commands of
to Myopia and its risks, dry eyes and doctors and all their communications
digital eye strain. To understand AI we need to understand with patients will be put to text.
few terminologies like what is Artificial
Ophthalmology consultations are the Intelligence - Applications of Natural Language
second largest in number in health Processing are Intelligent Search ,
care. The skewed number for eye care AI is a subfield of computer science that Machine Translation , Retail and Spam
providers will never be able to meet aims to create intelligent machines who detection .
this ever increasing demand on eye mimic and take decisions like humans
care. The need for disruption in eye care and can act or work like humans . Product applications in healthcare
and health care is rather late to arrive included a Medical diagnosis chat
in this over crowded and Lesser funded Algorithms box popularly called Virtual medical
industry funded industry. Algorithm is a step by step method Assistant which could explain prognosis
of performing a specific task given of over 600 diseases to patients and
Post offices , Banks , hotels and shopping to a computer using Mathematical saved a lot of time for doctors.
malls have seen this disruption and now calculations.
application of Artificial intelligence in A digital nurse named Sense Ly is used
healthcare will provide cost effective Machine Learning ( ML) in the NHS to help with monitoring
, accessible and consistent quality Machine learning is a subset of AI , it is an patient’s condition and follow up with
healthcare with greater speed and algorithm-based application of artificial treatments and a medical Robot in
enhanced patient satisfaction . intelligence that provides systems China passed an exit exam taken by
with the ability to automatically learn doctors prior to the practice proving
AI can support three distinct needs and improve from experience without Robots supremacy over human doctors.
being programmed.
1. Automation Deep Learning
2. Insight through data analysis Machine learning includes self driving Deep learning ( DL ) is an improvement
3. Engagement with users cars , Image diagnosis in health care , over Machine learning; it consists of
fraud detection. more layers that permit higher levels of
AI is the new focus of economical , abstraction and improved predictions
social , industrial , governance , and Natural Language Processing from data using different programs in a
healthcare development. Six companies ( NLP ) single domain .
from U.S Google, Microsoft, Apple , Natural language processing (NLP)
Amazon , Watson IBM and Deepminds is a subfield of artificial intelligence Most eye care solutions used
and 4 companies from China like Augmented Reality ( AR ) and Virtual
Biadu, Iflytek, Alibaba and Trancet Realty technologies AR technology

12 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

adds a digital layer to the real world any apps by going to youtube and Tint and understand the utility of
and creates a continuous view of both following step by step method of sunglasses .
the real and virtual worlds. A user can downloading those apps which are not
interact with the digital overlay and available in your country. If not contact 7. Polaroid UV
non-existing objects with different a software developer to help you.
types of devices. App where people can measure
AI in Optical industry amount of UV light is there in
Virtual Reality atmosphere at a particular time
VR technology creates a completely Show Window - Computer or I- Pad that day .
new reality by placing a user into strategically placed in show window
a 360-degree imaginary world. VR where your latest frames and sunglasses 8. Lens Scanner - Users can measure
completely blocks the sight of the are automatically tried on people their spectacle power any time
real world and immerses a user into standing in front of show window . anywhere just by use of smartphone.
the ultimate digital environment. A
user is totally concentrated on the all- 1. Intelligent Mirrors - Technology 9. Contact Lens Tracker - where one
embracing digital content, and his/ enhances your look by clearing all can know when the contact lenses
her brain is tricked to perceive the pimples and improve skin colour are going to expire and due for a
imaginary world as real. AMD detection before putting frames and lenses for new order.
and Rehabilitation devices user VR try on in your face .
technologies . 10. Eye Doc App - It has a database
Augmented reality like Make up of contact lenses and topical
Application of AI in windows is used by most cosmetic Ophthalmic medication where
Healthcare companies as well where make the products can be searched by
Radiology, pathology, dermatology up products are tried and shown the name of manufacturer or
and oncology were quick to adopt without applying them on your company or name . App has all
AI because most diagnosis in these face . details of parameters and range of
fields involved medical imaging. power and the availability with the
Ophthalmology has embraced medical 2. Transition virtual try on - An app manufacturer .
imaging more than other fields and by Transitions where all different
will benefit from AI. To the profession’s shades of lenses are shown to There is provision of contact lens
credit, eye care is leading the way customer without really exposing calculations for toric contact lenses
as the first specialty to receive U.S. a lens to UV or sunlight making it and conversion charts for vertex
Food and Drug Administration (FDA) easier to match with the frames and distance and also for diopter to
clearance for an autonomous screening make a choice . millimetre .
tool application called IDX -DR app
for detection grading and referral of 3 3D Virtual Try on 11. Colour blind Helper - App has 1500
diabetic retinopathy in 2018 . names of different colours which
There are many more applications Where your best selling frames are can be checked by the user .
which are available free and paid but all tried by customer through website.
apps available online are not accurate This Technology is used by NEUE 12. Colour de blind - It gives an idea to
.The accuracy of apps in healthcare Eyewear and Lenskart in ‘Optical parents and others what colour the
ranges from 7- 98% . Health care retail’ ‘by Neue Eyewear and patient with colour blindness is
providers need to make sure that the Lenkart on their websites.’ perceiving .
apps they use have validations, ratings,
accreditations and approvals from 4. Cosmetic lenses virtual try And 13. Makeup App - Anyone can use this
reputed organisations like FDA and CE Colour Studio App to dress themselves
and respective regulatory bodies of their
country and must check credentials of Shades of all available colours of The following applications are used
the developer before applying them in Cosmetic Lenses by Alcon can be primarily by ECP
their practice . tried by anyone virtually by people .
All apps listed below may not be 14. Go Check Kids - For detection of
available in your region at first try but 5. Eye colour Studio- Theatre and Amblyopia and Refractive error
if you are interested you can download Movie effects in movies can be seen by taking photograph and using
before really making these special algorithm to analyse corneal reflex
prosthetic or customised Cosmetic in preventable children
Lenses .
15. Go Check Eyes - FDA approved
6. I- Tint App measures 10 feet distance by
framing full body photographs and
We can know how much visible checking visual acuity while you
light is passing through a sunglasses are on go.

16. Peek Acuity and Peek Retina - ECP
can measure vision and take retina

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Subspeciality - Refraction and Spectacle Prescription

picture in the community using developed by MIT which is attached grading of Diabetic retinopathy.
this App . to smart phone for detection and Later google brain computers
grading of cataract . couple predict the Sex, age and
17. CRADLE - Also called White cardiovascular risks with utmost
Eye App to detect leukocoria by 23. Eye Pro App - For IOL and Toric lens accuracy using those Retinal scan
analysing white corneal reflex calculation. and applying the algorithm .
31. Air - DOC Developed in China
18. Refractive error - Refractive error 24. Cataract Boost - An app developed where algorithm applied to
detection can be done analysing by Fred hollow Foundation, Orbis, Retinal scan could detect risk of
Retinal picture and approximate IAPB, ICO and Aravind eye Hospital Brain tumour, Alzheimer’s and
ideas of Refractive error can be for measuring cataract surgery Parkinson’s besides DR
predicted . However these are the outcome and comparing results in 32. Retina AI App - Developed by A
following self Refractive devices communities and camps. Nigerian Retina specialist who
which measure the amount of used fluid intelligence to detect
Refractive error with great accuracy. 25. Lumus - inexpensive smart phone DR , ARMD , CRVO and CSR with
attachments which take Retinal greater accuracy .
a. Eye Que picture and algorithm defects
Glaucoma. Corresponding Author:
b. Eye Mitra
26. Pegasus App - developed by Ajeet Bhardwaj
c. click check by Essilor Visualty UK to analyse Retinal scan Founder & Director, Optique,
and OCT images for Glaucoma , 38 GF, Basant Lok Market, Vasant Vihar,
d. Eye Robo -2 win ( portable device DR and ARMD and gives referral New Delhi, India 110057
like a camera ) indications.

e. Eye Robo kaleidoscope ( in clinic 27. UVE - Master - Developed by Madrid
use device ) university for diagnosis of uveitis .

19. Eye calculator - App to convert 28. Kerato detect - for diagnosis and
snellen visual acuity to Log Mar and prediction of Keratoconus .
decimal Acuity .
29. IDX - DR - First ever Healthcare
20. CL Cal C app - for exact estimation app approved by FDA for detection
of contact lens axis and power grading and referral of DR using
of contact lenses it has similar Retinal Scan .
functions of Eye doc app explained
earlier . 30. DR Detection by Google -
Collaboration between Aravind eye
21. Vula App - Algorithm which detects care system and google brain where
and grade Cataract using picture of 130000 Retinal images were read
anterior segment through a smart and diagnosed by 45 US certified
phone . Ophthalmologists for detection and

22. Catra System - A small device

14 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

All you need to know about Visual
Acuity Assessment with Snellen
and LogMAR Charts

Anitha Arvind, B.S(Opt), M.Optom, PhD, FIACLE, FBDO(o/s), FASCO (VT)
Shiney Sebastian, B.S(Opt), M.Optom, FASCO(VT)
Consultant Optometrist and Educator

Introduction any correction if he doesn’t have/hasn’t Procedure
Visual acuity (VA) is a vital measure brought his spectacles. Pinhole acuity is The Chart should be well illuminated.
of visual function. The accuracy checked if the VA is less than normal. Explain the procedure to the patient.
and precision of VA measurements Near visual acuity is then checked Position the patient, at 6 m (or 20 ft)
are extremely important in the monocularly and binocularly. from the chart.
management of disease and in
occupational assessments1. The term Snellen Chart Figure 1: Snellen Chart18
20/20 vision indicates normal visual Herman Snellen, a Dutch
acuity measured at a distance of 20 feet. ophthalmologist invented the Snellen
20/20 vision does not automatically chart in 1862. The Snellen chart is
mean perfect vision. Peripheral used as a portable tool to quickly
awareness, depth perception, eye assess monocular and binocular visual
coordination, ability to focus and colour acuity3. 6/6 and 20/20 vision are the
vision also contribute to visual ability same with the difference being in only
of an individual2. Visual acuity testing the measurement of the distance at
is an important part of eye examination which the test is done. Practitioners
and needs to be done accurately in a in countries following Metric
consistent manner. measurement system usually write in
metres (6/6) whereas those following
Visual acuity testing the Imperial system write in feet (20/20).
VA is tested both monocularly and In India, we follow the Metric system.
binocularly. While testing monocularly In simple terms, 6/6 vision means that
it is preferred to test the poorer seeing one can see clearly at 6 m what should
eye first. VA is tested for distance and be seen at 6 m by a person with normal
near separately. There have been several VA. To measure visual acuity the
charts utilized by eye care professionals Snellen Chart uses a geometric scale.
since time immemorial. In clinical There are only nine letters on the chart,
practice the Snellen chart is the most known as optotypes: C, D, E, F, L, O, P,
popular, while for research studies the T, and Z3. There are many variations of
LogMAR charts are more popular. E.g., the chart available as modified by local
ETDRS (Early Treatment of Diabetic manufacturers. The Snellen chart is
Retinopathy Study) chart3. In case of a commonly preferred as it is easy to use,
child the eye charts used must be age freely available, cost effective, relatively
appropriate. Ideally VA is tested with quick and can be administered to
the patient wearing his or her current illiterates also.
spectacles/contact lenses and without

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Subspeciality - Refraction and Spectacle Prescription

Instruct the patient to cover one eye quantitative clinical scales of “counting hence are preferred to Snellen charts for
with a plain occluder or their cupped fingers” (CF), “hand motion” (HM), testing visual acuity12.
palm. They should not press on the eye. “light perception” (LP) and “no light To overcome the limitations of the chart
perception” are not suitable and need Dr Rick Ferris modified the Bailey-Lovie
Instruct the patient to read starting to be replaced by more promising tests5. chart into the ETDRS chart in 1982
from the top line of the chart from left according to the recommendations
to right. If 6/6 is not achieved, test one eye at a of the Committee on Vision of the
time using a pinhole occluder. Repeat National Academy of Sciences. This was
If the patient cannot read the letters due the whole procedure for the second eye. for use in the ETDRS (Early Treatment
to language difficulties, use a tumbling Diabetic Retinopathy) study11.
E or Landolt C chart. The patient is Limitations All the letters in the ETDRS charts
asked to point in the direction the ‘legs’ Different lines of the Snellen chart have equal legibility. These letters
of the E/ ‘gap’ in the C are facing. Keep in contain different number of letters. E.g., have a height equal to 5 stroke widths
mind that there is a one in four chance seven letters on the 6/6 line and only and have non-serif letters. There are
that the patient can correctly guess the one letter on the 6/60 line6. 14 rows of letters and each row has 5
direction. The progression between lines on the “Sloan” letters (Total - 70 letters). In
Snellen chart is not constant. 1952 Dr Sloan proposed the ‘Sloan’
The smallest line read is recorded from It is difficult to do statistical letters. There are 10 non-serif, uppercase
the markings near the end of the line. comparisons on the VA data due to the letters formed within a square outline
E.g., 6/12. variation in line progression, as well as (C, D, H, K, N, O, R, S, V, Z), with equal
the spread of the measurements7. legibility. There is consistent spacing
Incompletely read lines can be added to Crowding phenomenon due to adjacent between letters and rows, proportional
the last completely read line. e.g., 6/9+1. contour interactions reduces VA8. to letter size. This solved the problem
Some letters (i.e., L, T, A) are reportedly of crowding phenomenon as seen
Record the VA for each eye individually. easier to see than other letters (i.e., B, S, in the Snellen chart. There are equal
Remember to mention if the vision was C)9. logarithmic intervals (0.1) in the
recorded with or without correction The use of the Snellen chart is limited to progression of letter sizes between
(spectacles/contact lens). those patients familiar with the Roman3 lines. Based on the distance from the
and some Indian languages also now. patient there is a geometric progression
If the patient is unable to read the During the test, the patient must pay of the difficulty in reading the chart. VA
topmost letter on the chart at 6 metres, attention and follow the instructions scores are appreciably better on ETDRS
move him/her/or the chart closer, 1 given. This might be a challenge charts than Snellen charts especially in
metre at a time, until it can be seen for those patients who are unable to patients with poor VA11.
– the VA must be recorded with the cooperate due a physical or mental VA estimations with a LogMAR
numerator being the distance at which disability or for paediatric patients3. chart have been shown to be twice as
the patient is able to read. E.g., 3/60.
LogMAR (Logarithm of Figure 2: LogMAR Chart18
If the patient cannot read the topmost the Minimum Angle of
letter on the chart at 1 metre, then hold Resolution) chart
up your fingers at different distances At present the LogMAR (logarithm
and check at what distance the patient of the minimum angle of resolution)
can count them. This is recorded as VA chart, is the “gold standard” for testing
= CF@ --distance. visual acuity and the outcomes of
most interventions and clinical trials
If the patient is unable to count fingers, are being determined by it10. In 1976
then wave your hand and check if he/ Ian Bailey and Jan Lovie constructed a
she can see the movement. This is new chart to overcome the limitations
recorded as VA = HM. of Snellen chart11. Bailey–Lovie
LogMAR charts follow the standard
If the patient cannot see the hand recommendations for measuring VA
movements then light perception is and the optotypes used are adapted by
checked. Shine a torch close to the eye the British Standards Institutions and
and check if they can see the light. If they
can, then record VA = PL else, record VA
= NPL (no perception of light)4.

For clinical studies, quantitative
measures of VA are desirable. Semi-

16 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

repeatable as those with a Snellen chart If patient still cannot see any letters then record as CF, HM, PL, NPL, similar to that
and over three times more sensitive done while recording Snellen chart VA16.
to differences in VA between the two
eyes. This is especially important when logMAR SNELLEN DECIMAL SNELLEN (METRIC)
testing a person with amblyopia13. 1.5 20/640 0.03 6/192
1.4 20/500 0.04 6/152
Procedure 1.3 20/400 0.05 6/120
The Chart should be well illuminated. 1.2 20/320 0.063 6/96
Explain the procedure to the patient. 1.1 20/250 0.08 6/76
Position the patient, at 4 m (or 13 ft) 1.0 20/500 0.10 6/60
from the chart. 0.9 20/160 0.125 6/48
Instruct the patient to cover one eye 0.8 20/125 016 6/38
with a plain occluder or their cupped 0.7 20/100 0.20 6/30
palm. They should not press on the eye. 0.6 20/80 0.25 6/24
Instruct the patient to read starting 0.5 20.63 0.32 6/20
from the top line of the chart from left 0.4 20/50 0.40 6/15
to right. 0.3 20/40 0.50 6/12
A grading system that was introduced 0.2 20/32 0.63 6/10
with these chart design principles 0.1 20/25 0.80 6/7.5
assigns a visual acuity score according to 0.0 20/20 1.00 6/6
the number of letters read correctly. The -0.1 26/16 1.25 6/5
visual acuity is expressed as LogMAR -0.2 20/12.5 1.60 6/3.75
(the logarithmic value of the minimum -0.3 20/10 2.00 6/3
angle of resolution). On this scale, a
visual acuity of 20/20 corresponds to logMAR, logarithm of the minimum angle of resolution.
LogMAR = 0.00, 20/40 corresponds to
LogMAR = 0.30, and 20/200 corresponds Table 1: Conversion of Snellen Acuity into LogMAR, Decimal and Metric Units 8
to LogMAR = 1.00. The letter sizes on the
chart progress in 0.10-log unit steps14 Limitations
from one row to the next. There are five Not easily available.
letters on each row. Each letter on a row More expensive than conventional chart.
is assigned a value of 0.02 log units. Larger sized so less portable
The formula used in calculating the Inadequate knowledge of recording VA with LogMAR chart.
score is: More time taking than conventional Snellen chart VA assessment.
LogMAR VA = LogMAR value of the best
line read + 0.02 X (number of optotypes
missed)15.
A patient who reads all letters on the
20/50 row (log MAR = 0.40) and then
reads two more letters on the 20/40 row
(log MAR = 0.30) would be assigned
a score of 0.36 log MAR units (0.30
+0.02*3).
If patient cannot read any letters at 4 m,
advance to 2 m, and try again. If patient
still cannot read any letters, advance to
1 m, and try again16 and if still unable
then advance to 0.5 m. Add 0.3 log
units to the VA value for each time you
change the distance.

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Subspeciality - Refraction and Spectacle Prescription

Snellen Chart LogMAR Chart 10.1097/00006324-200212000-00011.
Variable no of letters in each line Same no of letters in each line PMID: 12512687.
11. http://www.academeresearchjournals
Non uniform progression of letter Uniform progression of letter sizes .org/download.php?id=49578881097
sizes 4846702.pdf & type= application/pdf
Irregular spacing between lines and Regular spacing between lines and letters &op =1
letters 12. Negiloni K, Mazumdar D, Neog A,
et al. Construction and validation of
Variable legibility of letters Similar legibility of letters LogMAR visual acuity charts in seven
Indian languages. Indian J Ophthalmol.
Less accurate grading scale Finer grading scale 2018;66(5):641-646. doi:10.4103/ijo.IJO_
1165_17
Less accurate results in low vision Greater accuracy/retest reliability in low 13. Elliott, DB. The good (LogMAR), the
patients vison patients bad (Snellen) and the ugly (BCVA,
number of letters read) of visual acuity
Table 2: Comparison of Snellen and LogMAR charts measurement. Ophthalmic Physiol
Opt 2016; 36: 355– 358. doi: 10.1111/
Conclusion 3. Azzam D, Ronquillo Y. Snellen Chart. opo.12310
The LogMAR chart provides more [Updated 2020 Jun 10]. In: StatPearls 14. I L Bailey, M A Bullimore, T W Raasch, H
accurate assessments of visual acuity [Internet]. Treasure Island (FL): StatPearls R Taylor; Clinical grading and the effects
compared to conventional charts like Publishing; 2020 Jan-. Available from: of scaling.. Invest. Ophthalmol. Vis. Sci.
the Snellen chart6. Initially it was https://www.ncbi.nlm.nih.gov/books/ 1991;32(2):422-432.
used as a research tool because of its NBK558961/ 15. Carlson, Kurts, Nancy, Daniel
better accuracy. Now a days many eye (2004). Clinical Procedures of Ocular
departments in different countries use 4. Marsden J, Stevens S, Ebri A. How Examination. U.S.A: McGraw HIll. p. 10.
it routinely in their clinical setting to measure distance visual acuity. ISBN 978-0-07-137078-3.
also especially while testing the VA of Community Eye Health. 2014;27(85):16. 16. http://ahpo.net/assets/LogMAR---low-
children, which is always a challenge. vision-recording-tables.pdf
The best charts available for testing 5. h t t p s : / / w w w . r e s e a r c h g a t e . n e t / 17. https://www.rcophth.ac.uk/wp-content/
the VA of children are those utilising publication/23232565_Resolving_ uploads/2015/11/LogMAR-vs-Snellen.
LogMAR. Now most ARMD (age related the_clinical_acuity_categories_hand_ pdf
macular degeneration) clinics record motion_and_counting_fingers_using_ 18. Quality Vision Testing Tools | Precision
vision using LogMAR as research work the_Freiburg_Visual_Acuity_Test_ Vision (precision-vision.com)
on ARMD utilised LogMAR acuities FrACT
and this research has now translated Corresponding Author:
into practice. It is not intuitive as better 6. Bailey IL, Lovie JE. New design
vision is recorded as a lower number. principles for visual acuity letter Dr. Anitha Arvind
E.g., 6/6 Snellen is 0.00 LogMAR and charts. Am J Optom Physiol Opt. 1976 Freelance Consultant Optometrist
6/60 Snellen is 1.00 LogMAR There is no Nov;53(11):740-5. [PubMed] and Educator
direct correlation between Snellen and Bangalore
LogMAR acuities. This causes a problem 7. Wadhwa RR, Azzam D. StatPearls
in analysing VA when some clinics use [Internet]. StatPearls Publishing;
Snellen and others use LogMAR17. Treasure Island (FL): Sep 7, 2020.
Variance. [PubMed]
References
8. Kaiser PK. Prospective evaluation of
1. Yukai Zhao, Luis Andres Lesmes, visual acuity assessment: a comparison
Michael Dorr, Peter Bex, Zhong-Lin Lu; of snellen versus ETDRS charts in
Accuracy and Precision of the ETDRS clinical practice (An AOS Thesis). Trans
Chart, E-ETDRS and Bayesian qVA Am Ophthalmol Soc. 2009 Dec;107:311-
Method. Invest. Ophthalmol. Vis. Sci. 24. [PMC free article] [PubMed]
2019;60(9):5908.
9. Mathew JA, Shah SA, Simon JW. Varying
2. h t t p s : / / w w w . a o a . o r g / h e a l t h y - e y e s / difficulty of Snellen letters and common
vision-and-vision-correction/visual- errors in amblyopic and fellow eyes.
acuity?sso=y Arch Ophthalmol. 2011 Feb;129(2):184-
7. [PubMed]

10. Hazel CA, Elliott DB. The dependency
of LogMAR visual acuity measurements
on chart design and scoring rule. Optom
Vis Sci. 2002 Dec;79(12):788-92. doi:

18 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

Ametropias Emanating from
Emmetropization

Roshni Sengupta1; Aaisha2; Sumit Grover3; Monica Chaudhry4
1. Faculty, 2. Faculty, 3. Associate Professor, 4. Director,
School of Health Sciences, Sushant University (Erstwhile Ansal University), Gurugram, India

Emmetropization is a developmental
process that shifts the eye from
hyperopia, that is present at
birth towards emmetropia. This
shift towards emmetropia and
maintaining its stability was
accomplished by a mechanism
first called “emmetropisierung”1 by
Straub in 1909 and later mentioned
as “emmetropisation”2. Medina later
defined emmetropization broadly
in 1987 as “the controlling process
that regulates the refraction of the
human eye to achieve optimal visual
acuity over the years3”. Based on this
definition, emmetropization is a
feedback mechanism that works by
checking the quality of the retinal
image. It also implies that if the retinal
image is altered artificially, like by the
utilization of lenses, emmetropization
is going to be misguided. In other words,
emmetropization may lead to myopia
or hyperopia instead of emmetropia

because a corrective that provides
optimal visual acuity has been placed
in front of the eye. Emmetropization
is functioning in the very early years
of life- 6 to 8 years of age as observed
by Sorsby4, since the non-Gaussian
leptokurtic distribution of refractive
errors. But myopia progression
and the effect of lenses affect older
individuals, which implies that the
emmetropization feedback, operates
after 8 years of age.

Emmetropization would also make the Fig.1. Frequency distribution showing myopic refractive errors (negative values in x-axes)
distribution of refraction for adult eyes becoming more frequent with age. The values in x-axes are vertically aligned for easy
leptokurtic and would shift hyperopic comparison. Continuous trace is the corresponding Gaussian distribution.
errors towards emmetropia if there is no [Source: Medina A. A model for emmetropization. The effect of corrective lenses. Acta
interruption. The term “optimal visual Ophthalmol (Copenh). 1987, 65(5): 565-571.]

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Subspeciality - Refraction and Spectacle Prescription

acuity” has some intentional ambiguity Fig. 2. Emmetropization feedback process as published in 1980 [7]
because it could also be observed that [Source: Medina A. El Origen de las Ametropías: ¿Qué Es Emetropía? Arch. Soc. Esp.
uncorrected optimal visual acuity is Oftalmol. 1980;40:156-161.]
accomplished not with 0D, for instance
with +1D for some individuals or group
of people and -1D for others. By the
age of 18 years, emmetropization has
made 90% of the eyes to be in a narrow
range around 0D4 (Fig. 1). Although
emmetropization is now widely
regarded as the feedback mechanism,
another school of thought supports the
passive (non-feedback) regulation.

Passive control (non-feedback) is zero, the eye is emmetropic, so the 4. followed by strongly negative
servo does not take any further action. skewness for distributions post-
for emmetropization If the difference is different from zero, teenage years.
the (-) block or error detector delivers a
Passive emmetropization proposals signal that once treated and amplified All the occurrences of these events
are generally based on the fact that the in block A is an indicator that the eye have been observed in Fig.1. Feedback
enlargement of the eye reduces the must initiate a myopic or hyperopic theory predicts a small skew towards
total dioptric power in proportion to tendency, depending on the situation. hyperopia in young individuals. This
the increasing axial length5. The power The signal is + or - respectively with theory explains myopia, which is
of the cornea and lens is reduced by the intensity that the magnitude of usually corrected, would progress
lengthening its radius of curvature, and this signal indicates. The eye begins to quickly which would not be the same
the affectivity of the lens is reduced by receive orders to change its determining in the case of hyperopia. Uncorrected or
deepening of the anterior chamber. This parameters of refraction; of which, partially corrected hyperopia8 or even
notion is considered obsolete because it the most easily commendable is the corrected hyperopia does not increase
is simply a linear scaling property of an curvature of the lens and the length significantly. The Theory predicts a
optical system6, which only explains of the anteroposterior axes. As the small positive skewness for younger
how the original (usually hyperopic) parameters vary and the ocular individuals that changes to a large
refractive error of the growing eye refraction changes in the direction negative skewness as the child grows
will be maintained without reducing. ordered by the command signal, block in the teenage years. Due to an increase
However, It does not explain the H begins to deliver to the error detector in myopic cases, this theory further
leptokurtic change of the refractive a signal that is closer to the command predicts an increased negative skewness
error distribution or the effect of lenses. signal, until, once equality is reached, with age, and also an eventual loss of
the error signal is zero and the eye stops leptokurtosis due to such increased
Active Feedback Mechanism varying its parameters7. skewness.

This theory of emmetropization is The evolution of the As an example, let us see the cause of
based on the feedback mechanism that school myopia with the light of the
connects myopia with its cause, negative frequency distribution of Servo model. An individual without a
lenses. The emmetropization servo- genetic predisposition for myopia has
mechanism is represented below (Fig.- refractive errors little chance of getting it. However, a
2). The information that the brain has sum of factors, such as small genetic
about the refractive state of the eyes is It is well known that the distribution predisposition and continued use
deduced by the states of accommodation of refractive errors in newborns has a of accommodation, especially with
of the ciliary muscle. In this figure, it normal distribution (Gaussian curve) artificial light considering that the
can be seen that the brain would be able and has a mean of a few dioptres of accommodation interval decreases
to detect ametropias in the interval of hyperopia. Feedback theory predicts with the level of illumination, causes
+5 diopters, which is been carried out the following: myopia progression of up to 3 - 5
in block «H». The block marked «-» diopters. This is because block H in
calculates the difference between this 1. Leptokurtic distribution Fig.- 2, which deduces the refraction of
signal of block H which will be between the eye based on its accommodation,
–5 (myopic) and +5 (hyperopic) and 2. the mean shift towards emmetropia takes it as hyperopic due to its frequent
the command signal. If the difference
3. the skewness would firstly be
slightly positive, and

20 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

state of accommodation and there is References 9. Shih YF et al. Effects of different
an error signal that tends to myopize. concentrations of atropine on
Prescribing glasses in these cases not 1. Straub M. Über die Atiologie der controlling myopia in myopic children.
only do not benefit from the point Brechungsanomalien des Auges und den J Ocul Pharmacol Ther. 1999;15(1):85–
of view of reducing myopia but also Ursprung der Emmetropie. Albrecht 90.
aggravates it by increasing the error von Graefes Archiv für Ophthalmologie.
signal even more7. 1909;70(1), 130-199. 10. Yen MY et al. Comparison of the effect of
atropine and cyclopentolate on myopia.
Role of low dose atropine 2. Zeeman WPC. Linsenmessungen und Ann Ophthalmol. 1989;21(5):180–187.
Emmetropisation. Graefes Arch. klin.
Numerous studies have demonstrated exp. Ophthal. 1911;78: 93-128 () 11. Shih YF et al. An intervention trial
that low-dose atropine as well as on efficacy of atropine and multi-
other cycloplegic agents are effective 3. Medina A. El Origen de las Ametropías: focal glasses in controlling myopic
in slowing myopia progression in ¿Qué Es Emetropía? Arch. Soc. Esp. progression. Acta Ophthalmol Scand.
children9,10. The basis of the atropine Oftalmol. 1980;40:156-161 2001;79(3):233–6.
effectiveness may be related to the use
of plus lenses. The Feedback theory 4. Medina A. A model for emmetropization. 12. Chia A et al. Atropine for the treatment
predicts a reduction in the rate of The effect of corrective lenses. Acta of childhood myopia: safety and efficacy
progression of myopia when using Ophthalmol (Copenh). 1987, 65(5): 565- of 0.5 %, 0.1 %, and 0.01 % doses
atropine drops due to its effect on 571. (atropine for the treatment of myopia 2).
accommodation. Atropine reduces the Ophthalmology. 2012;119(2):347–54.
accommodative amplitude of the eye, 5. Hofstetter HW. Emmetropization–
which requires that those so treated biological process or mathematical Corresponding Author:
remove their distance prescription artifact? Am J Optom Arch Am Acad
and/or use a plus lens to focus at near Optom 1969;46:447–450 Ms. Roshni Sengupta
objects11,12. Atropine users are therefore Faculty,Department of Optometry
uncorrected, under-corrected, or plus 6. Applied optics and optical design, Part Sushant University, Gurugram
corrected for near vision. In either 1 p 71 Alexander Eugen Conrady. Dover
case, the Feedback theory presumes a Publications, 1957 New York.
reduction in the rate of progression of
myopia. 7. Medina A. El Origen de las Ametropías:
¿Qué Es Emetropía? Arch. Soc. Esp.
Oftalmol. 1980;40:156-161.

8. Medina A. Prevention of myopia by
partial correction of hyperopia: a twins
study. Int Ophthalmol. 2018;38: 577–
583. https://doi.org/10.1007/s10792-017-
0493-7

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Subspeciality - Refraction and Spectacle Prescription

Consensus Statement for
Strengthening Refractive Error
and Presbyopia Services in India

Praveen Vashist1 Officer-In-Charge, Singh Senjam1 Additional Professor, Vivek Gupta1Associate Professor,
Souvik Manna1 PhD Scholar, Rohit Saxena2 Professor of Ophthalmology
1. Community Ophthalmology, Dr. Rajendra Prasad Centre for Ophthalmic Sciences, AIIMS, New Delhi
2. Dr. Rajendra Prasad Centre for Ophthalmic Sciences, AIIMS, New Delhi

Abstract and models of public private partnership roadmap to leverage Public Private
to achieve successful outcomes. Partnerships (PPP) to make India the
Refractive error and presbyopia services first clear vision country in the world
need to be scaled up as the magnitude Introduction and spur the economic growth across
of the problem is huge. The population the nation.
of ≤15 years in India is estimated at 400 Blindness and visual impairment due to
million. At a conservative estimate of refractive error is a substantial public Results
3.5% needing glasses, the annual need health problem in many parts of the
would be in the order of 14 million world.(1) In India, 10.2% of adults have URE (Uncorrected Refractive Error)
(against the current target of 1 million uncorrected refractive errors (UREs)
glasses to children by Government). and 30% of adults have uncorrected Refractive errors fit the model of a
Similarly, the presbyopic age group presbyopia, which aggregates to a disease for which screening could
(≥45 years) is estimated at 275 million total of 550 million people in need of make a significant impact on the
and most of them would benefit from spectacles.(2) This points to inadequate burden of disability in the population.
the appropriate glasses (reading or eye care services in the population It is a leading cause of avoidable visual
prescription glasses). Appropriate concerned since provision of spectacles impairment.
protocols have to be developed so that is probably the simplest and most
a child/adult with refractive error is on effective of eye care interventions Screening for refractive
a registry of some sort for triggering errors
periodic care and they are empowered to Methodology
seek the care. This consensus statement Who will Screen?
was formulated after brainstorming Keeping this in mind, a “consensus
with diverse stakeholders including meeting for strengthening refractive Gross enrolment rate (GER) in primary
leaders from government, Vision 2020 error and presbyopia services in India” and upper primary classes is high
representatives, SPOs (State Program was organized at Dr. Rajendra Prasad and hence 95% of the children can
Officers) of NPCB&VI (National Centre for Ophthalmic Sciences on 6th be covered in this group, however
Program for Control of Blindness and March 2020 from 12.30 pm to 5.00 pm the challenge arises in secondary and
Visual Impairment) from states, leading in partnership with VisionSpring. The senior secondary classes where the
eye-care NGOs (Non-Governmental event had more than 50 participants GER is comparatively less.(3) It was
Organizations), social sector and think including leaders from government, suggested to develop co-ordination
tanks. Key consensus themes were the Vision 2020 representatives, SPOs of with RBSK teams for providing primary
need for a movement on clear vision NPCB from states, leading eye-care screening and technical screening to
in India, strategies to tackle refractive NGOs, social sector and think tanks. all school-age children. Under RBSK,
error and presbyopia, suggestions for AYUSH doctor, nurse, lab technician
Government’s action plan for refractive The program witnessed insightful and AWWs do comprehensive health
error and presbyopia services in India conversations and brainstorming care screening for 30 diseases in 0-18
sessions in order to devise a strategic years age group.(4) It was suggested
that ophthalmic assistant should do

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Subspeciality - Refraction and Spectacle Prescription

eye screening along with RBSK, to training using appropriate fogging. Technological innovations such as
avoid duplication of services. It was Fogging test may be adequate to exclude Plusoptix, SV1 (Smart Vision Labs),
also suggested to use head boy or ≥+2 D hyperopia for a VA threshold of Peek Vision App, and others can be
class monitor as Vision Champions <5/10.(7) embedded as part of the screening
for peer based approach in schools to process. Autorefractor One PlusOptix
support the teachers. They can even How to Screen? has been successfully used by few
screen children around their home. states for technical screening in
An approach was suggested whereby Mobile based app for tracking which one machine is arranged per
primary screening is done by volunteers compliance and informing parents is district and it may be extended to one
followed by technical screening by much more useful than a mobile app machine per Vision Centre in future.
optometrists. Similar approach is used which measures only distance visual Using Autorefractometer in undilated
by school vision screening programme acuity of children. We need to use children may lead to undercorrection of
in Delhi Schools where primary technology to track children and send hyperopia. Noncycloplegic refraction
screening is conducted by eye care data to parents and teachers in order was shown to result in spherical
volunteers/school teachers, refractions to track compliance. However, the equivalent measurements that were
are conducted by optometrists and limiting factors are cost, maintenance consistently more negative (or less
spectacles are delivered free of cost by and calibration issues, attrition due to positive) than the corresponding
NGOs. It was also agreed by all that traveling and use etc. measurement after cycloplegia.(9) It was
primary screening for refractive errors agreed by all that subjective refraction
should only be performed when the MoHFW is already planning to develop seemed feasible, as cycloplegic
infrastructure is in place for conducting apps for vision screening because it is refraction in school setting is not
refractions and providing spectacles. always best to build a technology rather advisable. Cycloplegia can be used to
Peripheral workers/teachers should than to buy it. Long-term screening cost control accommodation, but obtaining
do the primary screening and Para- may also come down with indigenously cycloplegia is time consuming, with
medical Ophthalmic Assistants should made technology. Single optotype of blurring of vision and other possible
do refraction. It is unsound to make 6/12 corresponding to distance visual adverse effects.(10)
technical manpower like PMOA to acuity <6/12 is now accepted as the
perform screening. INGOs are very universal cut-off for refractive error Supply Chain for Spectacles
efficient in creating innovative models screening.(8) Consensus was reached on
and the lessons learnt from these models 6/12 single optotype for screening. NPCBVI’s overall India target for
can be replicated by the Government Financial Year 2019-20 was to provide
healthcare agencies. One such example Where to screen? eyeglasses to 10 lakh children, but up to
is the manual prepared by SightSavers January 2020, only 6.1 lakh eyeglasses
for school vision screening programme. Time constraints and multi-tasking were dispensed. There is a gap between
(5) The frequency of vision testing are important bottlenecks as far refraction services and dispensing of
needs to be linked to the availability of as using Mid Level Ophthalmic eyeglasses. This broken supply chain
resources. If conditions are favourable, Personnel is concerned who are must be fixed. NGOs can provide a
children should be screened once during already overwhelmed with the cataract range of pre-cut lenses with common
the primary school years (6–11years) program. Sparing two days a week for powers, but further studies are required
and once during early adolescence school vision screening by an MLOP to establish range of refractive errors
(12–14 years).(6) It was agreed that both may lead to setback in the cataract prevalent in the community in order to
primary and secondary school screening program as no other staff is available for establish what range of pre-cut lenses
in urban areas and only secondary the same. Lack of trained optometrists is required. 30-70% can be prescribed
school screening in rural areas should is also another rate limiting step in this way, and children who are easily
be done. Similarly, the more developed screening. The consensus was to screen accessible at schools can be offered
states can screen primary students, school children in the school itself. custom-made glasses after 2 weeks.
whereas the lesser affluent states can Pre-cut glasses were more appropriate
focus on the secondary age students When to screen? for mobile populations, like truckers.
for screening purposes. The consensus Colour and size options can also be
was reached that school teachers would There is an opportunity window offered to the children in order to
do the primary screening followed by of nearly 6 months (from April to make the glasses more attractive, but
technical screening by an MLOP with November excluding vacation period it needs to be ensured that there is no
minimum two years of optometry and exams) for screening annually. inadvertent interchange of glasses
between the students.
Technical Screening

How to conduct refractions?

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Subspeciality - Refraction and Spectacle Prescription

Program Management glasses to correct presbyopia in a presbyopia by non-surgical measures
randomized clinical trial from Assam. like simple reading glasses. (16,17)
Tendering process at the state (14) In Odisha, the L. V. Prasad Eye
level is much more advisable in Institute created a system for anyone Integration with existing RBSK via
comparison to district level tendering in need of presbyopia eyeglasses to ASHA/AWWs involvement was also
as standardization of quality can be avail the same through an email and pondered over. At the same time,
ensured. However, bigger states may receive their eyeglasses within 7 it was highlighted to use caution
not be able to centralize their tendering days. Scaling up of this model must while depending on ASHA workers
owing to logistic difficulties. National be explored. De-professionalization for primary screening as the quality
level tendering can be advisable only and demystification of presbyopia of screening will be highly variable.
for an agency with pan-India presence. treatment was suggested atleast for Incentives are needed at each step for
NPCB currently supports district-level presbyopic glasses. ASHA and all other staff involved in
procurement. However, this lacks the screening process without which
transparency and quality control. There has been increasing interest into they will not be motivated to work for
Hence, state level procurement should newer pharmacological treatments eye-care activities. As far as incentives
be encouraged. Similarly, technical being promoted for lens capsule are concerned, Rs 350 are earmarked in
screening and provision of spectacles softening and delaying the progression NPCB even for presbyopic spectacles
should be handled by two separate of presbyopia.(15) Most of these drops and the same can be used to give
agencies to ensure transparency and are used to soften the lens protein. incentives for the staff involved.
avoid unethical over prescription. Presbyopia correction is possible In the Indian state of Delhi, ASHA
without prescription from a technical workers are involved in refractive
Refractive error and person if someone is having only near error programme and an incentive of
vision problem, i.e. whose distance Rs. 100 from a separate pool of state
presbyopia among adults vision is normal or near normal (6/6 or funds is given to ASHAs for each pair
6/9). Majority of presbyopic clients in of spectacle delivered to any child
Presbyopia is a physiologic the country will fall into this category. with refractive error and adult with
inevitability that causes gradual loss But the issue in India is that glasses presbyopia.
of accommodation during the fifth cannot be prescribed or dispensed
decade of life.(11) Under the NPCB&VI, without assessment by qualified Apart from the targeted approach in
newer initiatives have been adopted persons. However, the mechanism select age groups, there is also the
like provision for distribution of free of dispensing presbyopic glasses to problem of unmet needs in 15-44 years
spectacles to elderly persons suffering individual who are having normal age population which constitutes the
from presbyopia to enable them distance vision can be thought of in productive age-group in the Indian
for undertaking near work.(12) The due course of time, but it is a policy population. No provision for free
government also intends to transform matter. There was a strong discussion spectacles is available to this age-group.
1.5 lakhs Sub Health Centres(SHC), about need of NGO involvement in Scarce resources need to be optimized
Primary Health Centres (PHC) and presbyopia services akin to cataract and states should look for alternate
Urban Primary Health Centres (UPHC) services in the country where NGOs sources of funding for the same.
as Health Wellness Centres by 2022 are being reimbursed for surgery.
under Ayushman Bharat Program As such, eye care is not a priority Discussion
(AB).(13) Integration of presbyopia for government, but a policy may
care within existing programs like AB- be formulated for strengthening Clear vision is a fundamental need
HWCs and NPHCE (National Program presbyopia services in the country. and is a building block for learning,
for Health care of Elderly) will be One suggested strategy is to rope in earning, road safety, and productivity.
important for long term sustainability. optical shops across the country for We should look at the same from a
If presbyopic glasses are made providing presbyopia correction, but perspective beyond just healthcare, and
available at all these centres, it will it needs consultation with various hence, it is important to involve various
lead to huge gains in terms of decreased stakeholders. ASHA workers can also other stakeholders in tackling this
burden of visual impairment due to be used for the purpose of distribution critical issue. Making reading glasses a
uncorrected presbyopia. A substantial of reading glasses in the community. commodity creates the opportunity for
productivity increase has also been Many studies in rural India have private sector to contribute towards the
documented by providing glasses to documented a complete lack of primary eye care activities, and over
correct presbyopia, with little cost awareness regarding treatment of the long run will create a sustainable
and high intervention uptake.(14) model of public private partnership.
The increase in productivity was more
than 21% due to provision of reading

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Subspeciality - Refraction and Spectacle Prescription

Multi-sectoral co-ordination in the pair of eyeglasses due to damage to Bibliography
form of consensus between ministry the first pair must be established.
of education, HRD (Human Resource Tenders must be centralized at the 1. Dandona R, Dandona L. Refractive
Development), textiles, road transport state level preferably using GeM portal error blindness. Bull World Health
and health is the only permanent (Government e-Marketplace). The Organ. 2001;79(3):237–43.
solution to the problem of refractive Government permissions for allowing
error and presbyopia in the long-term. ASHA workers to do simple presbyopia 2. Sethu Sheeladevi, Seelam B,
Ministry of HRD and education can be screening using age charts and near Nukella PB, Borah RR, Ali R, Keay
involved in pre-screening by enabling vision charts and for dispensing L. Prevalence of refractive errors,
teachers and classrooms with pre- reading glasses to those who require uncorrected refractive error, and
screening and eye health awareness them need to be looked into. Weavers presbyopia in adults in India:
skills. The education sector can be and artisans are a target group that A systematic review. Indian J
responsible for pre-screening and eye should be looked into as the incidence Ophthalmol. 2018;67(5):583–92.
health awareness creation and the of refractive error and/or presbyopia
health sector can be responsible for is very high and clear vision has 3. DISE. Elementary Education
refraction and provision of eyeglasses. direct linkages to their work. Also, an in India: Analytical Report. In:
From getting permission to screen important target group can be factory Enrolment-Based Indicators. p.
school children to (taxation-related) workers across industries, especially 101–50.
challenges for dispensing eyeglasses in across the textile and garment
the outreach, it is a constant struggle. industries. Lack of clear vision has a 4. Sharma N, Masood J, Singh SN,
Though the Government wants the direct impact on their productivity, Ahmad N, Mishra P, Singh S, et
problems to be addressed, it will help efficiency, and income and also affects al. Assessment of risk factors for
if this intention is translated into the quality of the products. There developmental delays among
enabling the service delivery and should be a Government programme to children in a rural community
proactively removing or addressing create Clear Vision Workplaces (CVW) of North India: A cross-sectional
the bottlenecks as they come up. across India.Diverse stakeholders study. J Educ Health Promot. 2019
should have a detailed discussion on Jun 27;8:112.
Recommendations making India the first “Clear Vision
Country” in the world, where everyone 5. VISION2020: The Right to Sight
The Presbyopia and School Eye- with refractive error and presbyopia India. Vision Screening in School
Screening Program must be expanded has a pair of eyeglasses to see clearly to Children: A comprehensive school
as it is not aligned with the need earn and learn better and lead safer and screening manual. 2020.
for spectacles/eyeglasses in India. better-quality lives.
A system or criteria for the second 6. Murthy G V. Vision testing for
refractive errors in schools:
Table 1: Areas of future collaboration between NGOs and GoI “screening” programmes in schools.
1 Developing an application in android or windows for refractive error Community eye Heal [Internet].
2000;13(33):3–5. Available from:
screening as well as tracking the beneficiaries for compliance and follow-up https://pubmed.ncbi.nlm.nih.
2 To generate more evidence on the benefit of providing spectacles to a target gov/17491943

group of population in improvement of productivity. 7. Esteves Leandro J, Meira J, Ferreira
3 To continue support to school vision screening program in the form of CS, Santos-Silva R, Freitas-Costa
P, Magalhães A, et al. Adequacy of
spectacles and other logistics the Fogging Test in the Detection
4 To generate more evidence on the benefit of providing spectacles to a target of Clinically Significant Hyperopia
in School-Aged Children. J
group of population in improvement of safety. Ophthalmol. 2019;2019:1–5.
5 To do a pilot study to establish range of refractive errors noted in the
8. Tong L, Saw S-M, Chan E, Yap M,
community to establish what range of pre-cut lenses is required. Lee H-Y, Kwang Y-P, et al. Screening
6 Periodical conferences with different ministries like Ministry of Education, for Myopia and Refractive Errors
Using LogMAR Visual Acuity by
HRD, Textiles, Road Transport and Health and Family Welfare to generate Optometrists and a Simplified
awareness regarding the importance of refractive errors and presbyopia and Visual Acuity Chart by Nurses.
solicit their co-operation in different inter-sectoral activities Optom Vis Sci. 2004 Oct 1;81:684–
91.

9. Zhao J, Mao J, Luo R, Li F, Pokharel
GP, Ellwein LB. Accuracy of
Noncycloplegic Autorefraction

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in School-age Children in China. 14. Reddy PA, Congdon N, MacKenzie vision: coverage, unmet needs
Optom Vis Sci. 2004;81(1):49–55. G, Gogate P, Wen Q, Jan C, et al. and barriers in a rural area of
10. Kyei S, Nketsiah AA, Asiedu K, Effect of providing near glasses on North India. BMC Ophthalmol.
Awuah A, Owusu-Ansah A. On productivity among rural Indian 2019 Dec 12;19(1):252.
set and duration of cycloplegic tea workers with presbyopia
action of 1% cyclopentolate - 1% (PROSPER): a randomised trial. Corresponding Author:
tropicamide combination. Afr Lancet Glob Heal. 2018;6(9):e1019–
Health Sci. 2017 Sep;17(3):923–32. 27. Dr. (Prof.) Praveen Vashist
11. Papadopoulos PA, Papadopoulos Officer-In-Charge, Community Ophthalmology,
AP. Current management of 15. Renna A, Alió JL, Vejarano LF. Dr. Rajendra Prasad Centre for Ophthalmic
presbyopia. Middle East Afr J Pharmacological treatments of Sciences, AIIMS, New Delhi
Ophthalmol. 2014;21(1):10–7. presbyopia: a review of modern
12. Directorate General Of Health perspectives. Eye Vis. 2017;4(1):3.
Services [Internet]. [cited 2020 May
27]. Available from: https://dghs. 16. Gajapati C V, Pradeep A V,
gov.in/content/1354_3_ National Kakhandaki A, Praveenchandra
Programme for Control of Blindness RK, Rao S. Awareness of
Visual.aspx Presbyopia among Rural Female
13. Ayushman Bharat | HWC Portal Population in North Karnataka. J
[Internet]. [cited 2020 May 27]. Clin Diagn Res. 2017/09/01. 2017
Available from: https://ab-hwc.nhp. Sep;11(9):NC01–5.
gov.in//
17. Malhotra S, Kalaivani M, Rath R,
Prasad M, Vashist P, Gupta N, et
al. Use of spectacles for distance

26 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

Understanding Contrast
Sensitivity Measurement and its
importance

Saranya S Balasubramanium
B Opt, MC Optom (London, UK), FIACLE, PG Dip Opthal (London, UK)
Principal, Acchutha Institute of Optometry

Contrast Sensitivity, being an important reciprocal of the contrast threshold. Lower the contrast threshold, higher the
form of visual function, has a role in contrast sensitivity. One must be aware of the similar reciprocal relationship
our daily life activities and needs to be between threshold and sensitivity applied in visual field testing.
assessed, in addition to Snellen’s visual Types of Contrast Sensitivity
acuity1. Checking vision with the
Snellen Chart is the most commonly Table 1. Types of Contrast Sensitivity Temporal Contrast Sensitivity
performed test to assess the visual Spatial Contrast Sensitivity Measures temporal frequency
function. However, it is possible for a Measures spatial frequency Measured using flickers
patient with 6/6 Snellen visual acuity Measured with stationary gratings Number of flickers per unit-time
to complain of visual difficulties due to Number of gratings per unit-distance
poor contrast sensitivity2. Hence, it is Commonly used in Clinical Charts
important for an eye care practitioner to
know the basics of contrast sensitivity Types of Gratings
and its clinical uses. Sine wave: Gradual change in Contrast
Square wave: Sudden change in Contrast
This article focuses on
1. Understanding ‘contrast-related’ Contrast Sensitivity Formulae 3
Letter Charts: Weber contrast = (L max – L min) / L background
terminologies Grating Charts: Michelson contrast = (L Max – L Min) / (L Max + L Min)
2. Tests for Contrast Sensitivity ((CS) where L max = Maximum illumination of the light areas of the chart
3. Clinical application of these tests
L min = Minimum illumination of the dark areas of the chart
Understanding ‘Contrast- L background = Illumination of the background
related’ Terminologies
Contrast is basically the difference in Unit of Contrast Sensitivity
luminance between 2 objects or an It is expressed in log units to have linear expression of the values and compare low
object and its background. For example, and high contrast levels.
black and white stripes have high
contrast while black and grey stripes Modulation Transfer Function (MTF)
have low contrast. Optical system’s ability to transfer spatial frequencies from the object to the image
Ratio of image contrast over object contrast
Contrast Threshold is the minimum
difference of luminance between 2
objects that can be appreciated. It is
represented by Contrast Sensitivity.

Contrast Sensitivity is thus a measure
of the contrast threshold and is the

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Subspeciality - Refraction and Spectacle Prescription

Contrast Sensitivity Function
Plot of contrast sensitivity over a range of spatial frequencies (denoted by cycles per
degree) Peak value of approx. 1-8 cycles / degree

Factors affecting the contrast The test consists of 2 charts, and two stopped when patient fails to identify
sensitivity function scoring pads. The letters of same size are 2 consecutive letters. The advantage of
Luminance, Target size, Grating motion, arranged in 16 groups of 3 letters. Each this chart is that each individual letter
Grating shape row has 2 triplets (6 letters in total), carries a score, and thus the CS may be
the second triplet fades by 0.15 log measured in 0.04 log unit differences5.
Contrast sensitivity curve unit. An external illumination of 85cd/
Curve which is used to plot the lowest mm2 is essential. The test is done at 1 m Regan Chart
contrast level detected for a particular distance, monocularly and binocularly, There are 3 charts with 3 contrast levels,
target size X axis - Spatial frequency; Y with the patient wearing his refractive 96%, 25% and 11%. The test is done at
axis - Contrast sensitivity correction. A score is given when at 3 m and patients are instructed to start
least 2 of the 3 letters in the triplet are at the top and to continue reading until
Tests for Contrast Sensitivity identified. they can correctly identify no letters on
Various Contrast sensitivity charts are a line.
available in the market. These charts A patient is marked as normal if 6-7 lines
use either letters or grating. are identified, having moderate loss of Arden plate test
CS when only 4-5 lines are identified, Consists of a booklet containing several
Table 2. Types of Contrast Sensi- and severe loss when only 1 line is sine wave gratings patterns. Each
tivity charts identified. The CS value is recorded as grating is oriented vertically with the
E.g., RE: 1.6 log CS, LE: 1.70 log CS, BE: contrast varying from the top to the
Letter Charts Grating Charts 1.80 log CS. The normal value for 20-50- bottom of the grating, lowest at the top
year olds is 1.80 log units. If monocular and highest at the bottom. The speed of
• Pelli Robson • Arden values are equal, binocular value is exposing the contrast image can affect
usually 0.05 log units more. the CS measurements.6
• Mars • Cambridge
The chart is quick and reliable, and has Cambridge low contrast grating
• Regan • Functional Acuity a wide range of contrast, and easy to It is a fast, simple screening test for
Contrast Test (FACT) perform. Although it can be memorized, contrast sensitivity, done at 6 m distance,
it is difficult to guess. The chart does with 12 pairs of plates consisting of
• Vector Vision’s have some disadvantages as with all stripes of varying contrast. The first
CSV-100 charts, the chart may fade, the external one is a demonstration plate, while the
illumination may not be even, or it rest are testing plates. The plates are
Pelli Robson contrast sensitivity could have reflections off the surface.4 sequentially changed starting from 1 till
chart the patient stops responding. Once the
Mars Chart patient stops, then the testing is started
This test is similar to the Pelli Robson at 4 plates prior to where the patient
Chart, but is smaller and used for near failed to respond. Four such series are
testing (50 cm distance). The test is completed and the score of each series is

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Subspeciality - Refraction and Spectacle Prescription

noted (numbered as per the number of plates read) and added. bottom and decreases in contrast left to right in a row. But this
The final total value is converted into contrast sensitivity chart has a poor test-retest repeatability.8
from the provided table. The testing distance is 6 m and thus a CSV1000
fairly large (20ft or 6m) testing room is required. The chances
of guessing are quite high as there are only 2 choices for the
answer i.e., which contains the gratings, and which is blank.7

Functional Acuity Contrast Testing (F.A.C.T)

This test is done a 3 m or 10ft, and the patient reports the This chart has an internal retro-illumination, thus eliminating
orientation of the grating as right, up or left and the last the uneven lighting or glare from external illumination.
correct grating seen for each spatial frequency is plotted on The test is done at 2.5 m and is used quite commonly. The
a contrast sensitivity curve. The sine-wave gratings increase types of CSV1000 chart include the CSV 1000E, CSV1000-
in frequency as one moves down the columns from top to RS for refractive surgery, CSV 1000 S and LAN-C (Landolt’s
C) for screening and CSV 1000-A for low contrast acuity
measurement.9

Table 3. Comparison of Contrast Sensitivity Charts 10

Charts Target Log CS range Step size
0.02-2.25 0.15 log unit per triplet
Pelli-Robson Chart Uniformly sized Sloan letters 0.02, 0.6, 0.96 0.0125 log per letter
0.04 – 1.92 0.04 log unit per letter
Regan Varying sized letters 0.86 - 2.0 0.088 log unit per scale division

Mars Uniformly sized Letters

Arden Sine wave gratings
(6 frequencies)

Cambridge Square wave gratings (@4cpd) 0.89 - 2.85 Variable
0.6 – 2.26 0.15 log unit per level
FACT Sine wave gratings
(5 frequencies)

CSV-1000 Sine wave gratings 0.17 – 2.3 ~0.16log unit per level
(4 frequencies)

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Subspeciality - Refraction and Spectacle Prescription

Computer Based Tests Accuracy and precision is a necessity 7. Fahy J, Glynn D, Hutchinson M.
Advantages of computer-based charts rather than a choice in terms of patient Contrast sensitivity in multiple sclerosis
include flexibility of presenting targets care. Vision assessment with a Snellen measured by Cambridge Low Contrast
in random order as well as various chart gives us the Visual acuity of Gratings: a useful clinical test? J Neurol
contrast levels, but the disadvantages the patient, but Contrast sensitivity Neurosurg Psychiatry 1989; 52:786–787
are the cost of the test equipment and measurements give us an idea of how
the maintenance of calibration. the patient perceives images in the real 8. Pesudovs K, Hazel CA, Doran RML,
world. Thus, having all the information Elliott DB. The usefulness of Vistech
Clinical importance of regarding visual function, including the and FACT contrast sensitivity charts for
Contrast Sensitivity contrast sensitivity will help deliver the cataract and refractive surgery outcomes
Contrast sensitivity is affected by highest level of patient care. research. Br J Ophthalmol 2004; 88:11–
various eye conditions. Some of the 16.
common causes of decrease in contrast References
sensitivity are ageing, dry eye, cataract, 9. Buhren J, Terzi E, Bach M, Wesemann
glaucoma, myopia and retinal diseases. 1. MJ Moseley, AR Hill (1994) Contrast W, Kohnen T. Measuring contrast
However, it is important to understand sensitivity testing in clinical practice. Br sensitivity under different lighting
that loss of CS is not pathognomonic of J Ophthalmol 78: 795-797. conditions: comparison of three tests.
a particular disease, as most conditions Optom Vis Sci 2006; 83:290–298
cause a similar decrease in CS. 2. Arden GB (1978) The importance of
measuring contrast sensitivity in cases 10. Richman J, Spaeth GL, Wirostko B.
Cataract causes a decrease due to of visual disturbance. Br J Ophthalmol Contrast sensitivity basics and a critique
decrease in light reaching the retina, 62: 198-209. of currently available tests. J Cataract
while in glaucoma, the loss of ganglion Refract Surg. 2013 Jul;39(7):1100-6. doi:
cells is the cause. Retinal diseases cause 3. Pelli DG, Bex P (2013) Measuring 10.1016/j.jcrs.2013.05.001. Epub 2013
a decrease in contrast sensitivity before contrast sensitivity. Vision Res 90: 10-14. May 23. PMID: 23706926.
the decrease in visual acuity. Refractive
surgery causes a decrease in medium 4. Pelli DG, Robson JG, Wilkins AJ. Corresponding Author:
and high frequencies post operatively. The design of a new letter chart for
Orthokeratology causes a decrease in measuring contrast sensitivity. Clinical Mrs Saranya Sachi Balasubramaniam
mesopic contrast sensitivity leading Vision Science. 1988; 2:187–199. Principal, Acchutha Institute of Optometry
to night vision difficulty. Intra-ocular Erode , TN
lenses increase the CS post operatively, 5. Dougherty, B. E, Flom, R. E, & Bullimore,
compared to the preoperative CS due to M. A. (2005). An evaluation of the
cataract. Mars Letter Contrast Sensitivity Test.
Optometry and Vision Science, 82 (11),
970–975.

6. Weatherhead RG (1980) Use of the
Arden grating test for screening. Br J
Ophthalmol 64: 591-596.

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Subspeciality - Refraction and Spectacle Prescription

Drugs used in Refraction

Roy Kumar Tapas, Halder Nabanita, Thirumurthy Velpandian
Ocular Pharmacology and Pharmacy Division,
Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi

Introduction determining the true refractive error. Drugs used in refraction
Refractive error is the failure of All the cycloplegics are mydriatic to The commonly used mydriatics
ocular system to focus images sharply dilate the pupil for better examination comprise two groups of drugs:
on the retina, resulting in blurred of retina. There are two mechanism for
vision.1 It is one of the most common dilating the pupil, one is by constricting
ocular problems that affects all the of radial muscles (by adrenergic (i) Parasympatholytic: They cause
age groups. One of the recent studies agonists) and another one is removing circular muscle dilatation and
and WHO reports indicate that the contraction of circular muscles paralysis of accommodation by
refractive error is the first cause of thereby causing relaxation (cholinergic rendering the circular muscle
visual impairment and the second antagonists). Sympathomimetic and ciliary muscles insensitive to
cause of visual loss worldwide as 43% agents like phenylephrine causes acetylcholine.
of visual impairments are attributed
to refractive errors.2,3 In a clinical dilation of iris without cycloplegia.5 (2) Sympathomimetic: which
setting, to determine the refractive imitate or potentiate the action of
errors accurately, drugs that paralyse Depending upon the duration of adrenaline and produce pupillary
the ciliary muscle and dilate the pupil action, some cycloplegic drugs can
are used. Apart from their diagnostic cause dilation of the pupil for several dilatation but no cycloplegia.
value in the assessment of refraction, These drugs potentiate the action
they are also used for the dilation of days also. Tropicamide is the best used of parasympatholytic drugs. Most
pupils to help in the ophthalmoscopic for routine pupillary dilation.6 Some
examinations and antispasmodic in studies reported that the mixed agent mydriatics reach their maximal
ocular inflammatory conditions. effect by 30 to 60 minutes,
like mixture of 1% cyclopentolate and although in children and people
1% tropicamide provides a fast onset
of cycloplegia and quick wearing off with deeply pigmented iris this
may take longer.
effect, than cyclopentolate alone.7

Refraction and Cycloplegia Constriction of radial muscles Relaxation of circular muscles
Cyclo=ciliary, plegic=paralysis or Effect of cholinergic antagonists
palsy, Cyclo+plegic=ciliary paralysis. Effect of adrenergic agonists
Figure-1: Mydriasis in eye
A cycloplegic refraction is an ocular
test where, after the instillation
of cycloplegic drugs temporarily
paralysis of the ciliary muscle takes
place that results in the loss of visual
accommodation. For determining
and correcting the refractive errors
optometrist needs to control the
accommodation of the eye so that
patients can maintain their focus on a
distant object. A cycloplegic refraction
is therefore recommended in these
cases. Cycloplegic drugs are generally
muscarinic receptor blockers.4 They
are used to dilate the pupil and
paralyze the ciliary muscle of eye for

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Subspeciality - Refraction and Spectacle Prescription

Figure-2: Sympathetic and parasympathetic innervation of the anterior segment of eye

Table-1: List of drugs used in refraction

Serial Drug Age Dose Onset Duration Side effects
no. of of action
effect 10-20 days Photosensitivity and blurring of

1. Atropine <5 years 1% 30–60 vision
ointment mins
(also as eye
drops)

2. Homatropine 5-8 years 2% drops 40-60 2-3 days Mild itching, burning sensation, photo
mins 4-6 hrs sensitivity, and blurred vision
2-24 hrs
3. Tropicamide All (used only 0.5%/1% 20-40 Transient stinging sensation, blurring of
4-6 hrs vision, photophobia, and sudden rise in
as mydriatic drops mins intraocular pressure

4. Cyclopentolate 8-20 years 0.5, 1, and 5 20-30 Burning and stinging sensation.
% drops mins Sometimes
redness of the eye, eye irritation,
conjunctival hyperemia, allergic
blepharoconjunctivitis

5. Phenylephrine All (used in 5 % / 1 0 % 30-40 Hyperemia, burning, allergy,
combination
(Used only as with drops mins photosensitivity, and hypersensitivity
mydriatics) tropicamide)

6. Scopolamine All 0.5 % drops 20-30 3-7 days Photosensitivity and blurred vision
mins

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Subspeciality - Refraction and Spectacle Prescription

Atropine in “British Pharmacopoeia” in 1890.11 Tropicamide
Homatropine is a synthetic product
In ancient time women used Atropa of tropane alkaloid atropine.12 It has Tropicamide mainly acts by blocking
belladonna (Deadly Nightshad) juice potency of one tenth of atropine. the cholinergic stimulation on
for enlargement of pupil to appear Its mechanism of action is same as circular muscle of the iris, resulting
more alluring. Italian word belladona atropine, by inhibiting the muscarinic in mydriasis. It produces cycloplegia
means “beautiful lady”.8 Atropine effect on circular muscle of the iris, by paralyzing ciliary muscles leading
is a natural alkaloid obtained from resulting in mydriasis, and causes to the loss of accommodation.21 This
Atropa belladonna. Atropine blocks relaxation of the ciliary muscle. is short and quick acting. Tropicamide
muscarinic receptors competitively Finally cycloplegia occurs by the visibly dilates the pupil after 5 minutes
and thus prevents acetylcholine to paralysis of accommodation reflex.13 and the cycloplegic effect lasts for less
bind to those sites. Muscarinic receptor It is used for various ophthalmic than one hour. For this reason it is a
(M3 receptor) present in circular conditions. It is used as mydriatics in suitable cycloplegic in busy outpatient
muscle (sphincter) of the iris, atropine post- and preoperative conditions.14 ophthalmology department.20 This is
inhibits this receptor and causes the It is indicated for the measurement a preferred agent for examination of
relaxation of the circular muscle. The of refractive errors and treatment of the lens, retina, and vitreous humour.22
cancellation of the cholinergic tone uveitis. It causes pupillary dilatation Due to its short duration of action, it is
causes domination of the adrenergic and ciliary muscle relaxation that is often used for fundus examination and
tone that finally leads to mydriasis.9 desired during acute inflammation of also used before and after eye surgery.
Atropine blocks the cholinergic effect the uveal tract. Homatropine is also Cycloplegic drops are often also used
on ciliary muscle, controlling lens used as an optical aid in some cases of for the treatment of uveitis as they
curvature and thus abolishing the axial lens opacities. reduce the risk of posterior synechiae
effect of accommodation, causing and decrease the inflammation in the
the lens to fix for far vision. Atropine Cyclopentolate anterior chamber of the eye.
causes both mydriasis and cycloplegia
in eye. Atropine causes accommodative Cyclopentolate was introduced Phenylephrine
paralysis for long time, for this reason by Treves and Testa in 1952.15 It is
it is avoided in adult patients. It is extensively used as cycloplegic for Phenylephrine is a sympathomimetic
specially used for cycloplegic refraction all ages patients with short-term amine that selectively acts on a1
in younger patients. Atropine does not cycloplegia. It is a stable water-soluble adrenergic receptors. Phenylephrine
alter IOP in the normal eye but it can ester with anticholinergic property. binds and activates a1 receptors
increase IOP in patients with narrow- It causes dilation of pupil (mydriatic) present at the radial muscles of the iris.
angle glaucoma. Generally, atropine is and loss of accommodation by Radial muscle contraction happens
used for cycloplegic retinoscopy and relaxing the ciliary muscle of the eye by the activation of a1 receptors at
dilated funduscopic examination. Use (cycloplegic).16 It has short duration the radial muscles, which results in
of atropine may prevent or slow down of action and is useful in refraction dilation of the pupil. Phenylephrine is
the progression of myopia. It has been in paediatric patients. It is also a commonly used mydriatic, instilled
speculated that in 2050, 49.8% of all prescribed for a condition of anterior before the examination of the retina.
people are expected to be myopic.10 uveitis. It is a painful condition Generally, phenylephrine is used
due to the inflammation in the eye. in combination with tropicamide.23
Considering the strong Cyclopentolate reduces pain and It is used only as a mydriatic. Use
accommodation in children, atropine relaxes the eye muscle. Clinically its of phenylephrine requires caution,
is advised to be used as an eye ointment cycloplegic effect is much better than particularly in those with angle-
form as the solutions can cause severe that of homatropine and closely parallel closure glaucoma. Concentrations
atropine toxicity owing to their to atropine.17 In younger patients greater than 0.125% cause mydriasis
higher concentration used in topical atropine is replaced by cyclopentolate, and are used for dilating the pupil.
formulations. Their nasolacrimal which has shorter duration of action
drainage can cause significant systemic and less side effects.18 After 30-45 mins Scopolamine
absorption which in turn can cause of instillation of cyclopentolate, the
atropinisation in children. eye the patient can be ready for the eye Scopolamine is a tropane alkaloid
examination.19 It is a major concern that competitively blocks muscarinic
Homatropine when cyclopentolate is used in receptors in the eye tissue. It is a more
patients having high hypermetropia, potent antimuscarinic agent than that
Homatropine was first introduced as as this may cause central nervous of atropine with shorter duration of
pupil dilator in 1881 and was taken system toxicity.20 mydriatic and cycloplegic effect.13 It
is used for temporary dilation of the

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Subspeciality - Refraction and Spectacle Prescription

pupil and paralysis of certain parts nasolacrimal duct. It’s a good refractive errors: environmental and
of the eye for diagnostic procedures. practice to place one drop in the genetic factors. Annu. Rev. Vis. Sci. 5,
Scopolamine is used for dilation of the lower fornix of the eye and ask the 47–72 (2019).
pupil for eye examination. It also used patient to close eyes for the period
before or after eye surgery for reducing of 2-3 minutes. Moreover, applying a 2. Lee, C. M. & Afshari, N. A. The global
pain and swelling in certain types of gentle pressure at the medial canthus state of cataract blindness. Curr. Opin.
eye inflammation (iridocyclitis) by to close the nasolacrimal drainage Ophthalmol. 28, 98–103 (2017).
relaxing the eye muscles. It is also will help to increase their precorneal
reported that scopolamine is used for residence time along with decrease 3. WHO. Blindness and vision
motion sickness may cause mydriasis their drainage to cause systemic impairment: Refractive errors. World
in patients.24 side effects. Incase of paediatric Heal. Organ. 6–8 (2013).
population, refraction may better be
Drugs used for the reversal achieved with the help of atropine 4. Hiatt, R. L., Braswell, R., Smith, L. &
eye ointment rather than drops to Patty, J. W. Refraction using mydriatic,
of mydriasis avoid frank atropinization. One large cycloplegic, and manifest techniques.
drop (approx. 50µl) of 1% atropine is Am. J. Ophthalmol. 76, 739–744 (1973).
Pupillary dilation during refractory expected to deliver 0.5mg of atropine
and ophthalmic investigative on the eye. For an effective comparison 5. Ostrin, L. A. & Glasser, A. The effects of
procedure cause severe patient one must keep in mind that systemic phenylephrine on pupil diameter and
discomfort after the procedure. Inorder administration of atropine as less as accommodation in rhesus monkeys.
to increase the patient compliance 0.5mg (dose in one drop) itself can Invest. Ophthalmol. Vis. Sci. 45, 215–
mydriatic reversal has been attempted cause the initiation of cardiac slowing, 221 (2004).
with agents like dapiprazole. It is an dryness of mouth and inhibition of
alpha-adrenergic antagonist reported sweating. Topical anticholinergics 6. Park, J.-H., Lee, Y.-C. & Lee, S.-Y.
to reverse the mydriasis caused by like atropine, tropicamide etc. can The comparison of mydriatic effect
anti-cholinergic (tropicamide) as well induce dryness of eye after refraction between two drugs of different
symphatomimetic (phenylephrine) or eye examination, therefore subjects mechanism. Korean J. Ophthalmol. 23,
agents in eye. Dapiprazole is used must be informed about it and if 40–42 (2009).
at the concertation of 0.5% eye required tear substitute must be
drops which is effective and safe in advised. Similarly, in cardiac patients 7. Kyei, S., Nketsiah, A. A., Asiedu, K.,
reversing mydriasis after instillation phenylephrine at the pharmacological Awuah, A. & Owusu-Ansah, A. Onset
of tropicamide 1% and phenylephrine doses for ophthalmic use can cause and duration of cycloplegic action of
2.5%. It has been reported that after the increase in blood pressure. 1% cyclopentolate – 1% tropicamide
instillation of dapiprazole the effect combination. Afr. Health Sci. 17, 923–
of mydriasis is reversed in 3 hours In conclusion, drug used for refraction 932 (2017).
time. However, dapiprazole did not should be selected based on the
show any effect on the recovery from appropriate requirement, particularly, 8. Wygnanski-Jaffe, T., Nucci, P.,
accommodation. Upon application duration of action. Drugs used for Goldchmit, M. & Mezer, E. Epileptic
it has been reported to cause mild mydriatic purposes are very potent and seizures induced by cycloplegic eye
stinging, burning and hyperemia in are sometimes in high concentrations drops. Cutan. Ocul. Toxicol. 33, 103–
the subjects. with repeated administration to 108 (2014).
achieve desired effect. Therefore
Precautions to be exercised they should be used cautiously in 9. Halder, N., Saxena, R., Phuljhele, S. &
high risk patients with comorbidities Velpandian, T. Drugs Acting Through
while using mydriatics as severe systemic side effects can Autonomic System for Ocular Use. in
happen with cycloplegics. In recent Pharmacology of Ocular Therapeutics
Nasolacrimal drainage of mydriatics days combination of cycloplegic drugs (ed. Velpandian, T.) 159–205 (Springer
can cause systemic side effects are used instead of single drug which International Publishing, 2016).
in the sensitive population. provides deep cycloplegia and quicker doi:10.1007/978-3-319-25498-2_6.
As both anticholinergic and wearing off effect.
symphathomimetic agents are 10. Holden, B. A. et al. Global prevalence of
highly water soluble and having low References myopia and high myopia and temporal
corneal penetration, they are used trends from 2000 through 2050.
in higher concentration to achieve 1. Harb, E. N. & Wildsoet, C. F. Origins of Ophthalmology 123, 1036–1042 (2016).
desire mydriasis. Therefore, one
must anticipate their systemic effect 11. THORNE, F. H. & MURPHEY, H. S.
incase of their drainage through Cycloplegics. Arch. Ophthalmol. 22,
274–287 (1939).

12. FRASER, R. A. Drugs Used in Refraction.
Australas. J. Optom. 10, 319–321 (1928).

13. Marron, J. Cycloplegia and mydriasis
by use of atropine, scopolamine
and homatropine-paredrine. Arch.
Ophthalmol. 23, 340–350 (1940).

14. Shutt, L. E. & Bowes, J. B. Atropine and

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Subspeciality - Refraction and Spectacle Prescription

hyoscine. Anaesthesia 34, 476–490 mydriatic and cycloplegic agent: a 24. Chiaramonte, J. S. Cycloplegia from
(1979). pharmacologic and clinical evaluation. transdermal scopolamine. N. Engl. J.
Am. J. Ophthalmol. 38, 831–838 (1954). Med. 306, 174 (1982).
15. Priestly, B. S. & Medine, M. 113–131.
75 GT. Am J Ophthalmol 34, 521–572 20. Ebri, A., Kuper, H. & Wedner, S. Cost- Corresponding Author:
(1951). effectiveness of cycloplegic agents:
results of a randomized controlled Roy Kumar Tapas
16. Bagheri, A., Givrad, S., Yazdani, S. trial in Nigerian children. Invest. Ocular Pharmacology and Pharmacy Division,
& Mohebbi, M. R. Optimal dosage Ophthalmol. Vis. Sci. 48, 1025–1031 Dr. Rajendra Prasad Centre for Ophthalmic
of cyclopentolate 1% for complete (2007). Sciences, All India Institute of Medical Sciences,
cycloplegia: a randomized clinical trial. New Delhi
Eur. J. Ophthalmol. 17, 294–300 (2007). 21. MILDER, B. Tropicamide as a
cycloplegic agent. Arch. Ophthalmol.
17. GETTES, B. C. & LEOPOLD, I. H. 66, 70–72 (1961).
Evaluation of five new cycloplegic
drugs. AMA Arch. Ophthalmol. 49, 24– 22. Iribarren, R. Tropicamide and myopia
27 (1953). progression. Ophthalmology 115, 1103–
1104 (2008).
18. Alkhairy, S., Rasheed, A., Mazhar-Ul-
Hassan & Siddiqui, F. Cycloplegic 23. Zhao, X. et al. An UPLC-MS/MS Method
refraction in children with for Simultaneous Determination of
cyclopentolate versus atropine. Med. Tropicamide and Phenylephrine in
Forum Mon. 26, 6–9 (2015). Rabbit Ocular Tissues and Plasma. J.
Ocul. Pharmacol. Ther. 36, 282–289
19. Gordon, D. M. & Ehrenberg, M. H. (2020).
Cyclopentolate hydrochloride: a new

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Subspeciality - Refraction and Spectacle Prescription

Objective Refraction - A Clinical
Perspective

Shenbagam N, B.S , M.Phil Optometry
Assistant Professor, Department of Optometry and Vision Science, Amity Medical School,
Amity University Haryana, Panchagaon

The ways of determining the refractive The manual and automated versions of principle, where the examiner shines
power of the eye are broadly by two this objective techniques are explained, the light (simulates) into the patient’s
methods the objective refraction and below. eye and observes the reflection (reflex)
the subjective refraction. The need for Retinoscopy of the patient’s retina. The examiner
objective refraction is basically for the The purpose of the retinoscopy simulates infinity at the working
subjective adjustment aimed at placing is objective measurement of distance (approximately 66 cms) or
the corrective lenses to obtain the Best refractive error (Spherical ametropia, arm’s length to obtain the refractive
Corrected Visual Acuity (BCVA). This Astigmatism). This technique is power of the subject’s eye.
BCVA forms the basis for best diagnostic performed manually where the
information to understand the nature examiners precise judgement plays Procedure:
of the refractive state of the eye1. major role. Therefore, to master the skill The patient is seated comfortably,
it requires adequate hands-on practice. allowed to fixate at an object preferably
Role of objective refraction When performed by experienced 6/60 Snellen’s target at a distance of
In a comphrensive eye examination clinician retinoscopy is more accurate 6 meters. The subject is instructed to
of the eye, the objective measurement than automatic refraction, hereby look at the far point, so that his /her
of the eye is the initial part of the giving a better starting point to the non- accommodation is relaxed.
assessment to find the common cycloplegic refraction4. The retinoscopy yy The examiner should simulate
refractive conditions like hyperopia, methods are further classified into Static
myopia and astigmatism. This Retinoscopy and Dynamic Retinoscopy. infinity at the working distance to
can be done by using automated Static Retinoscopy obtain the refractive power
refractometers or manually through This technique is based on the Foucault’s yy The required lens power to be placed
Retinoscope. Objective techniques also in front of the patient’s eye in order to
provide information about additional Welch Allyn Retinoscope compensate for the working distance
ocular morbidities. While performing
retinoscopy, based on the nature of reflex
from the subject’s retina, examiner can
understand the condition. In cases of
any media opacities or dense cataracts,
the reflex would be very dull irrespective
with high or low powered trial lenses
placed. An irregular scissoring reflex
is noted in Keratoconus2, a corneal
ectatic condition. White reflex is noted
in Retinoblastoma2.Variant myopia, a
refractive discrepancy found between
the objective and subjective values
may be due to thinner choroids present
compared to that of the fellow eye and
it’s not an accommodative etiology.3
The components of objective refraction
are Refractometry and Keratometry.

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Subspeciality - Refraction and Spectacle Prescription

yy Working distance lens (WD) - refractive error is present, we need to Procedure
Depends upon what distance is use spherical powers and streak each of yy The dynamic card is fitted over the
comfortable for the examiner to the primary meridians. While one of the
reach and operate on the trail frame meridians is neutralized with spherical retinoscope
(Arm’s length -66cms) power, the cylindrical lenses are used to yy The test is done in normal room
neutralize the other principal meridian.
yy Reflex: The reflected light from the The obtained refractive error is noted in illumination
patient’s retina the negative cylindrical form. (example yy Patient wears the objective distance
OD +2.00DS/-1.50 DC X180 OS: -1.00DS/-
yy The light of the retinoscope seen in 0.75DC X 180). correction
the patient’s pupil yy The examiner to be seated at same
Dynamic Retinoscopy
yy With motion - The movement of Dynamic retinoscopy as the name level of the patient
the reflex and the intercept are in the dynamic itself suggests accommodation yy Patient to read the letters on the
same direction is active unlike static retinoscopy. The
purpose of the test is to find the lag or dynamic card on the retinoscope
yy Neutralized with Plus lenses. lead of accommodation. binocularly
Hyperopes, Myopes less than 1.50DS yy Very quick retinoscopy at 40 cm. &
(WD 66 cm) &emmetropes Scope vertically in each eye
yy Estimate amount and direction of
yy Against motion -The movement of movement
the reflex and the intercept are in the yy With motion - accommodative lag,
opposite direction Against motion- lead
yy Quickly neutralize for the lead or lag
yy Neutralized with Minus lenses Lag or lead of accommodation is
yy Seen in Myopes more than 1.50 DS measured by the dioptric difference
between the accommodative stimulus
(for a WD 66 cm) and accommodative response. If the
yy Neutrality -The point at which patient’s accommodation is equal to
that required for the fixation distance,
the streak disappears and the pupil the dynamic and static retinoscopy
becomes completely filled with light results will be equal. The normal
yy Net refractive power -The power of expected values range between +0.25
the Working distance lens less the DS to +0.75DS.
dioptric equivalent of the working
distance is the measure of the Cycloplegic Refraction
refractive error
Examiners eye level should be same Cycloplegic refraction measures the
as that the subjects eye level. The refractive error in the absence of
right and left eyes of the subjects are accommodation. It is accomplished
examined by the examiners right and through the use of cycloplegic topical
left eye respectively to avoid off axis ophthalmic solution. They are generally
retinoscopy5. When the astigmatic performed in conditions to confirm the
presence of latent hyperopia, to relieve
Working Distance -Lens accommodative spasm, to eliminate
the possibility of accommodative
spasm causing pseudomyopia and in
nonverbal children.

Keratometry:
The 2/3rd of the refractive power of the
eye is from corneal surface. Any amount
of greater than 2.00DC cylindrical
power found while performing static
retinoscopy, then keratometry needs
to be performed to find out the reason
for the cylindrical component which

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Subspeciality - Refraction and Spectacle Prescription

may again be due to corneal surface is that it can be easily learned by 3. Jameel Rizwana Hussain et al. Variant
or due to internal astigmatism by the medical personnel, but the major Myopia :A new Presentation? Indian J
crystalline lens surface. The purpose disadvantage in autorefractometer is Opthalmol :2018 Jun; 66(6): 799–805
of keratometry is to measure the its, inconvenient in babies and infants1.
anterior corneal curvature and for Trained lay and nurse screeners while 4. Jorge et al. Retinoscopy/
detecting & measuring astigmatism. screening 1452 children in two different Autorefraction:Which is the best starting
The other indications of Keratometry autorefractors, it was found that the point for a non cycloplegic refraction?
are for corneal curvature in prescribing inter tester agreement were similar for Optom Vis Sci: 2005 Jan;82(1):64-8.
astigmatic correction, for corneal refractive measurements irrespective
curvature in Contact Lens Fitting, of children age7. In case of challenging 5. Glickstein M,Millodot M.Retinoscopy
Contact Lens after care for CL induced conditions like Advanced Keratoconus, and eye size.Science.11970 May
corneal surface changes, Curvature of Pterygium and any media opacities 1;168(3931):605-6.
rigid CL measurement and Assessing autorefractor will not be able to pick
stability of tear film. the refractive error, In such conditions 6. Erin M Harvey et al. Reproducibility and
skilled retinoscopist perspective along accuracy of measurements with a hand
Auto Keratometry and with subjective refraction in achieving held refractor in children. British journal
Manual Keratometry the best corrected Visual Acuity is far of Opthalmology:1997;81:941-948.
In case of distorted mires, infants and superior .
elderly subjects who are not able to 7. Jiayan Huang et al.Inter-tester agreement
comprehend the examination auto Conclusion in refractive eroor measurements.
keratometry would be the ideal choice. In a comprehensive eye examination, Optom Vis Sci
However, the central steepest and the there are several steps and procedures
flattest corneal curvatures are measured involved starting from adequate history 8. :2013 ;90(10):1128-1137.
by both these instruments. However, till dilated fundus examination. Every
the auto keratometry are quicker step needs to be in coherence for the 9. SunderRaj, P. Clinical comparison of
and easier to perform, its accuracy is better understanding of the refractive automated and manual keratometry in
compromised for the calculation of IOL and ocular pathologies. Objective pre-operative ocular biometry. Eye 6,
power8,9. refraction is one such vital procedure 60–62 (1992).
which in turn is directly related to
Auto-Refractometry and the subjects best corrected Visual 10. Minwook C,Su-Yeon Kang,Hyo Myung
Retinoscopy Acuity. Learning the skills, nuances Kim. Which Keratometer is most reliable
Autorefractometer are more commonly in its techniques and inference will while correcting Toric Intraocular
used. Retinoscopy and automated contribute much to the community and lenses? .Korean J Opthalmol.2012 Feb;
refractometry yield comparable to the primary eye care professional. 26(1):10-14.
results1. In another study, the
reproducibility of the handheld References 11. Theodre Grosvenor.Primary Care
autorefractor were similar to that of Optometry 2007 :5th edition
cycloplegic, on cycloplegic retinoscopy 1. D.Friedburg.Objective determination of
and subjective refraction6. The major Refraction. Fortschr Opthalmol:1990;87. 12. William J Benjamin . Borish’s Clinical
advantage of the auto refractometer Refraction 2006:Preface to the second
2. Jack J Kanski. Clinical Ophthalmology edition of Borish’s Clinical Refraction.
systematic Approach.6th edition 2007.

Static Vs Dynamic Retinoscopy

Static Retinoscopy Dynamic Retinoscopy Corresponding Author:
Measures the refractive power Measures the refractive power when
when accommodation is at rest accommodation is active Ms. Shenbagam N
Performed at Dim illumination Performed in normal room illumination Assistant Professor
Working distance lens required Working distance lens not required Department of Optometry and Vision Science,
Fixation target given at 6-meter Fixation target given at 40 cms Amity Medical School, Amity University
distance Haryana, Panchagaon
Emmetropia or Ametropia is Accommodative Lag or lead is determined
determined

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Subspeciality - Refraction and Spectacle Prescription

Refraction in a Visually Impaired
Person

Anitha Arvind, B.S(Opt), M.Optom, PhD, FIACLE, FBDO(o/s), FASCO (VT)
Shiney Sebastian, B.S(Opt), M.Optom, FASCO(VT)

Introduction Table 1: Classification of visual impairments according to the International Classification
World Health Organization (WHO) of Disease-10 2016 revision1
data from 2010 reports that there were
an estimated 285 million people living Examination of the visually the best corrected visual acuity
with visual impairment worldwide. Of impaired: which forms the basis of the next
these, 39 million were reported as blind The three components of a component
and 246 million as having low vision. comprehensive eye examination in the 3. Low vision intervention which
The most common causes (80%) of visually impaired are as follows: involves determining the
these visual impairments are treatable appropriate low vision aid based on
conditions such as uncorrected 1. Identifying the cause for low vision the needs of the visually impaired
refractive errors and cataract1. which includes a comprehensive A detailed and comprehensive goal-
history taking followed by based history is the primary component
Definitions of low vision and blindness assessment of vision of comprehensive eye examination for
may vary between countries. In India, the the visually impaired. It should include
NPCB (National Program for Control of 2. Careful refraction to determine details of the current problem, past
Blindness) defines low vision as “Visual the refractive status and document
acuity of less than 6/18 but equal to or
better than 6/60 in the better eye with
available correction or a visual field less
than 10° from the point of fixation”2.

Assessing the refractive status and
performing a good refraction is the
foundation of any comprehensive eye
examination and especially so for a low
vision work up. Refraction in visually
impaired is often an underestimated
component in evaluation of a visually
impaired as it is thought that the
impairment is secondary to a pathology
and there would be no scope of
improvement in vision other than low
vision aids. Refraction forms the basis
for deciding the appropriate low vision
aid for the visually impaired and in some
occasions, there could be a measurable
increase in distance or near acuity
through appropriate lenses without the
need for magnification devices. Hence
assessing the refractive status and
determining the best corrected visual
acuity in visually impaired should be an
important part of the eye examination.

www.dosonline.org/dos-times DOS Times - Volume 26, Number 3, November-December 2020 39

Subspeciality - Refraction and Spectacle Prescription

ocular history, diagnosis, test reports patients. These charts use logarithmic corresponds to a lower logMAR score1.
and general health. Details regarding progression, and the lines include equal The logMAR chart is used at 4 m and
age, address, family members, current numbers of letters of similar legibility. the distance can be reduced till 0.5 m in
profession, current academic status, Each line has a score of 0.1 logMAR and steps if the patient is unable to identify
financial status are equally important. each correctly read letter has a score of the topmost line. HOTV and LEA
It is vital that adequate time be allocated 0.02 logMAR. Better visual acuity (VA) symbols chart can be used for children4.
for the low vision assessment and
intervention.

Points to remember during
refraction of the visually
impaired
- Observe the patient behaviour

before and during examination as it
could provide valuable information

- Head turns, searching eye or head
movements can indicate that the
patient is using eccentric viewing
or has scotomas

- Good performance in the middle-
size range with difficulty in
identifying large letters, could point
to a small central island of vision

- If significant latent nystagmus is
present, a lens must be used to blur
the eye not being tested instead of a
solid occluder

- Refraction of low vision patients
should be conducted using trial
frames and or clip on lenses. Avoid
use of phoropter or refractors for
the visually impaired

- Perform retinoscopy briefly as too
much time spent on retinoscopy
could bleach the retina and this
could affect subjective refraction

- Larger dioptric changes in sphere
and cylinder powers can elicit
significant subjective responses
compared to minor dioptric
changes.

Visual Acuity Fig 1 LogMAR chart9 and LEA symbols chart10
Distance Visual Acuity –Examination
should be performed under standard
conditions with suitable charts. Most
of us are used to testing distance visual
acuity using standard Snellen charts.
The Bailey-Lowie or Early Treatment
Diabetic Retinopathy Study charts
that are logMAR-based are preferred
over Snellen charts for low vision

40 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

Fig 2: The Berkeley Rudimentary Vision Test (BRVT) and the MNREAD near vision chart9.

The Feinbloom chart and the Berkeley Refraction retinoscopy is ideal. When a clear reflex
Rudimentary Vision Test (BRVT) are Approximately in 15% of patients cannot be obtained in retinoscopy,
used for patients with advanced vision referred for low vision rehabilitation, one can go closer to the patient
loss. BRVT is done using cards that functional vision can be restored until a reflex is seen and appropriate
are held at 25 centimetres (10 inches). by simply prescribing appropriate dioptric adjustments in power is done
These portable tests eliminate the use distance and/or near vision spectacles1. according to the working distance1,6.
of the semi-quantitative clinical scales The importance of excellent refraction One needs to keep in mind that high
like “counting fingers”3. during a low vision assessment can’t be refractive errors could also be a cause
Near Visual Acuity - Charts that overstated. Exhaustion and frustration of dull retinoscopic reflexes without
include continuous text samples are can negatively impact the outcome any lenses in place in the trial frame.
better for assessing near vision than of the refraction. Ensure the person is A shorter working distance, between
charts that use optotypes. During seated comfortably and give them time 20 and 50 centimetres, will brighten a
examination, the distance between the to recover from any signs of anxiety or reflex that may be otherwise too dim
individual and the near vision chart fatigue5. to appreciate when viewed from as far
must be measured. A suitable addition When examining low vision patients as 66 centimetres. If required even off
according to the working distance of with abnormal head position, axis retinoscopy can be done to arrive
the reading chart is used. The metric eccentric gaze, or nystagmus, the use at an approximate objective value of the
M-unit is used for letter size. The near of trial frames and full aperture lenses refractive error.
visual acuity is recorded as the reading should be preferred over phoropter.
distance in meters divided by letter For children, refractive error can be Subjective Refraction
size in M-units. E.g., Near VA of 2.5 M assessed objectively using cycloplegia. After retinoscopy, the patient’s
@40 cm is documented as 0.4/2.5M. For patients with eccentric fixation, refractive error is confirmed using
The Minnesota Low Vision Reading nystagmus or media opacities dilated subjective methods such as fogging and
Chart (MNREAD) is one of the charts retinoscopy helps to provide a starting a Jackson Cross-Cylinder (JCC).
frequently used in patients with point for the refraction. While doing refraction, the test chart
low vision1. A one M-unit optotype should be at a distance where the
subtends a visual angle of 5 minutes of Retinoscopy patient can see at least the top line of
arc at 1 meter and is the size of average Although refractive error can be letters. Full aperture trial lenses should
newsprint3. A good way to assess measured using an autorefractometer be used to allow the patient to move
reading in everyday situations is to use in some patients with low vision, their head or eyes to fixate eccentrically
printed text from a newspaper or book determining refractive error by if required5.
and to ask the patient to read it aloud5.

www.dosonline.org/dos-times DOS Times - Volume 26, Number 3, November-December 2020 41

Subspeciality - Refraction and Spectacle Prescription

Since patients with poorer visual acuity and the technique repeated till the Rehabilitation of the Patient with
may have difficulty in determining best possible VA is achieved. It may be Low Vision. Turk J Ophthalmol.
small changes in lens power and necessary to refract the patient with the
clarity, it is often necessary to make chart placed at 3 m or less5. 2019;49(2):89-98. doi:10.4274/tjo.
larger power changes. The bracketing Jackson Cross Cylinder (JCC) of a higher
technique can help in such cases. The power like +/_0.75 DC or +/-1.00 DC galenos.2018.65928
examiner needs to be very patient5. is used to refine the axis when the
After retinoscopy, the patient’s VA is poorer as only with a higher 2. National Program for the Control of
refractive error is confirmed using power the patient can appreciate the Blindness. Available at: www.npcb.nic.
subjective methods with a higher Just difference. Stenopeic slit can also be in
Noticeable Difference (JND) and a JCC. The used to refine the axis. When in doubt
amount of lens power needed to elicit the Keratometry should be done to 4. https://cybersight.org/portfolio/lecture-
a noticeable change in clarity or blur crosscheck the axis7. incorporating-low-vision-into-your-
is called JND. Poorer the visual acuity, Binocular Vision Assessment, done practice/
larger the power of the JND power used whenever possible also provides crucial
in the technique. information that can be used to help 3. https://www.aao.org/preferred-practice-
JND power is determined by taking the solve the patient’s visual problems. If pattern/vision-rehabilitation-ppp-2017
denominator of the 20 ft Snellen acuity required, then suitable addition lenses
and dividing it by 100. For example, for with a power more than the usually 6. http://www.banjoben.com/low_vision_
a patient with 20/100 acuity: 100/100 = prescribed ones can be tried to see if the refraction.htm
1.00 D. Therefore, you would start your near visual acuity improves.
subjective refraction with +/- 0.50 D. 7. https://cybersight.org/portfolio/lecture-
When JND refraction techniques are Conclusion how-to-adapt-your-examination-for-a-
used, it is possible to do an accurate The importance of a good quality low-vision-patient/
refraction at any acuity level. Both refraction in a low vision assessment
sphere and cylinder corrections can cannot be overemphasized. Refraction 5. Gilbert C, van Dijk K. When someone
be done using JND technique. Most is much more challenging in a low has low vision. Community Eye Health.
importantly, JND elicits reliable vision patient when compared to an 2012;25(77):4-11.
answers from the patient7,8. ordinary one. A careful low vision
The bracketing technique is a useful refraction provides good visual acuity 8. https://www.reviewofoptometry.com/
technique in low vision refractions and measurements and ensures more article/going-old-school-a-refresher-on-
involves the strategy of presenting ‘too valuable and satisfactory solutions for retinoscopy
much plus’ and then ‘too much minus’ the patient. It is especially important
or vice versa to elicit a response which to do the assessment patiently and 9. h t t p s : / / w w w . p r e c i s i o n - v i s i o n . c o m /
could be one better than the other or using the bracketing technique with a product-category/etdrs/etdrs-charts/
no difference in either of the lenses suitable JND ensures that the refraction
presented . For example, use a +2.00 is accurate. 10. h t t p : / / w w w . l e a - t e s t . f i / i n d e x .
DS trial lens and compare this with a html?start=en/vistests/instruct/250250/
–2.00 DS trial lens. If the patient can References index.html
differentiate between the two, the lens
giving the better vision can be added 1. Sahlı E, Idil A. A Common Approach Corresponding Author:
to Low Vision: Examination and
Dr. Anitha Arvind
Freelance Consultant Optometrist and
Optometry Educator, Bangalore

42 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

Subjective Refraction

Vamshu Bhat1, B.Optom, M.Optom, Nilesh Thite2, Moptom, FIACLE , FAAO
1. Optometrist- Sharp Sight Centre, New Delhi
2. Executive Manager of Educational Programs, International Association of Educational Programs

Introduction is performed expertly or done with a component. This can be done
Subjective refraction is ‘a technique modern auto refractor. by two techniques, either by
of refining or approving objective changing the spherical power
findings by the patient’ for best dioptric Factors that can influence the (Best Vision Sphere) based on the
lens combination resulting into best response patient’s preference or by relaxing
possible and corrected visual acuity. yy In terms of Eye: accommodation of patient (fogging
During this technique, a patient is technique).
offered two or more options/ choices to - Refractive status.
differentiate between the dioptric lens - Pathological conditions. Best Vision Sphere: At starting point,
for better and clear vision. - Neurological conditions. one may begin with choices 0.50D apart
yy In terms of Patient: and introduce gradual increments of
Why is it important? - Intelligence of the patient. 0.25D for maximum results. Always
Subjective refraction enables - Emotional state. start with the plus direction first as it
development and refinement of a avoid stimulating the accommodation
prescription so that one (patient) The Four steps of subjective & keeps the method consistent. For this,
may see comfortably. Subjective refraction the endpoint is considered as the clearest
refinement is necessary to arrive at 1. Spherical correction (Relaxation of vision as reported by the patient. If the
the best endpoint of refraction for clarity between two choices is to be the
every patient, even when retinoscopy accommodation) same, always favor the lesser one.
2. Astigmatic correction
3. Monocular spherical endpoint Significance: The refinement of the
4. Binocular balance spherical part of the prescription for an
astigmatic eye places the circle of least
Starting Point confusion, or blur circle, onto the retina.
The objective findings act as a If the patient has no astigmatism, this
starting point for the subjective places the focal point onto the retina.
refraction. Alternatively, the habitual
spectacle prescription or result of Fogging: It is a widely used technique
previous subjective refraction can in the refinement of spherical
also suffice as the starting point. The component. In this technique, the
geometrical center of the trial lens initial objective is to blur the vision
needs to be aligned with the patient’s by adding a high plus (+) or minus (-)
visual axis to achieve the appropriate spherical lens to reduce visual acuity
vertex distance & pantoscopic angles. to Snellen’s 6/36. Then the power is
reduced (+) or added (-) in steps of
Monocular test: In subjective 0.25D by unfogging process until best-
refraction, certain tests are performed corrected visual acuity is achieved.
monocularly (occluding one eye at a
time). This includes: Significance: It is crucial because
varying accommodation may confuse
1. Spherical correction (Control of the retinal focus presented by each
accommodation) : An important change in the lens combinations in case
aspect to start subjective refraction of high accommodative power.
is with the refining of spherical
2. Astigmatic correction:
Determining the correct astigmatic

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Subspeciality - Refraction and Spectacle Prescription

component of refractive error is the - Repeat until both the flipped - Add or subtract cylindrical power
key effort in subjective refraction. choices appear as equally clear or according to the reported position
It can be determined via two blur. of the cross-cylinder (if same
techniques using astigmatism notation is reported as of correcting
dial with fogging technique or Significance: Locating the cylinder axis lens add the power & vice-versa)
using Jackson Cross Cylinder precedes measuring the cylinder power
(JCC) without fogging, which is because the correct cylinder power can - Compensate for change in position
a commonly practiced technique only be determined at the proper axis. of the circle of least confusion by
now-a-days. adding half as much sphere in the
JCC (Jackson Cross Cylinder): It is For Power check opposite direction.
also referred as ‘Flip Cross Technique’. - Instruct as the first step performed
This technique is used for finding Significance: For the refinement and
the axis & power of the cylindrical during Axis check.. accuracy of cylindrical power to avoid
component of the refractive error. - Align JCC axis with the principal over or under correction. JCC enables in
the shift of residual cylindrical power
It is a sphero-cylindrical lens in which meridians of correcting cylinder or which may result in change of the circle
the power of the cylinder is twice the handle perpendicular to the axis of of least confusion, thereby, affecting the
power of the sphere & of the opposite cylindrical lens in the trial frame. target by making it more or less clear.
sign. E.g. +0.50DSph is combined with - Follow the step 2 of axis check (flip
–1.0DCyl. This results in a net power & ask) 3. Monocular spherical endpoint
meridional refractive power of +0.50DC Duochrome test
in one meridian & –0.50Dc in the other This test is used to find the monocular
meridian. The principal meridians are endpoint of refraction. Each eye is
marked at the periphery of the lens to be tested separately to find out if the eye is
visible by the examiner. The handle is overcorrected or under corrected. Also,
attached midway between two marked ‘chromatic aberration’ forms the basis
meridians (red-white or red-black). It of this test. The longer wavelength (red)
comes in a variation of 0.25D, 0.50D, & is refracted less than the shorter (green).
0.75D.
With one eye occluded patient is asked
For Axis check to report visible prominent letters of
- Instruct the patient to fixate on the chart that appear clearer, darker
& sharper than other. If the letters on
one letter of the line above the best the red side appear clearer, add minus
corrected visual acuity. power; if the letters on the green side
- Position the cross-cylinder axis 450 appear clearer, add plus power to the
from the principal meridian of the lens. Neutrality is reached when the
correcting cylinder, handle parallel letters on both backgrounds appear
to the axis of cylindrical lens in the equally distinct.
trial frame.
- Flip & ask the patient to report the Points to be noted during
clearer one from both the flips as Duochrome test: If a change in lens
first or second. power produces an immediate reversal
- Rotate the axis towards the of choice from red to green, spherical
corresponding axis of the cross- power that gives a better perception of
cylinder [plus cylinder axis rotated green is the appropriate endpoint. This
to + cylinder notation of JCC (white scenario especially occurs in young
or black), minus cylinder axis patients with active accommodation.
rotated to - cylinder notation of JCC - Older patients report red because of
(red)].
- For rotating the axis, begin with the changes in the crystalline lens.
larger steps, typically 100 then as the - Instruct the patient to evaluate the
correct axis is approached, make 50
shifts. prominence of letters (clarity &
darkness), not background color.
Why is it needed: To rule out over or
under correction of the final refraction
of the spherical component.

44 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

4. Binocular balancing (Binocular practitioner should reach there as on the response from patient, but
Test) efficiently as possible. one still has to follow the rules of
4. Make sure the patient is not prescribing.
This refers to the end point of subjective squinting, as this will give an 12. Before prescribing, let patient
refraction. It is performed binocularly unwanted pinhole effect. experience (first-time users) or
when visual acuity is relatively equal 5. Run through the Sequence again if compare (habitual wearers), the
between the eyes. Binocular balancing there is a large change in any of the final power.
is not only balancing the visual acuity steps References:
but also accommodation. 6. While flipping, perform it slowly so 1. Richard J. Kolker, MD (2014), Subjective
that patient can compare easily. Refraction and Prescribing Glasses:
Alternate occlusion technique is a 7. While refining spherical power Guide to Practical Techniques and
widely used technique. show one or two lines above the Principles pdf, accessed on 2 Dec. 2020. ;
best correct visual acuity, so that 2. Mark E Wilkinson, OD (2016), Plus
- Place the final distance correction patient can differentiate better. Cylinder Subjective Refraction
in the trial frame with the patient 8. It is important to understand that Techniques for Technicians pdf accessed
viewing 6/18 line target with both some patients can give a very on 10 Dec.2020. ;
eyes. Now fog both the eyes by precise & repeatable end-point, 3. Mark E. Wilkinson, OD (2016), Sharpen
adding +0.75 D sphere. while Cataracts, macular edema, your Subjective Refraction Technique
dry eyes, age-related macular pdf accessed on 9 Dec 2020. ;
- Inform the patient to keep both eyes degeneration, & other conditions 4. William Benjamin (2006), Borish’s
open. Now, occlusion technique is can cause vision to fluctuate. Clinical refraction 2nd edition;
performed and the patient is asked 9. If the patient has reduced vision 5. Duke Elders practices of clinical
to identify the eye having clear due to eye disease or visual acuity refraction Page: 181 to 183.
vision. is worsening with the steps the
response of the patient is unreliable. Pictures Courtesy:
- Add +0.25 D sphere to the better- Here, one may go to larger jumps in Brother Opticians Pvt. Ltd, Noida
seeing eye & repeat the above steps.
step. Continue until both eyes are 10. When refracting a child, at the Corresponding Author:
equally blurred. Slowly defog until completion of the refraction,
the patient can read the 6/6 line. allow the patient to view the chart Vamshu Bhat, Optometrist ,
binocularly. Add + 0.25 diopter of Sharp Sight Centre, Metro Pillar Number 82,
Tips for Accurate Subjective sphere to each eye & determine A-15, Swasthya Vihar, Vikas Marg,
Refraction Results & whether the child’s ability to read Opp. Preet Vihar, New Delhi, Delhi 110092
Prescribing the chart is unchanged. If it is
1. Move through the four steps unchanged, continue to remove
minus binocularly until the visual
expeditiously. This makes the acuity is affected. This additional
process more efficient, precise, step will decrease the likelihood
& easier for the patient & the that a child will be over-minused as
examiner. While giving choices a consequence of their very strong
always instruct to refer as lens/ accommodative ability.
choice 1 or 2 to avoid confusion. 11. During the process of subjective
2. A good rule of thumb is have a “no refraction, the practitioner relies
pauses” policy, as it is a result of
the patient being uncertain about
which of the two lenses are better.
3. The goal is to find the smallest
line the patient can read and

www.dosonline.org/dos-times DOS Times - Volume 26, Number 3, November-December 2020 45

Subspeciality - Refraction and Spectacle Prescription

Telehealth, Refraction and
Co - Management

Rahul Bhardwaj, B.Optom
CEO Optique and Founder Neue Eyewear

Telehealth is often considered the is cost effective including in terms of In order to successfully implement
future of the healthcare industry. In the saving travel costs for both patients telehealth in eyecare, the following are
context of the pandemic, its importance and health care providers; it increases needed: a robust software to deliver the
has been further amplified and has convenience and productivity as it specialised service to patients such as
provided the industry an opportunity to allows interaction with practitioners’ Opto-Live; Video calling applications
accelerate innovation in this space. In beyond strict office hours; it bridges like Zoom, G meet etc. through which
eyecare specifically, the latest Opto-Live the gap between cities and rural areas to deploy the software; specialised
software represents this important shift as well as the gap of low availability equipment that is portable, easy to use
and the opportunity to apply telehealth of health care providers and services and accurate; a good stable high-speed
principles to the field in order to in these rural areas; it allows patients internet; and Laptop Desktop or Ipad
reach greater scale in an inclusive and to be monitored remotely thereby set-up for practitioner and patient.
innovative manner. minimising or eliminating the need
for hospital stay; emergency rooms can Once a patient is on boarded, it is
Telehealth in eyecare is important for be kept free for serious patients while critical to follow a few key steps in order
various reasons. First and foremost, others can be screened using telehealth; to provide a safe and comprehensive
for those with access to digital devices, in the case of emergencies, it also allows experience:
it provides a direct platform to critical care quickly; and finally, it • Prior to the session, consent must be
connect patients to practitioners in a enables elderly patients with chronic
convenient, inclusive and safe manner health issues to be attended to remotely, taken using a standardised format
as well as enables the delivery of high safely and as per their convenience. over email or through exchange
quality services to those without platforms like WhatsApp.
physical access or access to qualified At present, most OPDs for telehealth • Schedule an appointment and
eyecare practitioners (ECPs). Second, in ophthalmology cover only red-eye, provide a link for the tele-consult as
for those without access to digital dry-eye, strain caused by devices, and per a convenient date and time for
devices or qualified ECPs, this approach lid lumps and bumps. Opto-Live was both the practitioner and patient.
to eyecare can be used to create a created with the aspiration of expanding • During the session, record history
network of remote vision centers with these services to also address the and the chief complaint of the
minimal human resources to facilitate issues of refractive error and invasive patient appropriately.
sessions with experts in other parts issues like glaucoma, retinopathy and • If required, ensure the appropriate
of the country. Therefore, applying cataracts. In addition, based on the devices are made available to the
telehealth to this field brings about the patient’s unique needs and cases, Opto- patient either at their home or at
much needed ability to scale and reach Live also provides access to specialised the vision center
the unreached in a country strained by ophthalmologists for real time remote • For at home testing, request
access to quality eyecare. diagnosis and often, even treatment. In patients to have a spoon, spatula,
some special cases, specialised devices scale/inchtape ready for the session.
With the onset of the pandemic, this are required to fully attend to a patient’s Through telehealth consultations
scale and access has become even more need. For that, the Opto-Live team has through softwares like Opto-Live, the
important because: telehealth provides also indigenously developed low-cost, following tests can be performed:
a safe and convenient alternative to accurate devices that can be easily
visiting hospitals and centers which transported to the required patients or 1. Diagnose and correct refractive
hold a risk of spreading infection; it locations. error using digital logmar charts

46 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

8. Cover tests; Cover uncover and
Alternating cover tests can be done
using Video calling and results
can be recorded and compared
using Opto-Live and any phorias or
tropias can be detected.

9. Retina Evaluation; Various
Amsler grids and Red Desaturation
test can be done to diagnose
abnormalities in the retina. These
results can be recorded in Opto-Live
and compared with future tests.

(Distance and Near), contrast 4. Diagnose with Flowcharts for 10. Retina Imaging; An asynchronous
charts, duochrome and astigmatic Red Eye and Neuro-Ophthalmology test where a technician is sent to
fan charts. This can be done in available within the Opto-Live the Patient/ Vision centre using a
conjunction with devices such as software. portable retina scanner and images
Refractive paddles for spherical and are taken and shared with ECP.
cylindrical correction; Focometer 5. Assess Dry Eye by converting any
and self refractive devices such smartphone to a UV torch to view 11. Glaucoma evaluation involves
as the EyeQue and new Essilor eyes stained by Fluorescein to see Visual Field testing using MRF
Quickchek through which we can any staining. This coupled with the software. Retina Imaging as
assess the Objective and Subjective Iclip works very effectively. described above and measurement
refraction to give an accurate of IOP using portable tonometer
spectacle prescription. 6. Binocular Vision Function using (asynchronous) can effectively
2. Assess Colour Vision using digital ‘Bynocs’ software available within diagnose / manage glaucoma.
Charts Opto-Live through which the Icare tonometers are available for
3. Assess the Cornea, Pupil reflex, practitioner can run a series of tests purchase by patients to actively
Conjunctiva, Red Eye, Lids, Dry to test binocular vision function measure their IOP. Even though
Eye and Cataracts using a low and detect any tropias or phorias. they are expensive, the hope is
cost Iclip device developed by the Following this, virtual therapy can that these devices are available
Opto-Live team. This attachment be provided for patients to do at
increases the magnification home and assessed.
of a smartphone camera and
allows practitioners to have high 7. Convergence using pencil push up
magnification images of the test to see if eye muscles are weak
Cornea, Conjunctiva and Lens. and exercises can be demonstrated
and prescribed.

www.dosonline.org/dos-times DOS Times - Volume 26, Number 3, November-December 2020 47

Subspeciality - Refraction and Spectacle Prescription

for a low cost in the future which allows patients to try on add on service to an existing private
and become as commonplace glasses without physically holding practice for current and new patients
as a sphygmomanometer or them. This makes no inventory virtually; opening a new location
glucometer. clinics, showroom and vision making your expertise available
12. Patient History and Chief centres a reality! virtually; and finally, creating a Virtual
Complaint; a detailed history can 16. Contact Lens fitting and Evaluation; Vision Centre for community outreach
be recorded in Opto-Live and can be Use Opto-Live to measure HVID/ where your expertise reaches the
revisited and updated at any time. VVID , K readings (asynchronous) unreached and those who need it the
13. Connect with Specialised using a portable Keratometer and most.
Ophthalmologists in real time assess the fit of Contact Lenses References
and give a real time diagnosis and using the Iclip. 1. Eye Que image - https://www.eyeque.
treatment.
14. Optical Dispensing; Using Opto- com/
Live take measurement such as PD, 2. I care tonometer - https://www.icare-
ED and Diameter for an accurate
and effective spectacle fitting - both world.com/
for single vision and progressive
glasses. Corresponding Author:

15. Frame Selection; Select frames 17. Low Vision; Counsel and consult Mr Rahul Bhardwaj
using the latest AR technology low vision patients to increase their Chief Executive Officer (CEO)
productivity using the latest Apps Optique 38, GF, Basant Lok Market,
and AI. Also consult for various low Vasant Vihar
vision devices.

In the end, telehealth in eyecare is
what you make of it and presents an
important and accessible opportunity
across various scenarios including: an

48 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times

Subspeciality - Refraction and Spectacle Prescription

Progressive Lens ……. A Boon for
Presbyopes

Ananthalakshmi. N, B.Opt , M.Opt, PG.Dip in HR, Shajan Adolph, B.Opt , M.Opt
Head-Education & Professional Services -Essilor India Pvt. Ltd

Progressive lenses has gained world- two powers — one (in the top half The advantages in the progression from
wide acceptance as the most suitable of the lens) for distance vision, and a the distance portion to the reading
correction for presbyopia. As they second (in the lower half of the lens- portion, the wearer obtains all the
provide clear, comfortable, natural Segment) for near vision. These lenses intermediate powers allowing clear
vision at all distances, they have have a negative impact on Cosmesis. vision at a range of distances.
gradually replaced bifocal lenses (a The sudden shift from distance to Near
technology which is more than 200 area gives rise to “jump effect” and PAL Design Types:
years old) and are becoming used more also the wearer is not comfortable for Hard Design
and more instead of single vision lenses intermediate visual tasks. • Wide distance and near zones
for near For these reasons, Progressive lens has • Narrow intermediate corridor
become most popular choice among the • Rapid increase in unwanted
With the expected growth in the presbyopes.
population, particularly amongst the astigmatism (periphery)
elderly, presbyopes will become even How Do PALs Work? • Shorter progression (intermediate
more numerous in the years to come, Clearly to achieve a continually
hence Progressive lenses play a pivotal increasing power in the vertical zone)
role in lens Dispensing. meridian, the radius of curvature must
decrease (i.e. become steeper). The
What is Progressive Addition increasing power in the vertical meridian
Lens? (commonly referred as produces variable focal length which
PAL) will correspond with the variable
A progressive lens is a lens whose working distances of the wearer.
power increases continuously from
top to bottom, between an upper zone
designed for distance vision and a
lower zone designed for near vision.
The increase in power is obtained by a
continuous change in curvature of one
or both surfaces of the lens

In a progressive lens the lens power
increases smoothly from the distance
zone at the top of the lens through an
intermediate zone in the middle, to the
near zone at the bottom of the lens. And
the wearer benefits from continuous
clear vision from distance to near
without any visible lines.

On the contrary, a bifocal lens has just

www.dosonline.org/dos-times DOS Times - Volume 26, Number 3, November-December 2020 49

Subspeciality - Refraction and Spectacle Prescription

Soft Design
• Narrower distance and near zones
• Wider intermediate corridor
• Gradual increase in unwanted

astigmatism
• Longer progression (intermediate

zone)

Modern Soft Design The Permanent markings are: Dispensing a PAL
• Wide distance and near zones • Micro - Engraved Circles: These are These golden steps play a vital role in
• Wider intermediate corridor the success of PAL dispensing
• Gradual increase in unwanted two small micro-etching which
are positioned about 34 mm apart 1) Accurate Refraction / Prescription
astigmatism (17mm to the nasal and temporal is a requisite
• Shorter progression than traditional sides of the prism reference point).
• Lens logo and lens material. -found 2) Frame Selection – Shape, depth
‘soft’ design on the nasal side of the lens, and size has to be chosen so frame
• ‘softer’ periphery depicting the lens brand and the covers all the required viewing
Modern PAL designs provide type / index of the lens material. areas. Care should be taken not to
appropriate access to all the zones with • The add power is normally engraved choose bigger frames as big frames
adequate field of view, clubbed with on the temporal side of the lens. translate to bigger and thicker
comfort and convenience. This enables the observer to check lenses. Choose frame to fit the face
the power of the addition – neither too small or too big.
The best way to judge performance of
PALs is through clinical experience, Ink Stamped Markings 3) Frame Adjustments – this is the
level of Wearer comfort and satisfaction These Temporary ink markings are on most crucial step and often widely
the front surface of the lens. These have skipped too. Frame adjustments
How to identify a PAL? an important role in checking whether need to be done first before
There are two types of marking on a PAL the lenses are fitted (dispensed) proceeding to take the required
1) Permanent Markings correctly. measurements. The wearer has
2) Temporary Markings yy Distance reference circle. This circle to be comfortable with the frame.
Along with the normal frame
Permanent Markings is used for checking the distance adjustments, three specific frame
The Permanent markings can be found power. adjustments also need to be carried
by close observation of the lens, holding yy Fitting cross. The fitting cross is the out.
the lens up and filling the lens with point which should be fitted directly
light. in front of the centre of the patient’s Back vertex distance: Progressive
pupil. lenses should be fitted with the
yy Prism reference point. This is the smallest back vertex distance that is
point on the lens in which ordered possible. Reducing the back vertex
prism or the amount of differential distance increases the field of view
prism should be checked. through the various zones of the
yy Near reference circle. This circle is lens. Its effects are particularly
used for checking the total power for noticeable in the intermediate
Near corridor and near zone.

Pantoscopic tilt : By increasing the
pantoscopic tilt and bringing the
near and intermediate zones closer

50 DOS Times - Volume 26, Number 3, November-December 2020 www.dosonline.org/dos-times