Chapter 3 Released

Gonioscopy

Gonioscopy is a bio-microscopic technique of examining the anterior chamber angle of the
eye with a contact lens known as the gonioscope.

Principle of Gonioscopy

The light emanating from the iridocorneal angle is not visible in the normal cornea because it
undergoes total internal reflection at the cornea air interface. The critical angle of cornea-air
interface is 46 degrees. A gonioscope lens obliterates this angle and allows passage of light
from angle to outside, making angle structures visible (Figure 1 & 2).

Figure 1: Total Internal reflection at the cornea- air Figure 2: Light coming from angle can be seen
interface of light travelling from angle. reflected from gonio mirror as goniolens obliterates the
cornea air interface.

Types of Goniolenses
Direct goniolense is dome shaped lens
of high plus power which is placed over Table 1: Examples of direct goniolenses

the cornea to visualize the angle • Koeppe lens - +50 D lens (prototype
structures with the help of a hand-held direct goniolens) (Figure 3 a & b)
slit lamp or operating microscope,
while the patient lies in a supine • Richardon-Shaffer (Small Koeppe
lens for infants)

position. It is commonly used in • Swan-Jacob (Surgical goniolens)
(Figure 3 c & d)
surgical procedures or in bed ridden
patients or examination under
anaesthesia in children.

Figure 3 (a) and (b): Dome
shaped lens placed over eye for
direct gonioscopy- Koeppe’s
lens
(c) & (d): Intra-operative use of
direct gonioscope to see the
angle-Swan Jacob lens

ab

c bd

bb

Indirect goniolenses have a mirror on the inside of a contact lens to view the angle. The mirrors

reflect the light from angle to form an inverted angle image. Indirect goniolenses are of two types-

! Scleral type lenses: These lenses have a corneal contact well of a large size, which
fits onto the sclera, e.g. Goldmann 1 or 2 mirror lens. They may be used to perform
manipulation gonioscopy. Manipulation is used in gonioscopy to look over a steep
iris in angle closure disease or ‘over the hill view’. The patient is asked to look
towards the mirror which the observer is viewing to open the angle being viewed.
Since these lenses fit over the limbus, if too much pressure is applied, it leads to false
closure of angle in an otherwise open angle. The contact lens of these lenses has a
steeper curvature than the cornea; therefore a coupling fluid like methyl cellulose is
required to fill the space between the lens and cornea (Figure 4).

! Corneal type lenses: These lenses have small lens contact surface which rests well
within the limbus, over the cornea e.g. Zeiss/ Sussmann 4 Mirror lenses. They may be
used to perform indentation Gonioscopy. In angle closure disease, pressure is applied
using the contact lenses to displace the aqueous into the narrow angle to visualize
angle structures. Indentation can help differentiate between appositional and actual
synechial leading to angle closure. Indentation can also be used to open up the angle
and abort an acute angle closure attack in expert hands. The goniolens should be
applied gently over the cornea as too much pressure can falsely open a closed angle
and also result in corneal folds. The curvature of these goniolenses is similar to
cornea. Therefore, they don’t need coupling fluid (Figure 5).

Figure 4: Goldmann 2 mirror lens. Figure 5: Zeiss 4 mirror lens.

Table 2: Comparison of commonly used indirect goniolenses

Type of the lenses Goldmann Zeis Sussmann

Number of mirrors One/Two Three Four Four
Diameter of contact 12 mm 12 mm 9 mm 9 mm
Overall diameter 15 mm 18 mm 9 mm 9 mm
Mirror angulation 62° 59° 64° 64°
Mirror height 17 mm 12 mm 12 mm 12 mm
Radius of curvature 7.4 mm 7.4 mm 7.8 mm 7.8 mm
Coupling fluid Required Required Not required Not required
Dynamic gonioscopy Manipulation Manipulation Indentation Indentation

The mirror height in Goldmann 3 mirror is much lower than that in 2 or 1 mirror goniolenses.
This makes it highly un-suitable for manipulative gonioscopy and, hence, is not
recommended. Choosing a gonio lens may create confusion for practitioners because of
various available options. While Goldmann type 2 mirror lenses have a smaller learning
curve and are excellent for documentation of angle structures, one may find repeated use of
coupling fluid distressing over time especially when you have to visualize the fundus

after gonioscopy. Also, these lenses need rotation over the eye to view all angles,

hence any gonioscope with chipped edges may cause conjunctival trauma or haemorrhage.

The larger diameter may make it cumbersome to use in small eyes. The four mirror lenses

come with a handle or flange support. Although, gonioscopy with these lenses has a higher

learning curve, a smaller diameter and no requirement for coupling fluid make it more

widely useful. However, documentation of angle structures may be difficult

with 4 mirror lenses. Commonly used indirect goniolenses are compared in table 2.

Technique of indirect gonioscopy Indications for gonioscopy

How to apply goniolens? Diagnostic

After cleaning the gonioscope surface, - To identify open versus closed
informing the procedure to the patient and angle
instilling topical anesthetic, the patient is
positioned at the slit lamp in a room with - To assess for risk of angle closure
dim lighting (bright light can cause by assenting iris apposition to
pupillary constriction and open up an trabecular meshwork
‘occludable angle’).
- To grade angle closure and
distinguish between apposition
and synechiae

Scleral type lens - To identify angle pathologies like

The well of the goniolens is filled with abnormal angle pigmentation,
viscoelastic coupling fluid (2% HPMC). angle recession, foreign body,
Patient is directed to keep both eyes open developmental anomalies,
and the lower eyelid is retracted. The patient neovascularization of angle
is asked to look up. The gonioscope is - Post trabeculectomy patency of
placed at the lower limbus and gently fistula/ scleral opening

rotated over the cornea to avoid spillage of Therapeutic

coupling fluid. Patient is asked to look - Laser procedures like SLT/ALT
straight and may blink the other eye - Intraoperatively, to insert MIGS
normally, without squeezing. The thumb,
index and middle fingers hold the lens, like iStent or perform surgery
while the other two fingers may be placed like goniosynechiolysis

over the head of the patient.

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The patient is directed to look straight with eyes wide open and the gonioscope is placed

gently over the cornea keeping the mirrors in the 12, 3, 6 and 9 O'clock positions. Two

fingers hold the lens and others take support on the patient’s forehead or cheek. The lens is
gently held over the center of cornea to eliminate the air underneath the lens surface and
avoid formation of Descemet’s folds, which indicate excess pressure. If air bubbles form
underneath the lens surface, they can be easily removed by gently rocking the lens.

How to view the Angle?

Before application of goniolens, the slit beam height should be adjusted to 2-4 mm in height
and thin beam. When starting gonioscopy, the small and thin slit beam (to avoid miosis due to
bright light) should be projected at an angle of about 150 (theoretical best is 00 but that gives
lot of reflection) only on the superior mirror to view the inferior angle which is usually the
widest (due to angulation of lens) and maximally pigmented (due to gravity). Therefore, this
should be viewed first, followed by superior angle. The beam can be turned horizontal for
viewing the temporal and nasal angles. Examine each quadrant and note the findings. Once,
occludability of the angle has been assessed, illumination of slit lamp is increased, beam
widened and height increased to assess details of angle.

Normal angle structures visible on gonioscopy
It is important to know normal angle structures on gonioscopy to identify and differentiate
between angle closure and open angle. Gonioscopy helps in recognition of the following
landmarks (Figure 7).

In an adult with open angles, the following structures are visible, starting from anterior to
posterior – more open the angle, more structures visible) (Figure 6):

1. Schwalbe’s line
2. Non-pigmented trabecular meshwork
3. Pigmented trabecular meshwork
4. Scleral spur
5. Ciliary body band
6. Root of the iris

While corneal wedge denotes the Schwalbe’s line, visibility of scleral spur in all
quadrants denotes an open angle. If posterior pigmented trabecular meshwork is not visible in
>180 degree of angle, it denotes closed (Figure 7) or occludable angle. Presence of angle
closure warrants manipulation or indentation gonioscopy to look for angle opening.

Figure 6: Angle structures in a normal eye
Figure 7: A- Wide open angle with all angle
structures visible; red arrow showing
Schwalbe’s line and white arrow showing
trabecular meshwork ; B- Closed angle –blue
arrow shows blotchy pigments , no angle
structures visible

The corneal wedge-identification of the Schwalbe’s line

When a thin slit is projected into the angle of anterior chamber with an angle of 15-30 degree
between the eye piece and observer arm of the slit lamp, the reflection from inner and outer
cornea meet in a ‘U’ shaped manner at the termination of Descemet’s membrane which is the
beginning of Schwalbe’s line. This method is of great value in lightly pigmented angles and
in angles where there is difficulty in identification of normal landmarks or if there is pigment
deposition anterior to the Schwalbe’s line (Figure 8). However, one requires lots of focused
viewing and high magnifiction to be able to appreciate corneal wedge.

Schwalbe’s Line is the place where cornea Figure 8: Corneal wedge
fits into the sclera like a watch glass. In formation- red arrow
younger patients it is usually non-
pigmented. Fine pigment granules may Figure 9: Prominent
deposit with age, more so in inferior angle. Schwalbe’s line in
Abnormalities Axenfeld Rieger
syndrome- Posterior
! Posterior embryotoxon: prominent Embryoton –red arrow
anteriorly displaced Schwalbe’s line;
may be a normal variant or be Figure 10: (A)- fine
associated with the Axenfeld-Rieger pigment at Schwalbe’s
syndrome (Figure 9) line in normal angle-
white arrow; (B) Blotchy
• Blotchy pigments at Schwalbe’s Pigments at Schwalbe’s
line: while fine pigment dusting may line red arrow
be normal (Fig.10 A) but blotchy
pigments in a narrow angle is Figure 11: Heavy
suggestive of past closure which is Pigmentation of
an indication for YAG PI (Figure superior and inferior
10B). angle in Pigment
dispersion syndrome-
Trabecular Meshwork red arrows
It starts immediately after the Schwalbe’s
line. Being non-pigmented in young adults,
it gradually becomes pigmented with age,
especially in inferior angle. As most of the
aqueous flow occurs through the posterior
part, this gradually becomes pigmented, the
anterior part remaining non-pigmented. If
pigment is significant in the absence of
inflammation or trauma, especially if
superior pigmentation is equal/more than
the inferior quadrants, suspect:
a. Pigment dispersion syndrome (Figure 11)

b. Exfoliation syndrome

Schlemm’s canal

Schlemm’s canal lies deep to the pigmented trabecular meshwork and is not visible in most
individuals. Blood in Schlemm’s canal may be visible sometimes when gonioscope applies
too much pressure over the limbus raising the episcleral venous pressure. It should not be
confused with neovascularization of angle.

Scleral Spur

It is a white or light gray ridge anterior to the ciliary body band. It may be hidden in angle
closure or goniosynechiae.

Ciliary body band Figure 12: Abnormal widening of ciliary body band-
It is a dark gray or brown band of ciliary angle recession (black arrow); junction of normal
body before the iris root insertion. The width and recessed angle (white arrow)
of the band depends on the level of iris
insertion and tends to be wider in myopic
eyes and narrower in hypermetropic eyes.
The width of the band should be compared
between the two eyes before commenting on
any abnormality associated with a concussion
injury (e.g. angle recession, Figure 12).
Angle recession is best identified at junction
of normal and recessed region (white arrow).
Iris Processes

Iris processes are fine gray or brown lacy, finger-like extensions of the peripheral iris, which
follow the angle concavity, present in one-third of normal eyes (Figure 13). They are more
frequent in brown eyes and are not indicative of any disease process. They typically insert
into the scleral spur or posterior portion of the trabecular meshwork. They are often confused
with peripheral anterior synechiae (PAS). Dense iris processes may be seen in developmental
glaucoma.

Table 3: Differentiating characteristics of peripheral anterior synechiae and iris processes

Peripheral anterior synechiae (PAS) Iris Processes (IP)

• Broad base, usually tent-like • Fine, thread- like
• Bridge the angle recess • Follow angle recess
• Inhibit posterior movement of the • Do not interfere with iris

iris with indentation gonioscopy movement
• Drag normal radial iris vessels with • Vessels stay at original

them place
• Associated with anterior • May be associated with

pigmentation as a consequence of anterior insertion of iris
iris apposition in angle closure or esp. in developmental
pigment deposition in uveitis glaucoma

Figure 13: Iris processes- white Figure 14: Neovascularization of angle- white arrow shows
arrow vessel crossing the scleral spur and arborizing over trabecular
meshwork

Blood vessels in angle

In the normal angle, blood vessels may be visible blue eyes, related to the ciliary body or the
iris root. These normal blood vessels are typically broad and appear in short segments. They
do not extend anterior to the scleral spur. Vessels in neovascularization of the angle (NVA)
tend to be fine and may branch. They cross the scleral spur and arborize over trabecular
meshwork and follow no specific pattern. Common causes include central retinal vein
occlusion, proliferative diabetic retinopathy or any vaso-proliferative diseases (Figure 14).

Goniogram: Step by step documentation of gonioscopy findings

1. Posterior most structure visible in primary gaze with thin short slit beam
2. Posterior most structure on indentation or manipulation
3. Angle recess- degree
4. Iris configuration- concave, regular or steep
5. Any specific angle abnormality

a. Goniosynechiae
b. Pigmentation
c. Angle recession
d. Anterior insertion of iris
e. Iridodialysis/ cyclodialysis
6. Record any anomalies in the appropriate quadrant in a goniogram (Figure 15)

As alternative to writing grade of

angle, it is very practical to record the

most posterior structure visible during

gonioscopy (e.g. CB, PTM, ATM or

SL) and then mention the amount of

pigmentation, synechiae and any

adventitious structures like

neovascularisation, foreign body or

growth.

Figure 15: Goniogram for recording of angle configuration

Gonioscopy Grading Systems
Shaffer’s System describes the angle between trabecular meshwork and iris (Table 4).

Table 4: Shaffer system of gonioscopic grading

Grade Number Angle width Comments
4 35-45° Wide open – closure impossible
3 20-35° Wide open – closure impossible
2 20° Narrow – closure possible
1 ≤10° Extremely narrow – closure

Slit Slit probable
Narrowed to slit – closure probable

0 0° Closed

Angles > 20° are considered to be wide open
and incapable of closure. The angle is not
actually measured in degree; it is only a
rough estimation of the angle width (Figure
16).

Figure 16: Goniogram for recording of angle configuration

Spaeth system grades three aspects of angle anatomy:
1. Level of iris insertion.
2. Angular width of angle recess.
3. Iris configuration.
4. Angle pigmentation.
This system is very useful in research.

Follow-up of Gonioscopy
Annual review of gonioscopy should be done in PACS/PAC/PACG or POAG unless there is
an unexpected rise in IOP, wherein gonioscopy should be repeated early. POAG cases may
also develop angle closure over time with age, warranting a laser PI at a later stage.

Summary

In summary, gonioscopy is an indispensable tool in glaucoma diagnostics as well as
treatment. This is not only essential to differentiate between open and closed angles but also
to get a dynamic view of the angle of anterior chamber, see any abnormalities like pigment
related problems, neovascularization push from behind (like CB cysts) and many more.
Repeat gonioscopy is essential to know changes that may happen in the angle over a period of
time, especially due to increased thickening of the lens as a normal ageing process. Any
unexplained rise of IOP during follow up may also indicate some angle related cause, making

repeat gonioscopy essential. The importance of accurate documentation of findings cannot be
overemphasized. As far as therapeutic utility is concerned, it is required in all angle related
laser procedures, many (minimally invasive glaucoma surgeries) MIGS as well as childhood
glaucoma surgeries.

Steps of Sterilization of gonioscope

Gonioscopy is an invasive procedure and may lead to spread of infections through

infected gonioscopes. Hence, sterilization and disinfection of gonioscopes between uses is

must.

Steam autoclave or soaking in alcohol should not be done as it can damage the gonio.
Rinse
• Rinse immediately after use with clean cold water with mild

soap or detergent

Disinfection • After cleaning, the lens is disinfected

• Soaked in 2% glutaraldehyde for 20 minutes or

• 1% bleach solution (sodium hypochlorite) for 10 minutes

• The gonioscope can also be wiped for 10 seconds with a

sterile swab soaked in 70% isopropyl alcohol or cleaned with

1:1000 merthiolate solution

• It is then thoroughly rinsed with clean water and air dried

Sterilization (for • Ethyelene oxide exposure (ETO): by exposure at 56°C
use during surgery) (130°F) for one hour

• The sterilization of direct gonioscopes (Koeppe, Swan Jacob,

etc.) used during surgery can be done with ethylene oxide gas

sterilization

Suggested readings

1. Dada T, Sharma R, Sobti T. Gonioscopy: A Text and Atlas. Jaypee Brothers Medical

Publishers. 2013. New Delhi
2. Dada T, Sidhu T, Kumar A, Sharma A. Gonioscopy: A Video Assisted Skill Transfer

Approach. Jaypee Brothers Medical Publishers. 2016. New Delhi Dada T.
Gonioscopy DVD
3. Faschinger C, Hommer A. Gonioscopy. Springer Publishers, Austria 2012
4. Alward WLM, Longmuir RA. Colour Atlas of Gonioscopy. American Academy of
Ophthalmology 2008

About the author
Dr. Talvir Sidhu is assistant professor at Government Medical College, Patiala.
She has been a Senior Resident in glaucoma unit at AIIMS, New Delhi. She has
co-authored a book on gonioscopy and also published a video atlas on the same
subject. She has been associate editor for national guidelines published by AIOS
on Angle closure glaucoma and Primary Open angle glaucoma.