DOS Times Vol 25 NO. 3

Subspeciality-Glaucoma

4. Bengtsson, B. and A.Heijl. A visual field 6. Keltner JL, Johnson CA, Quigg JM, Corresponding Author:
index for calculation of glaucoma rate Cello KE, Kass MA, Gordon MO, for
of progression. Am J Ophthalmol 2008 the Ocular Hypertension Treatment Dr. Dewang Angmo MD, DNB, FRCS,
145(2): 343-53. Study Group: Confirmation of visual FICO, MNAMS
field abnormalities in the Ocular Dr. R.P.Centre for Ophthalmic Sciences,
5. Prata TS, De Moraes CG, Teng CC, Hypertension Treatment Study . Arch All India Institute of Medical Sciences,
Tello C, Ritch R, Liebmann J, M Factors Ophthalmol 2000 118: 1187-1194. New Delhi, India
affecting rates of visual field progression
in glaucoma patients with optic disc
hemorrhage. Ophthalmology 2010
117(1):24-9.

50 DOS Times - Volume 25, Number 3, November-December 2019 www.dosonline.org/dos-times

Subspeciality-Retina

Post-partum Bilateral Optic
Neuropathy and Choroidal
Involvement without Eclampsia: A
Diagnostic Dilemma

Syed Faraaz Shahzad Hussain MS, Saroj I. Sahdev MS
Department of Ophthalmology, T.N.M.C & B.Y.L. Nair Charitable Hospital, Mumbai Central, Mumbai, Maharashtra, India

Summary Statement: Acute visual loss in the peurperium period, subsequently diagnosed and treated as idiopathic posterior uveitis,
with the possibility of “probable VKH” with atypical presentation.
Structured Abstract: Purpose: Highlight a case of acute visual loss after pregnancy with optic nerve and choroidal involvement, with no
eclampsia in the immediate post-partum period.
Methods: Interventional case report.
Results: A 23 year old lady presented with bilateral, sudden, painless loss of vision ten days after delivering a full-term baby and breastfeeding
the child, with routine neonatal care. Patient was normotensive and had no prior history of eclampsia. Patient was noted to have bilateral
optic disc edema along with macular edema and diffuse choroiditis. After physician, neurology, obstetric and pediatric consultation, the
patient was started on IV methyl prednisolone 1g/day, but developed febrile spike on the second day. As patient was also lactating, after due
co-ordination with specialists, a decision was taken to stop IVMP and start oral prednisolone 1mg/kg with 5 day tapering. Patient improved
on the same, and is being followed regularly.
Conclusion: Post pregnancy women with acute visual loss can have a myriad of retinal and choroidal diseases which could be vision
threatening, and rarely life threatening. Diligent and long term follow-up is necessary along with involvement of a team of specialists.
Keywords: Acute visual loss; Optic neuropathy; Pregnancy; Choroiditis; VKH.

Women are prone to visual disturbances these changes are due to heart rate, period, with no associated eclampsia.
fromavarietyofcausesduringpregnancy cardiac output, angiopoeitic factors,
and in the puerperium period1. This hormonal influences which can Case report
can include changes in refraction, combine to worsen or lead to a variety A 23 year old, primgravida presented
corneal curvature, nonorganic of retinal and choroidal issues. Optic with acute visual loss in both eyes after
factitious visual dysfunction, amniotic neuropathy along with choroiditis delivering a full term, healthy baby
fluid embolization, disseminated and macular oedema can have myriad ten days ago. The patient was lactating
intravascular coagulopathy, causes, many of whose manifestations routinely, with no eventful historical
enlargement of pituitary adenoma, can be altered due to the above changes record during pregnancy – neither
stimulation of meningioma growth, in pregnancy. Further, pregnant infective nor related to hypertensive
cortical ischemic events, multiple and lactating women often refuse to issues. The patient had no prior history
sclerosis (MS), retinopathy of undergo invasive diagnostic tests for of visual disturbance and needed no
eclampsia and anemia, other retinal safety concerns; which worsens the spectacle correction. The patient also
and choroidal diseases such as central diagnostic dilemma3. denies any known systemic diseases
serous chorioretinopathy, and We present a case to highlight the like hypertension, diabetes mellitus,
rhegmatogenous retinal detachment. importance of non-invasive tests along thyroid and tuberculosis or its contact.
Certain pre-existing conditions might with involvement of a team of specialists Her best corrected visual acuity (BCVA)
exacerbate and cause worsening of and the necessity of long term follow up was finger counting 2m (FC), not able to
vision, including diabetes mellitus, of young women presenting with acute read near or amsler charts. Pupils were
Vogt-Koyanagi-Harada (VKH) disease, visual disturbance in the puerperium central, circular, sluggishly reacting
and white dot syndromes2. Many of to light and with normal near reflex.

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Subspeciality-Retina

Figure 1: SD-OCT examination showed multiple pockets of fluid below the neurosensory decision was taken to stop IVMP and
retina, separated by septae. start oral prednisolone 1mg/kg with 5
day tapering.
Anterior segment examination was was also normal.
unremarkable, anterior vitreous was A team of specialists, involving Patient improved both symptomatically
clear. On fundus examination, both physician, neurophysician, obstetric and on examination to BCVA 6/6
eyes, media was clear, optic disc showed and pediatric was consulted. Blood for distance and N6 for near in both
diffuse hyperemia with disc edema pressure monitoring was done, eyes over a period of one month,
and obliteration of cup. Macular area hemoglobin along with complete with fundus showing resolution of
showed edema extending about three blood count, MRI brain + orbit with optic disc edema as well as retinal
disc diameters, with diffuse borders, left contrast was normal. Fever profile and choroidal inflammation. SD-OCT
greater than right. Retinal edema along along with peripheral smear was showed resolution of the fluid with
with choroidal involvement in the form performed and workup for syphilis normal contour and minimal thinning
multiple areas of inflammatory pockets and tuberculosiswas done and all were at central fovea. Color vision, amsler
with diffuse borders was noted. SD-OCT reported normal. The patient declined examination and pupils were all WNL.
examination showed multiple pockets to undergo fluroscien angiography and Automated VFA showed generalized
of fluid below the neurosensory retina, lumbar puncture examination. After constriction of both visual fields, which
separated by septae splitting the outer due clearance, patient was started on improved to normal in two months.
plexiform and nuclear layers. Visual IV methyl prednisolone 1g/day, but The patient is routinely being followed
field analysis (VFA) was apparently developed febrile spike on the second up, especially for possible underlying
normal on confrontation, but day. As patient was also lactating, after demyelination and VKH syndrome
automated could not be performed due due co-ordination with specialists, a indicators.
to poor vision. Her general examination
Discussion
Pregnancy and the postpartum
interval are times of physiologic and
psychological stress; the possibility
of nonorganic visual problems along
with corneal and fundus alterations
should be ruled out as these can lead to
generalized depression of visual fields
noted in both eyes.

Our patient had no other causes apart
from the immediate puerperium period
and lactation, but others have reported
that despite earlier reported entities of
“lactation optic neuritis”, it has not been
found to be either causative or linked to
the same. Rather it has been noted that
most such patients have underlying
MS or other demyelinating illnesses
in the long run, even after a decade4.
Our patient though had presented
with bilateral optic neuropathy, she
also showed retinal and choroidal
inflammation, well beyond the
posterior pole.

The other major disorders to rule out
are undetected hypertension, with
HELLP syndrome along with pituitary
tumours. We diligently monitored
fluctuations in BP as well as renal and
liver functions, with no significant
positive findings5. Central serous

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Subspeciality-Retina

Figure 2: SD-OCT showed resolution of the fluid with normal contour and minimal thinning such diagnosis together. Our patient
at central fovea. can likely be considered as idiopathic
non-infectious posterior uveitis with
chorioretinopathy (CSC) is unlikely Exclusively ocular findings similar to a working diagnosis of “probable
with bilateral presentation and onset VKH have been grouped as “probable VKH” as only ocular signs were noted,
after delivery, but should be ruled out. VKH” in the newer classification however the disc oedema was atypical
SD-OCT shows the demarcation well (proposed at the First International in such a young age. OCT (including
beyond the posterior pole. Workshop on VKH), which is likely enhanced depth imaging - EDI) serves as
Uveitis associated with pregnancy has in our patient. However, in contrast a non-invasive modality to objectively
been reported and studied, especially to their case series where most flare monitor progress in such patients who
non-infectious etiologies. A case series ups occurred in the early months of refuse FFA/ICG due to pregnancy and
by Rabia and Vitale6 found VKH to pregnancy, our patient only developed lactation.
be the most common cause of non- symptoms and signs in the immediate
infectious uveitis during pregnancy, post-partum period, which has been In pregnancy and puerperium a number
followed by Bechet’s disease and reported to be more often for idiopathic of causes can lead to acute visual loss
idiopathic variant, which does not fit variety. Park and Park reported a case such as eclampsia, MS, CSCR, posterior
into any particular diagnostic criteria. series of 146 patients with acute visual uveitis. Diligent monitoring of systemic
However, the idiopathic variety loss during pregnancy 49 of which were vitals, along with a team of specialists
included no exclusive posterior uveitis due to retinal and choroidal diseases. is needed to rule out eclampsia and
in this case series nor did they report This series has not grouped posterior hypertensive related issues as they
a new case in the puerperium period. uveitis in the form of choroidopathy can be life threatening. Due to the
separately and have probably clubbed possibility of MS, even detected in some
reports a decade later; we need to be vary
in the long term follow up and have
counselled the patient accordingly.

Although we treated our patient with
systemic steroids with a working
diagnosis of non-infectious posterior
uveitis with “probable VKH” (albeit at
minimum required doses), reports exist
of good outcomes of such cases after
no treatment or treatment with topical
medication only7. Could such cases have
improved primarily as a result of the
ameliorating effect of later pregnancy
and puerperium? What should be the
protocol for systemic steroids and its
tapering, if at all needed, in such cases?
Further studies will be needed to answer
these, albeit questions of ethics remains
for pregnancy related issues8.

References
1. Errera MH, Kohly RP, da Cruz

L. Pregnancy-associated retinal
diseases and their management. Surv
Ophthalmol 2013;58:127-42
2. Leiba H, Glaser JS, Schatz NJ, Siatkowski
RM. Postpartum optic neuritis: etiologic
and pathophysiologic considerations. J
Neuroophthalmol 2000; 20:85–8.
3. Park Y. J., Park K. H., Woo S. J. Clinical
features of pregnancy-associated retinal
and choroidal diseases causing acute
visual disturbance. Korean Journal of

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Subspeciality-Retina

Ophthalmology: KJO. 2017;31(4):320– 6. Rabiah PK, Vitale AT. Noninfectious Corresponding Author:
327. uveitis and pregnancy. Am J Ophthalmol
2003;136:91-8 Dr. Syed Faraaz Shahzad Hussain MS
4. Erkkilä, H., Raitta, C., Iivanainen, M. et Department of Ophthalmology, T.N.M.C
al. Graefe’s Arch Clin Exp Ophthalmol 7. Nohara M, Norose K, Segawa K. Vogt– & B.Y.L. Nair Charitable Hospital, Mumbai
(1985) 222: 134. https://doi.org/10.1007/ Koyanagi–Harada disease during Central, Mumbai, Maharashtra, India
BF02173537 pregnancy. Br J Ophthalmol 1995;79:94–
95
5. Weinstein L. Syndrome of hemolysis,
elevated liver enzymes and low 8. Chiam NPY, Hall AJH, Stawell RJ, et
platelet count: A severe consequence of al The course of uveitis in pregnancy
hypertension in pregnancy. Am J Obstet and postpartum. British Journal of
Gynecol. 1982;142:159-167 Ophthalmology 2013;97:1284-1288.

54 DOS Times - Volume 25, Number 3, November-December 2019 www.dosonline.org/dos-times

Basics

Contrast Sensitivity:
Essential, but Often Ignored

Obaidur Rehman, Parul Ichhpujani
Department of Ophthalmology, Government Medical College and Hospital, Chandigarh, India

Vision is not limited to the black and the same with various diseases has been mathematical formulas.
white of Snellen’s chart used to measure described by various authors. Studies Weber contrast is used when the
acuity. While the Snellen’s chart puts have shown that various conditions luminance of the background remains
up black alphabets against a white such as dry eye1, myopia2, age-related same.
background, it is not all where the ‘good macular degeneration (ARMD)3, Weber contrast = Luminance (object) –
vision’ ends. There are multiple objects glaucoma4, cataract5 and cerebral Luminance (background)
of varying sizes, colors and brightness lesions6-9 affect contrast sensitivity Luminance (background)
in our visual field and interpreting even in presence of 20/20 visual acuity. Michelson contrast is used when both
them clearly is a crucial aspect of Changes in contrast sensitivity can the light and component are varying.
vision. Even a patient with 20/20 on also occur after LASIK, PRK and other Michelson contrast = Luminance (max) –
Snellen’s chart may complain of having refractive surgeries10. Thus, contrast Luminance (min)
visual deficits such as differentiating sensitivity offers a measure of visual Luminance (min) + Luminance(min)
objects from their background. Misty dysfunction that is not attainable by An object can be displayed as varying
or blurred vision may be reported by conventional methods and ignoring number of lines with spacing between
such patients despite having 20/20 contrast sensitivity in many conditions them, and the number of alternately
Snellen acuity. Visual function has can be a great neglect on our part. This placed dark and lighter lines determine
multiple facets, and one of the most article will focus on the various tests the spatial frequency for any particular
important ones is Contrast Sensitivity. that have been used to measure contrast visual angle. So, a high spatial frequency
VA charts measures minimum angle sensitivity. will have densely packed lines while
of visual resolution using high contrast a lower frequency will have sparsely
targets only (18 to 24 cycles per degree Four parameters namely, peak placed lines.
[cpd]), however many real-world tasks sensitivity, peak frequency, bandwidth, Contrast Sensitivity Function (CSF):
are not performed in high contrast and and low-spatial frequency truncation, Contrast Sensitivity Function is
may be dependent on peripheral visual quantify contrast sensitivity. Peak the subjective measurement of an
function and low spatial contrast (3 to Sensitivity is the highest sensitivity individual’s ability to detect low
6 cpd). to luminance noted when contrast contrast pattern stimuli, i.e. it is
sensitivity is plotted against spatial indicative of sensitivity to various
Contrast is the difference in the frequencies tested, this peak is seen frequencies of light stimuli. A graphical
luminance of an object with it’s around values of 1-8 cycles per degrees plot of Contrast Sensitivity over a
surrounding background and the (cpd) of spatial frequency. The spatial range of spatial frequencies gives the
ability to appreciate this slight change frequency at which the highest Contrast Sensitivity Function. Normal
in luminance of two regions, not contrast sensitivity is noted is called contrast sensitivity function has a peak
separated by definite borders is Contrast the peak frequency. Different spatial sensitivity at about 5 cpd and a high
Sensitivity. frequency bandwidths also affect frequency cut-off at about 60 cpd.
contrast sensitivity; increase in contrast Neural mechanism of contrast: Three major
Contrast sensitivity deficits have a thresholds is seen with increasing
major impact on the quality of life. bandwidths as a larger part of contrast
As compared with acuity, contrast spectrum falls in areas of spatial
sensitivity correlates better with frequencies which are less sensitive in
target identification while walking, the visual system.
driving, and for facial recognition. The
importance of contrast and decrease in Contrast can be measured by various

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Basics

neural retinogeniculate pathways have Figure 1: Contrast Sensitivity Function plot. (Source: Zong Qin (2020). Contrast
been identified in modern studies that sensitivity function (Barten’s model) (https://www.mathworks.com/matlabcentral/
relay information from the retina to fileexchange/68784-contrast-sensitivity-function-barten-s-model), MATLAB Central File
the visual cortex – the magnocellular Exchange).
pathway (MC), the parvocellular
pathway (PC) and the koniocellular with the exception of Spaeth Richman for each level of contrast and asked to
(KC) pathway11,12. Each of these have Contrast Sensitivity Test (SPARCS), identify which of them has gratings
distinctive characteristics and are which also checks peripheral contrast and which is blank. End point is when
related to different aspects of vision. sensitivity. the subject fails to respond. This test
The MC pathway has high temporal is repeated 4 times and average score
frequency sensitivity, showing much I. Grating charts calculated.
more sensitivity to low spatial, high Hadi et al conducted a cross sectional
temporal frequencies. It is considered to a) Arden grating plates study in Iran involving 2,449 normal
be responsible for detection of contrast individuals with age range of 4-89 yrs
over a wide range of luminance. The One of the first contrast sensitivity and association of contrast sensitivity
PC pathway has a greater sensitivity for tests to come into common practice, it with age, gender and BCVA was
high spatial, low temporal frequencies involves the examiner uncovering a test studied. The study concluded that
and mainly involved in chromatic plate slowly and the subject reporting contrast sensitivity was higher in men
processing and visual acuity. when they are able to see the chart for than women (p<0.001)13. Pearson’s
the first time. It includes sine wave correlation coefficient showed that
Tests for Contrast Sensitivity gratings on 7 plates, with different contrast sensitivity score significantly
The first attempt at contrast spatial frequencies. Contrast decreases decreased with increasing age, lower
measurement dates back to 1760, when from top to bottom. BCVA, higher astigmatism and
French hydrographer Pierre Bouguer severity of myopia. Also, the score was
used 2 candles to cast shadow of a rod yy Drawbacks: It is not a forced choice significantly different in right, left and
on a screen to demonstrate that shadow test i.e. choosing yes/no and the both eyes between individuals with
of the rod cast by the distant candle on results depend on speed of exposure normal and decreased visual acuity.
a white screen remained visible until of plate. The relationship between contrast
this distant candle was more than seven sensitivity and gender according to
but less than eight times as far removed b) Cambridge grating plates Cambridge test was later proved to be
from the screen as a nearer candle just controversial and other results were
one foot away from it. This test has 12 pairs of plates and contradictory, thus the test was not
employs square wave gratings for
Almost 100 years later, interest testing. It is performed at a distance of
again resurfaced regarding contrast 6 metres, the subject is shown 2 pages
sensitivity. In 1845, Masson used a
spinning disc, which was white in
colour, with a black sector marked
on it. When it was spun quickly, a
grey ring was produced with contrast
proportional to the width of the black
sector.

Many researchers over the years have
since experimented with various
resources to understand and quantify
contrast sensitivity as a visual function.
Central contrast sensitivity can be
evaluated from the central area of retina
corresponding to macula and peripheral
contrast sensitivity by evaluating extra
macular areas.

We discuss a few tests that have been
used in modern times. Most tests
check only central contrast sensitivity

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Basics

used in later studies. units) and an alternative forced choice spatial contrast sensitivity. These
method, presumably to try to improve cards contain horizontal square wave
Drawbacks: As it contains only 2 choices, repeatability. gratings of very low spatial frequency,
a high probability of correctly guessing with a three cycle grating.
exists. Additionally, FACT has “blurred”
grating patch edges with the gratings 22x20 cm gratings are present either
c) Vistech Contrast Sensitivity Chart smoothed into a grey background with on the right or the left half side, with
a larger patch size so that an increased a 3 mm peephole in the centre and the
Vistech Charts come in various versions, number of cycles can be presented at patient has to look at the side which
wall chart version is VCTS 6500 and the low spatial frequency. has the grating. Used along with Teller
vision screener based version is MCT- acuity cards, Ohio cards test contrast in
8000. Drawbacks: The smaller step size with a range from 96% to 1%. This test has
same number of steps results in a shown promise in low vision patients
It is performed at 10 feet distance, for 5 smaller range of scores for the FACT who have difficulty in recognising
spatial frequencies(spatial frequencies chart compared to the Vistech, so a optotypes and may be utilised to
1.5, 3, 6, 12 and 18 (cpd), having 9 ceiling effect is created. Studies have prognosticate the patient regarding his
levels of contrast (columns) for each shown low test-retest reliability even everyday chores.
frequency., The average step size is with FACT.
about 0.25 log units with a range of 1.75 i) Berkeley Discs
log units. The gratings are either vertical f) Lea Grating Test
or tilted 15° to the right or left. Subject Another novel test for pediatric contrast
is asked to identify orientation of sine This test has been employed for testing sensitivity, it employs 3 double sided
wave gratings as vertical, diagonal in children 3 months to 36 months plastic cards with randomly arranged
left or diagonal right from circular in age. Various grating paddles are discs of 5 cm size on each side in a grid
photographic plates. available with stimuli being 1,2,4 and of six 7.5 cm cells. 3 discs are printed on
8 cycles per centimetre(cpcm), and the card, with 0.60 log unit difference
Drawbacks: Non uniform decrease in the measurement is determined by and the patient is asked to detect the
contrast levels (step sizes are irregular) movement of the child’s eyes. Testing is presence of discs on the cards at a
and high chance of correctly guessing started off with the coarsest grating and distance of 40 cm. If a patient fails to
as only 3 choices available. These charts then successive gratings are shown to detect the presence of disc, examiner
have been shown to have poor test the child. Threshold of visual contrast moves to corresponding disc on the
retest variability. is defined by the last paddle which second card, which has a unit value
receives a positive response from the of the nearest 0.15 log units. Contrast
d) Vector vision CSV-1000 child. testing is performed from 100% to 1.1%.

It has circular photographic plates, g) Hiding Heidi test j) Letter Charts
like Vistech and testing is performed
at 8 feet distance. 4 spatial frequencies It employs smiling cartoon faces for low A) Regan low contrast chart
are tested, having 9 levels of contrast contrast testing in children and adults
for each frequency. Subject is shown who are unable to speak. A card with a Test consists of three different charts
2 photographic plates and asked to smiling cartoon face is hidden behind a for contrast levels of 96%, 7% and 4%.
identify the one with gratings on it. This white blank card and the child’s response Testing is performed at 3 metre distance,
test has an advantage over other tests in is assessed with exposure of the cartoon with 8 letters in one line. As the patient
having internal illumination, which face. Cards are exposed in decreasing reads from top to bottom, each row of
negates uneven lighting problems. levels of contrast: 100%, 25%, 10%, letters decreases in size and contrast
5%, 2.5% and 1.25%. Responses such as level. Number of letters read correctly
Drawbacks: Having only 2 choices eye movements towards card, smiling, per line are noted.
creates a high chance of correctly head turning and pointing are recorded
guessing the answer. as positive responses. Along with Lea Regan demonstrated that these charts
gratings, this test provides a useful tool had a role in early vision loss detection,
e) Functional Acuity Contrast Test in clinical setting for infants and pre- especially in diabetics and glaucoma
(FACT) verbal children. patients14.

This test is a modification of Vistech h) Ohio Contrast cards Drawbacks: Unequal spacing between
(second generation), therefore, the basic letters is present. For smaller spatial
testing principle is same as Vistech. They have been utilised in patients with frequencies(larger letters), contrast
FACT uses a smaller decrease in contrast low vision for measuring maximum levels are too easily tested and do not
at each level of contrast (0.15 log

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Basics

reach the contrast threshold levels. Figure 2: Pelli Robson Chart. according to the possible positions
Also, it cannot be performed in illiterate of the Landolt-Cs’ slit. Measurement
patients. 1.92 log contrast and for individuals terminates after a fixed number of trials.
older than 60 years is 1.52-1.76.15. To estimate the acuity threshold, a best
B) Pelli Robson chart PEST (best Parameter Estimation by
Drawbacks: Uneven lighting and Sequential Testing) procedure is used in
Most commonly used contrast inability to perform test in illiterate which a psychometric function having
sensitivity detection tool. Testing done patients are the chief drawbacks. a constant slope on a logarithmic acuity
at 1 metre distance, on a chart with scale is assumed.
Sloan letters arranged in 16 triplets. III. Computer based tests
Each row has two triplets i.e. 6 letters B) Holladay automated contrast
of same size, with contrast decreasing Offer several advantages and sensitivity system
from left to right. Each triplet fades by disadvantages over non-computerised
0.08 log units (Figure 2). A subject needs tests. It employs concentric rings of different
to identify atleast 2 letters of a triplet frequencies, like a Bull’s eye displayed
for crediting score for that particular Advantages include display of targets on a blank screen. When a subject gives
triplet. Subject able to read the faintest in random patterns, thus avoiding an incorrect response, smaller steps are
triplet is recorded and score is given recall, ability to alter levels of contrast, used to bracket contrast threshold.
as logarithmic contrast value for that may be used even for illiterate patients
triplet. and can be accessed at any place with a C) Spaeth Richman Contrast
computer. Sensitivity test (SPARCS)
Norms for different levels of contrast
loss are Normal, when the patient can Recently, innovative pixel dithering It is a novel internet-based test, testing
read 6-7 lines (12-14 triplets). Moderate techniques have enabled gratings based both central as well as peripheral
contrast loss is based on the patient only testing possible on mobile tablets, too. contrast threshold for a subject, using
being able to read 4-5 lines. Severe loss is vertical square wave gratings with
when the patient can only read 2-3 lines Drawbacks: The cost of computer, a spatial frequency of 0.4 cycles per
and profound contrast loss is when the variable size and brightness of computer degree. It can be accessed at https://
patient can only read 1 line or less. screens and time consuming nature of www.sparcscontrastcenter.com.
the tests may be deterrent.
Drawbacks: Uneven lighting, reflection The range of contrast tested is from
from surface and inability to perform A) Freiburg Visual Acuity and 100% to 0.45% (log CS 0.00 to 2.35) and
test in illiterate patients. Contrast Test (FrACT) decreases by approximately 0.15 log
units between levels. The contrast value
Moreover, the chart has only 2 versions FrACT is an automated test in which is calculated by Weber contrast.
with different triplets of optotypes. Landolt-Cs are presented on a monitor
Patients may recall letters with frequent in one of eight orientations. The subject Five areas are tested, in which gratings
use, especially those letters that are presses one of eight buttons, which are appear for 0.3 second in a random
found around their threshold. spatially arranged on a response box manner. Correct and incorrect
responses are recorded until contrast
C) Mars test threshold is determined for each area,
using staircase strategy with reversals.
It is similar to the Pelli Robson test, Initial correct responses advance four
in using Sloan letters but the chart is levels until an incorrect response is
much smaller in size. Testing is done made. After the incorrect response,
at a distance of 50 cm and contrast the contrast level presented is two
decreases by 0.04 log units between levels easier. Thereafter, the algorithm
adjacent letters as the subject reads. advances or regresses one level at a time
Test ends when there is failure to read until two incorrect responses are made
two consecutive letters. Due to its at a specific level, which establishes the
smaller size, testing and storage is more threshold. The test defines consecutive
convenient than Pelli Robson chart. clicking on the same quadrant more
than 4 times as a refusal to guess, in
Norms for different levels of contrast which case the test is automatically
loss include profound loss at less than terminated, no score given, and an
0.48 log contrast, severe at 0.52-1.00, explanation provided before retesting.
moderate 1.04-1.48. Normal value for
individuals age 60 and younger is 1.72-

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Figure 3: Result of SPARCS at the end of the test, with total resolution score and respective to match the boundary of the targets
scores of each area. that can be seen. This test, in addition
to being time efficient allows plotting
Figure 4: Detailed response detail of all areas displayed at along with the scores at the end of results and testing over a wide range
of SPARCS test. of frequencies but carries the drawback
of having lower repeatability than the
The log-based score of each of the 5 several years, found that SPARCS scores Pelli Robson test and also the need for
testing areas is scaled out of 20, making were one of the best predictors of which expensive equipment.
a maximum SPARCS score of 100 glaucoma patients were at highest risk
(Figures 3 and 4). SPARCS scores in of progressing rapidly17,18. Conclusion
individual areas can be converted to log D) Aston Contrast Sensitivity test Various tests for contrast sensitivity
CS using the equation: log CS score = This is a mobile application for near evaluation are available, each with
(SPARCS score * 2.346353) / 20. and distance contrast sensitivity test, advantages and drawbacks of its own.
Total SPARCS scores can be converted displaying all contrasts and frequencies With the advent of computer based
to log CS using the equation: log CS using swept frequency, onto a LCD testing, more convenient, accurate and
score = (SPARCS score * 2.346353) / 100. monitor screen19. Designed for the iPad simpler means for contrast evaluation
Studies show that contrast sensitivity, (Apple Inc., Cupertino, California, USA), can be looked upto, which can cross
which SPARCS measures, correlates it is a novel time efficient test with good language and literacy barrier18.
with Quality of Life and people’s actual repeatability. For near testing, patients
ability to perform activities of daily are shown gratings on the screen and Contrast sensitivity evaluation gives
living better than visual field, visual asked to trace the boundary of the same, a more meaningful idea of visual
acuity, stereopsis, and IOP16. allowing CSF detection. For distance function than visual acuity alone can
Waisboard et al. prospectively testing, a monitor controlled by the iPad provide. Contrast sensitivity testing
monitored glaucoma patients over displays swept frequency targets and the helps to predict illumination, contrast
patient moves sliders on the iPad screen & magnification needs and thus helps
in predicting success with optical
devices. Loss of contrast sensitivity is
not specific for a particular diagnosis
but can give clues for identifying ocular
disease and guiding further treatment.

References
1. Szczotka-Flynn LB, Maguire MG, Ying G,

et al. Impact of Dry Eye on Visual Acuity
and Contrast Sensitivity. Optometry and
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and contrast sensitivity in patients
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14. Regan D, Neima D. Low-contrast letter Corresponding Author:
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spectral coding in primate retina. Annu Glaucoma. JAMA Ophthalmol. 2015

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Keratoconus

Farin Shaikh MD, Prafulla K. Maharana MD, Ritu Nagpal MD
Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India.

Keratoconus (KC) is a disorder • Atopy- Bronchial asthma, Corneal thinning: The thinnest part of
characterized by progressive corneal angioneurotic edema, Marfan the cornea located outside the visual
steepening (usually asymmetrical non syndrome axis is a common sign preceding ectasia.
inflammatory), most typically inferior Thinning is most commonly seen
to the center of the cornea, with eventual • Mitral valve prolapse inferiorly or infero-temporally.
corneal thinning, induced myopia, and • Rosacea
irregular astigmatism. It is the most Clinical Features Corneal ectasia: An eccentrically located
common corneal ectatic disorder seen ectatic protrusion of the cornea is noted
in clinical practice. Prevalence of KC • Symptoms: A case of KC can present in KC. The apex is usually inferior to a
is about 54.5 cases per 100 0001-3. KC with following symptoms horizontal through the pupillary axis.
occurs in people of all races. There is • Progressive visual blurring and/
no significant gender predilection. KC or distortion- due to associated Corneal scarring: usually sub-epithelial.
usually occurs bilaterally. Unilateral irregular astigmatism. It may be (Figure-1).
cases occur can occur but rare (in the associated with Photophobia,
range of 2–4%). The age at onset is glare, monocular diplopia, and Fleischer ring- a partial or complete
usually at about the age of puberty. The ocular irritation annular line commonly seen at the base
disease has a rapid progression stage • Frequent change of glasses- the of the cone. This line is nothing but a
until the age of 30 years. The rate of irregular astigmatism is often hemosiderin (Iron deposits) arc or circle
progression plateaus after this. After the difficult to correct with glasses line seen around the cone base. This ring
age of 40 years the disease progression hence the patient keeps on is brown in color and best appreciated
usually stops. It is more prevalent in visiting different optometrist. with the cobalt blue filter using a broad,
the Asian countries than in the West. • Rarely a case may present with oblique beam (Figure-2).
Asian patients presents at a younger age symptoms of associated diseases
compared to the western world. such as recurrent attacks of Vogt’s striae: These are fine vertical lines
itching, eye rubbing (vernal produced by compression of Descemet’s
Etiology keratoconjunctivitis) and KC is membrane, which tend to disappear
Largely idiopathic. Can be associated discovered during examination. when physical pressure is applied on
with ocular and systemic associations. • Signs: following signs can be seen the cornea digitally or by gas permeable
Ocular allergy is a common association in a case of KC depending upon contact lens wear. The lines are seen
in India. the stage of the disease1,4-7. in the deep stroma and Descemet’s
• Mild cases. membrane and are parallel to the axis of
o Ocular associations the cone.
Scissoring of the red reflex on
• Floppy eyelid syndrome retinoscopy Prominent corneal nerves: The increased
• Leber’s congenital amaurosis visibility of corneal nerves increased
• Cone-rod dystrophy Charleux sign: With a dilated pupil results from the outward bowing and
• Corneal granular dystrophy and a lens + 6 D positioned in front thinning of the ectatic cornea (Figure-3).
• Vernal keratoconjunctivitis of the eye one can appreciate a dark
• Refractive surgery reflex in the area of the cone with a Increased intensity of the corneal endothelial
• Trauma central bright reflex resembling a drop reflex: An endothelial reflex may appear
o Systemic associations: of honey or oil (sign of “Charleux”), in at the peak of the cone due to the
the reflection of the red bottom from a increased concavity of the posterior
• Down syndrome direct ophthalmoscope. corneal surface.

• Moderate to Severe Cases Sub-epithelial fibrillary lines: Bron et al has
described, white subepithelial fibrillary
lines in concentric bundles lying just

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Figure-1: A case of KC with corneal ectasia and thinning (red arrow) Figure-2: Fleischer ring as seen with cobalt blue filter on slit-lamp
and sub-epithelial scar (white arrow). examination.

Figure-3: Slit-lamp photograph showing Vogt’s striae (white arrow) Figure-4: Rizzuti phenomena (red arrow).
and prominent corneal nerve (red arrow).

inside the Fleischer’s ring1. These are Normally the light rays illuminate the index-based systems.
best seen under high magnification nasal limbal area (Figure-4).
with a broad, oblique slit beam. The Munson Sign: anterior bowing of lower Morphological classification:
pattern is characteristic of KC and lid on downward gaze of the patient Classically, KC has been classified into:
occurs in approximately one-third of (Figure-5).
patients with this disease. Corneal Hydrops: Breaks in Descemet’s • Nipple- the cone has a diameter
membrane have been described in <5mm, round morphology and is
Corneal hyperesthesia can be detected severe KC, causing acute stromal edema, located in the central or paracentral
early in the course of the disease. known as Hydrops, sudden vision loss cornea, more commonly in the
Later the cone becomes relatively less and significant pain (Figure-6). infero-nasal corneal quadrant.
sensitive. Correction with contact lenses is
Classification/Grading normally relatively easy.
• Advanced Stages KC is classified based on morphology,
Rizzuti phenomena: This is demonstrated disease evolution, ocular signs and • Oval- The cone has a diameter >
by a penlight shining on the temporal 5mm and a paracentral to peripheral
side of cornea or to the iris plane. location, more commonly in the
infero-temporal corneal quadrant.

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Figure-5: Anterior bowing of lower lid (white arrow). Figure-6: Diffuse corneal edema in corneal hydrops

Amsler-Krumeichs classification of Keratoconus the change in keratometry. However,
progressive deterioration of BCVA,
Stage Description progressive decrease in corneal
thickness and a previously CL tolerant
1 Eccentric corneal bulging patient becoming CL intolerant are
Myopia and/or astigmatism < 5D certain other clinical clues of KC
Corneal radius ≤ 48D progression. Following history must be
Vogt’s striae recorded carefully
No central opacity
• Contact Lens (CL) wear- Its role in
2 Myopia and/or astigmatism > 5D but < 8D KC progression is controversial. A
Corneal radius ≤ 53D better best-corrected visual acuity
No central opacity (BCVA) with CL indicates good
Pachymetry ≥ 400μ prognosis after keratoplasty.

3 Myopia and/or astigmatism > 8D but < 10D • Eye Rubbing- Mechanical epithelial
Corneal radius > 53D trauma leads to release of cytokines
No central corneal opacity that have a role in corneal
Pachymetry 200- 400μ weakening and ectasia.

4 Refraction not possible • Topography- the patient might
Corneal steepening >55.00 D have been already a case of
Corneal scarring diagnosed KC and a serial recording
Pachymetry <200μ of the keratometry, central corneal
thickness (CCT), and thinnest
Contact lens correction is more (ii) Moderate- 45-52 D pachymetry must be done. An
difficult. (iii) Advanced- >52 D increase in keratometry by 1 D
• Globus - The cone is located (iv) Severe- >62 D over a period of one year suggests
throughout 75% of the cornea. progression and such cases require
Contact lens correction is a difficult Work-Up CXL (few clinicians consider an
challenge, except in very limited History: The onset and progression of increase of 0.5D per 6 months).
cases. the disease is characteristic. The onset
Disease Progression: Amsler proposed is usually at puberty. It is important to • Ocular surgery- KC can occur
the first KC classification based on the know whether the KC is progressive or secondary to ocular surgeries such
disease evolution2. not. In case of progression, the patient as LASIK, Radial Keratotomy (RK).
can be advised to undergo corneal Hence, any past refractive surgery
Curvature: KC is classified into following collagen crosslinking (CXL). The best must be enquired. In few cases, a
way to document progression is serial previous history of CXL may be
(i) Mild- <45 D topography taking into consideration

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Differential Diagnosis

Characteristics KC PMD Keratoglobus TMD
Less common Rare Rare
Frequency Most common Bilateral Bilateral Bilateral

Laterality Usually 20 to 40 years
bilateral Inferior band 1 to 2 mm wide

Age at onset Puberty Usually normal Usually at birth Middle-aged to elderly
Superior to band of thinning
Thinning Inferior Maximum in periphery Superior cornea
paracentral Absent

CCT Reduced Sometimes May be normal Usually normal
Only after hydrops Generalized Superior cornea
Protrusion Thinnest at
apex

Rizutti’s phenomenon Present Present Absent
Munson’s sign

Fleischer ring Present None Absent
Mild Superior cornea with
Scarring Common Vascularization,
Sometimes Lipid deposition and
Vogt’s Striae Common Sometimes Inflammation
Absent

Pentacam parameters for diagnosis of early KC/FFKC Eyelid: look for signs of allergic
Findings on the sagittal map conjunctivitis. In advanced KC
Central K-readings ³ 48 D Munson’s sign, a V-shape deformation
SRAX ³22° of the lower eyelid when the eye is in
Superior–inferior difference (S-I) on the 5 mm circle ³ 2.5 D downward position can be elicited.
Inferior–Superior difference (I-S) ³ 1.5 D Conjunctiva: Look for presence of
Corneal astigmatism ³ 6D papillae in tarsal conjunctiva. In
Findings on the thickness map India, KC is often associated with
Thinnest location < 470 m VKC or allergic conjunctivitis. Signs
Y co-ordinate value of the thinnest location ³500 m of VKC include papillae, Trantas dots
Pachymetry apex – thickness at thinnest location ³ 10 m (gelatinous thickening of limbus),
Superior–inferior at 5 mm circle ³ 30 m limbal nodule, pigmentation and ropy
Difference in thickness between both eyes at thinnest locations ³ 30 m discharge.
Findings on the elevation maps Cornea: Look for the various signs as
Isolated focal island of ectasia (BFS mode) on either surface described under signs.
Values ³ 12 m within the central 5 mm on the anterior elevation map (BFTE mode) Fundus examination: Fundus evaluation
Values ³ 15 m within the central 5 mm on the posterior elevation map (BFTE after mydriasis is essential for any
mode) concomitant fundus abnormality.
Investigation
there. Examination Keratometry: Keratometry mires in KC
• Past medical history- KC can be Visual acuity: Uncorrected visual acuity are commonly steep, highly astigmatic,
and BCVA must be assessed in all cases. irregular, and often appear egg-shaped
associated with certain ocular Refraction must be attempted in all (rather than circular or oval). The
and systemic disorders. A careful such cases. disadvantages of keratometry in KC is,
history must be taken to rule out Facial appearance/Orbit: Look for sign it provides information about central
these disorders. of orbital fat atrophy/oculo-digital 3 mm of cornea only, it is not useful in
• Family history: Between 6%-18% phenomena suggestive of chronic eye irregular astigmatism.
of patients with KC have a positive rubbing.
family history.

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Table: OCT Classification of Keratoconus was possible with earlier devices and
thus extremely useful in the proper
Stage Features Other features diagnosis of peripheral diseases such as
pellucid marginal corneal degeneration
Stage 1 Thinning of epithelium and An annulus of thickened epithelium (PMCD). It is an extremely useful tool
stromal layers at the cone is seen surrounding the thin for diagnosis of early KC. The different
epithelium at the cone giving the pentacam values that help in diagnosis
characteristic “doughnut pattern” of FFKC are summarized in table below9.

Stage 2 Hyperreflective anomalies Variable amount of stromal opacities Anterior Segment OCT: Fourier-domain
at the Bowman’s layer level optical coherence tomography (OCT)
with a thickened epithelium can be used for examination and
at the cone measurements of different layers in
a few seconds. It can map the corneal
Stage 3 Posterior displacement Variable amount of stromal opacities epithelium thickness, facilitating
of the hyper-reflective early KC detection. In addition, it is
structures occurring at extremely useful in assessing the depth
the Bowman’s layer level of scar and hence to decide upon the
with increased epithelial type of surgery. Another important use
thickening and stromal of ASOCT is diagnosis and management
thinning of corneal hydrops as it can accurately
show the area of DM tear and location of
Stage 4 Pan-stromal scar Thickened epithelium compensates fluid pockets in the cornea. A new OCT
for the stromal thinning. classification for KC has been proposed
based on structural corneal changes at
Stage 5 Hydrops- large intrastromal 5a, acute onset: Descemet’s the cone during the evolution of the
cysts communicating membrane rupture and dilaceration disease. This has been summarized in
with anterior chamber of collagen lamellae with large fluid- table below in table. This classification is
through a tear in Descemet’s filled intrastromal cysts useful in advanced cases of KC in which
membrane 5b, healing stage: Total corneal the repeatability of corneal topography
scarring with a remaining aspect of measurements are not reliable10.
Descemet’s membrane rupture
Corneal biomechanics in KC
Pachymetry: both ultrasonic and optical Placido-disc based imaging
based principle (ASOCT) can be used to [Videokeratography (VKG)]: It provides The current concept for KC is that
measure the pachymetry. Measurement qualitative contour information. In there is a focal area of weakening in
of corneal thickness is useful for early cases, there will be an isolated area corneal structure to begin with. Various
diagnosis, documenting progression, of smaller ring spacing and distortion. environmental and other factors such as
and planning treatment (see treatment As the KC worsens, the cornea becomes atopy, eye rubbing starts a chronic cycle
section). steeper; the ring spacing decreases of biomechanical weakening that leads
Imaging in KC overall and becomes increasingly to localized thinning and steepening,
The diagnosis of moderate to severe KC, irregular. Its disadvantage is it does which ultimately culminates in KC11,12.
clinically, is straightforward. The role not give accurate information about Thus, earliest changes to KC corneas
of imaging in modern era is primarily posterior curvature (can not detect can be detected by in vivo assessment of
in identifying mild and forme fruste KC early KC) and corneal thickness. corneal biomechanics. Currently, there
which are known risk factors for post are two commercially available devices
LASIK ectasia, detecting progression Scanning slit based imaging (Orbscan): for in vivo characterization of corneal
of KC especially when collagen cross- It provides reliable data on anterior biomechanics i.e. Ocular Response
linking is an option for arresting and posterior elevation and best-fit Analyzer (ORA; Reichert Ophthalmic
progression and to differentiate KC sphere and a corneal pachymetry map. Instruments, Buffalo, NY) and Corvis ST
from other form of corneal ectasia8. The However, the posterior curvature maps (Oculus, Wetzlar, Germany). Although
different corneal imaging modalities are based on assumptions and may different studies have tried to evaluate
commonly used are described below. not be 100% accurate. Scheimpflug biomechanical response, with majority
Pentacam and spectral domain OCT are imaging (Pentacam/Oculyzer/Galilei)- on ORA, it is difficult to recommend
the most commonly performed imaging It provides reliable measurement of precise guidelines. The various factors
modalities for KC. anterior and posterior corneal elevation for this being, a wide variability in
and accurate measurement of corneal
thickness. It also covers significantly
more of the cornea in periphery than

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normative data among different Comparison of DALK and PKP
population and secondly, overlapping
of parameters between normal and Parameter DALK PKP
abnormal corneas. Both endothelial failure and
Indication Stromal opacification with stromal opacification.
From current evidence, it seems healthy endothelium Delayed
waveform-derived parameters that
describe corneal deformation through Visual Early Best
specific waveform features such as rehabilitation None
the width, peak area, and height of the Less
peaks) in ORA and radius of curvature Quality of vision Poor than PKP
at highest concavity or inverse concave More
radius in Corvis ST, are the parameters Interface haze Affects vision
that may turn out to be useful in early Poor
cases of KC in future. Higher order More Risk of expulsive hemorrhage
abberations
The other major use of corneal Complications can occur
biomechanics could be evaluation of Post-op Less
biomechanical changes in KC with Astigmatism Poor
different management techniques Prolonged
such as CXL or keratoplasty. This may Wound strength Better Only optical grade
allow us to know the efficacy of the
various procedures. Postoperative ORA Open sky None Not possible
assessments have shown that following procedure
DALK, corneas achieve biomechanical High risk
metrics similar to those of normal Intraocular None Easy
corneas while PKP treated corneas surgery Less steep
could not achieve the same. Similarly,
experimental CXL studies have Tensile strength Better
reported corneal stiffness increases
about 300 % following CXL suggesting Steroid use Early taper
its efficacy in halting the progression.
[11,12] However, as discussed earlier, Donor criteria Not stringent even non-
changes in corneal stiffness could not optical grade can be used
be properly validated in in vivo studies
and further research is needed in this Single donor Possible
field. multiple use

Management Graft rejection Low risk
The treatment of KC management
varies depending on the disease severity. Technique Difficult
Early case is managed with spectacles,
mild to moderate case are managed Learning curve Steep
with contact lenses, and severe case
can be treated with keratoplasty. Other visual acuity cannot be achieved to sit, whereas the gas permeable
surgical treatment options include with this type of visual correction. contact lens is primarily used
intra-corneal rings segments, corneal for providing adequate visual
cross-linking, intra-ocular lens implants • Contact lens: Different contact lenses acuity. Hybrid contact lenses
or a combination of these. used for treatment of KC are soft (such as SoftPerm, Solotica and
toric lenses, standard bicurved hard Synergeyes) contain an RGP center
Non-Surgical management lenses, custom-back toric lenses, with a soft skirt. New-generation
piggyback systems, hybrid lenses hybrid CL provides higher oxygen
• Spectacles: Spectacles are normally (made of combined hard lens with permeability and greater strength of
used in early cases of KC only. As a soft skirt), scleral lenses, and mini- the RGP/hydrogel junction. Rose K
the disease progresses, irregular scleral lenses. Rigid gas permeable Lenses (Rose K, Rose K2 XL and Rose
astigmatism develops and adequate lenses: Rigid gas permeable (RGP) K2 IC) are multicurve lenses with a
corneal lenses are the lenses of small optical zone that snugly fits
first choice for correcting the over the cone. Scleral Lenses rest
irregular astigmatism. The three- on the sclera and do not touch the
point touch fitting technique is the cornea and limbus, leaving a clear
most popular technique. Piggyback area between the CL and the cornea.
systems consisting of the fitting The advantages are good centration,
a gas permeable on top of a soft stability and improved VA.
contact lens. The soft contact lens Surgical management
is used to improve wearing comfort
and provide a more regular area for Current surgical options include:
the gas permeable contact lenses

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• Corneal transplantation: acuity, contact lens tolerance and delay covalent bonds between collagen fibrils
Penetrating keratoplasty, Deep the need for corneal graft. It acts by its in the corneal stroma. The irradiation
anterior lamellar keratoplasty Arc-Shortening effect. It is commonly level at the corneal endothelium, lens
used to treat mild to moderate cases of and retina is significantly smaller than
• Intra-corneal ring segment insert: KC, as normal corneal transparency and the damage threshold. It has been
Intacs, Ferrara Rings a minimum corneal thickness of 450µm recommended not to perform this
at the site of the incision are required. technique in corneas thinner than
• UVA / riboflavin corneal cross 400µm as toxic reactions could take
linkage (CXL) Three types of rings are available: Intacs place in the corneal endothelium. In
which have a hexagonal cross-section such cases hypotonic CXL have been
• Lenticular refractive surgery: and are placed more peripheral than tried with variable success.
Refractive lens exchange with toric Ferrara Rings which are triangular /
intraocular lenses, Toric phakic prismatic in shape. Recently, Intacs SK CXL is largely safe except the risk
intraocular lenses (SK-severe KC) has been introduced of keratitis. No long-term problems
for use in more severe forms of corneal in terms of loss of transparency of
Penetrating keratoplasty (PKP): PKP in ectasia. It has two significant design the cornea or lens have occurred
KC in comparison to other indications modifications-a smaller inner diameter and endothelial counts have been
is considered low risk in terms of of 6.0 mm compared with 6.8 mm of the unchanged postoperatively. In addition,
graft rejection, graft survival and standard Intacs; and an elliptical cross this technique has been successfully
postoperative complications. The section compared with a hexagonal used in combination with other surgery
success rate is 90-95%. Visual recovery cross section of the standard Intacs. techniques, such as corneal rings
takes several weeks / months, with full segments.
stabilization not occurring until a year, The rings are inserted into the posterior
after which time the sutures can be stroma (about 75% of corneal depth at Refractive lens exchange: Refractive lens
removed. the incision site) in a quick outpatient exchange and toric phakic intraocular
technique performed under topical lens insertion may be of some benefit
In keratoconic eyes, the corneal anesthesia. The circular intra-lamellar in correcting myopia and astigmatism
endothelium is usually intact; with pockets for the rings are created in selected eyes with early/mild/stable
good cell counts even after cases of acute either using a specially designed disease with good spectacle corrected
hydrops, hence DALK is the procedure vacuum lamellar dissector or with the visual acuity.
of choice. The major disadvantage is femtosecond laser. Intra-corneal ring
corneal stromal rejection and migration technology does not offer a cure for the Key Points
of host keratocytes to replace donor condition but can very often produce a • VKC is an important risk factors for
keratocytes resulting in recurrence of marked improvement in unaided and
the disease in graft. However, stromal best corrected visual acuity and allow KC in India
rejection can never lead to graft failure eyes to be corrected with spectacles and • KC can present early in association
and recurrence in graft is extremely / or soft rather than rigid lenses.
rare. with VKC
Corneal collagen crosslinking with • CXL is effective in halting
The goal of DALK is to achieve a depth riboflavin (C3R) or corneal cross linkage
of dissection as close as possible to DM. (CXL): CXL using riboflavin (vitamin progression of KC
Various agents have been used to create B2) / ultraviolet A (UVA) [370nm] light • Most patients can be rehabilitated
a plane of separation between DM and is a therapeutic modality that can halt
the deep stromal layers. These include and stabilize the keratoconic process. using RGP contact lenses
air, fluid, viscoelastic, microkeratome It increases the corneal rigidity and • DALK is the surgical procedure of
and a femtosecond laser. The common biomechanical stability. The success
techniques of DALK are: Layer-by-layer rate varies between studies but over all choice
manual dissection, Air-assisted DALK 60-70% cases shows some stabilization References
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8. Matalia H, Swarup R. Imaging modalities Implications. Open Ophthalmol J. 2017
in Keratoconus. Indian J Ophthalmol

68 DOS Times - Volume 25, Number 3, November-December 2019 www.dosonline.org/dos-times



70 DOS Times - Volume 25, Number 3, November-December 2019 Orbital Implants

Anophthalmic Socket Orbital Fracture Tearsheet

Non Integrated Semi Integrated Integrated ALLOPLASTIC IMPLANTS
No integration with orbital Indirect (mechanical) Direct integration with the Porous polyethelene implant,
structures or with prosthesis. integration of the synthetic orbital structures with or Titanium mesh, Teflon, Silicone,
Neither allow ingrowth of implant with the orbital without integration with the PMMA,Tantalum,ePTFE,
granulation tissue nor have structures but not with the prosthesis. Allows Hydroxyapatite
preformed attachements for EOM. prosthesis. biointegration (fibrovascular
growth into the implant). AUTOLOGOUS MATERIALS
Calverium, Iliac crest , Ribs
Advantages -Cheap, easily available -Better motility -Increase success rate
-Smooth surface -Allow attachment of -Reduce implant COMPOSITE IMPLANTS
-Least complication rates extra ocular muscles in migration and extrusion Porous polyethylene & titanium mesh
-Can attach EOM if the tunnels on their -Permit better movement HA-reinforced high-density composite
wrapped with sclera anterior surface of overlying prosthesis (HAPEX)
BMP-2-loaded gelatin sheet with a
Disadvantages -Irregular anterior surface -Higher exposure rates biodegradable PLA based foil
-Discomfort and rates of -Costly
-Higher chances of migration erosion and extrusion are
high
-Special customised
prosthesis are needed to fit
its shape

Examples PMMA(Mules) Allen, Iowa,Universal, Porous Polyethylene, RESORBABLE IMPLANTS
Silicone Castervijo Hydroxapatite, Polydioxane(Ethysorb), Poly glycolic acid,
Bioceramic (Al2O3) Poly(l/DL lactide),
Wrapping of Implants Advantage Resorbable PLLA/PGA mesh plate
 Non porous – Precise recti Disadvantage (lactosorb® ),
 Autologous - Temporalis fascia, Barrier to vascularisation Polyglactine 910/PDO implants
auricular muscle attachment Increased cost of the procedure
www.dosonline.org/dos-times  Porous – Lesser Exposure Risk of transmission of prion-like
 Donor - Sclera, fascia lata, pericardium diseases.
 Polyglactin mesh, Acellular dermis rates No evidence of increased motility

Sahil Agrawal MD1, Deepsekhar Das MD1, Saloni Gupta MS2, Prof. M.S. Bajaj1
1. Oculoplasty and Paediatric Ophthalmology Services, Dr Rajendra Prasad Centre for Ophthalmic Sciences,
All India Institute of Medical Sciences, New Delhi, India.
2. Department of Ophthalmology, Northern Railway Central Hospital,Connaught Place, New Delhi, India.

DOS Sports Day & Picnic

Make Fitness a lifestyle choice for a Day!

Date: 1st March 2020 (Sunday), Time: 10:00 AM - 4: PM

Venue: Rashtriya Swabhiman Khel Parisar
(Near Pitam Pura TV Tower) Pitam Pura, New Delhi

www.dosonline.org/dos-times DOS Times - Volume 25, Number 3, November-December 2019 71