Gonioscopy--choosing the angle of attack: anterior eye and oculoplastics part 8 C-20105 O.
The anterior chamber angle is the angle between the anterior surface of the iris and the posterior surface of the cornea. It starts from Schwalbe's line anteriorly and runs to the ciliary body band adjacent to the iris insertion posteriorly (Figure 1).
Anteriorly, Schwalbe's line (representing the edge of Descemet's membrane) is seen as a white or opaque line, and below it is the trabecular meshwork, which runs to the scleral spur. Schwalbe's line acts also as a ridge anatomically and can be a point at which pigment released from the iris epithelium can be deposited, in some cases giving a pigmented line known as a Sampaolesi line (which was originally described in Exfoliation syndrome). The trabecular meshwork changes from the anterior non-pigmented component to the more pigmented posterior part, and so changes colour as you approach the white line of the scleral spur. Schlemm's canal is sometimes seen (especially if it contains blood) behind the posterior trabecular meshwork. The ciliary body band is located between the scleral spur and the iris insertion. Occasionally iris processes are seen running from the anterior surface of the iris to the scleral spur.
[FIGURE 1 OMITTED]
It Is Important to look for these structures when examining all eyes so that the examiner gets used to knowing what a normal angle looks like:
* Schwalbe's line
* Anterior trabecular meshwork
* Posterior trabecular meshwork
* Schlemm's canal
* Scleral spur
* Ciliary body band
* Iris insertion
* Iris processes
Every patient suspected of having glaucoma should have gonioscopy performed to determine the underlying mechanism causing the disease. The procedure allows glaucoma to be divided into two types: open and closed angle. It is also a useful technique for assessing the possibility of rubeotic/ neovascular glaucoma, which may develop in patients with central retinal vein occlusion (CRVO), proliferative diabetic retinopathy, and pigment dispersion/pseudoexfoliative glaucoma. It can also be used to assess the effects of injury to the eyes, looking for signs of angle recession, and congenital anomalies.
Light rays coming from the angle hit the cornea-air interface at an oblique angle and undergo total internal reflection, which prevents the angle from being seen. To overcome this, a goniolens (Figure 2, page 42) is used as it removes the cornea-air interface and (with the use of an angled mirror) allows the angle to be visualised. Gonioscopy can be performed directly or indirectly. The indirect technique is the commonest and is used with the slit lamp; the goniolens contains a mirror which allows examination of the opposite angle.
The main goniolenses used are the Goldmann lens and the Zeiss 4-mirror lens (alternatives are available). The Goldmann lens requires the use of a viscous coupling agent to fill the gap between the lens and the cornea, while (due to its different curvature) the Zeiss lens does not require this and instead relies on the tear film to perform this role. Both lenses have different advantages, with the Goldmann lens giving more stability and the Zeiss lens allowing a 360[degrees] view and the ability to perform indentation gonioscopy.
The patient and the examiner need to be relaxed for the procedure, and it is important to take your time and carefully examine the angle around 360[degrees]. After anaesthetising the cornea with topical anaesthetic (eg proxymetacaine 0.5%), the goniolens is placed on the cornea (with coupling fluid such as Geltears, if needed). To do this, ask the patient to keep both eyes open and look up. The lens can then be placed on the eye and the patient then asked to look straight ahead through the lens. The slit lamp beam should be slightly smaller than normal (to prevent light entering the pupil and constricting it) and the room lights dimmed--again to limit pupil constriction, which can artificially open the angle. In addition, try not to press too hard on the cornea, as this can cause indentation of the cornea which can artificially open the angle. Pressing too hard can also distort the peripheral cornea and obscure the view.
[FIGURE 2 OMITTED]
Depending on the shape of the iris (eg a convex iris) and configuration of the angle (eg a narrow angle), you may need to ask tOe patient to look towards the position oh the mirror to get the best view. Alternatively with a flat iris getting the patient to look away from the mirror will open the view. With the Goldmann lens you need to rotate the lens on the eye to view the whole angle (usually once into each quadrant), but with the Zeiss 4-mirror lens, the whole angle can be viewed from each of the four mirrors.
[FIGURE 3 OMITTED]
Indentation gonioscopy can also be performed with the 4-mirror lens and is a useful technique for assessing angle closure glaucoma. The angle is initially examined with minimal contact and with the patient looking in the direction oh the mirror, to assess the position of the iris insertion or contact between the trabecular meshwork and cornea. Pressure is then applied on the central cornea with the goniolens, which stretches the limbal scleral ring, causing the iris to flatten and the ciliary body and iris to rotate posteriorly, thus opening the angle. More angle structures may now/ be visible, which would confirm the presence of some appositional closure. Alternatively, if the iris remains stuck to the meshwork or cornea, this would indicate synechial closure or show the presence of peripheral anterior synechiae (PAS) where one area of iris remains attached and the iris either side moves bachwards.
What to look for
When examining the angle, you are essentially looking at how open it is, and for any pathological features. Each time you perform gonioscopy, the practitioner should go through the list of normal structures which should be seen from front to back and try to identify them. TMs will not only help you remember what to took for, but will also get you used to identifying differing levels of abnormality. Various grading systems have been designed to help document the gonioscopy findings and give a guide as to whether the angle is at risk of closure. The exact detail of the different systems can be found in various textbooks, but a summary is given in the following sections.
The Shaffer grading system
This is based on an estimate of the width of the angle in degrees and the angle structures which can be seen. Grade 0 (0[degrees]) is a closed angle with irido-corneal touch: and no visible structures. Grade 4 (35-45[degrees]) is a wide open angle with all structures to the ciliary body band being visible. Grades 1-3 lie in between these two grades and relate to increasing width and visibility of angle structures. The clinical relevance of the grading is that: Grades 3 and 4 are thought to be incapable of closing; Grade 2 is a possible risk of closure; and Grade 1 is a high risk for closure. With a closed angle (Grade 0), it is important to distinguish) between ap positional closure and synechial closure. To do this, indentation gonioscopy is used. With appositional closure, the angle will open and the iris will fall back away from the cornea, whereas with synechial closure, the iris remains stuck to the cornea and the angle will not open.
The Spaeth grading system
This is slightly more complex and allows for greater description of the various features. It takes into account the point of insertion of the iris, the curvature of the iris and the angle approach to the recess. The iris insertion is graded A-E, with A and B being above an d below Schwalbe's line respectively, C is at the Scleral Spur and D and E below this, with varying amounts of the ciliary body band viuble. The iris curvature is either normal (R for Regular), convex and bowed forward (S for Steep) or concave and bowed backwards (Q for Queer). The approach to the angle recess is graded in degrees, with 0[degrees] being closed and a gradually increasing degree as the angle approach is more open.
[FIGURE 4 OMITTED]
The Scheie grading system
This uses the visibility of the angle structures to grade the angle. Note that the numbering is the opposite of the Shaffer system, with Grade I being the widest open with a visible ciliary body and Grade IV being closed. Grade II indicates that the scleral spur is visible and Grade III indicates that only/ the anterior trabecular meshwork is visible.
What is it when it doesn't look normal?
The importance of examining lots of eyes is that you get used to seeing what is normal. This then helps you to identify abnormalities when they occur, even if you don't know what they are. Some of the key features which are abnormal are discussed in the following sections, along with their clinical relevance.
[FIGURE 5 OMITTED]
One of the most important features to look for is a narrow angle which is at risk of closure, or indeed a closed angle, with or without raised intraocular pressure (IOP) (Figure 3). This would correlate with Grades 2 and below on the Shaffer system, (Grades 3 and 4 on the Scheie system and a narrow approach, steep iris curvature and A and B insertions of the iris root on the Spneth system. Upon gonioscopy examination, little, if any, of the normal angle features can be seen and their is appears to be high up on the trabecular meshwork, or as far forward as the cornea with no angle features seen. If you have a Zeiss 4-mirror lens, perform indentation to see if the angle will open. Apposition of the iris to the trabecular meshwork and cornea, as seen in angle closure glaucoma, can lead to the formation of PAS, where the iris root sticks permanently to the trabecular meshwork. This can also be seen in chronic angle closure glaucoma. PAS can also be caused by trauma, inflammation and some rarer syndromes, such as Irido-corneal endothelial syndrome. It is important to distinguish PAS from iris processes which can occur in normal eyes. These cases need referral for consideration of periprieral iridotomy to try to reduce the risk of acute angle closure, and before any PAS can form.
Young people and those with light rides tend to have minimal pigmentation in the trabecular meshwork and it is seen in increasing amounts in older individuals and those with brown irides. It is graded from 0 (none) to 4 (very heavy). Various conditions cad cause pigment to be released from the iris pigment epithelium, which can be distributed id various places in the anterior segment and specifically the trabecular meshwork. The latter can be associated with raised IOP, eg in pigment dispersion syndrome and pigment dispersion glaucoma, the angle is usually wide open and the pigment tends to be more prominent in the posterior meshwork and Schwalbe's line is often pigmented, especially inferiorly (Figure 4). Other features such as Krukenbe'g spindles (pigmena cells on the corneal endothelium) can also be seen. In Pseudoexfoliation Syndrome, increased pigmentation of the trabecular meshwork can be seen, especially inferiorly. This is in addition to the exfoliation material which is seen in the anterior segment, and pigment which can also be seen on Schwalbe's line where it is known as a Sampaolesi line. Other more rare conditions such as trauma, uveitis and iris melanoma, can also lead to increased deposition of pigment in the trabecular meshwork. If these conditions are observed and the IOP is not too elevated, they can be referred for routine assessment. If they are associated with a very) high pressure (which can occur in some cases) then urgent referralis appropriate.
Normal vessels can be seen in the angle and are usually seen running radially at the edge of the iris. They are more often seen in people with light irides. These vessels do not tend to advance as far forward as the trabecular meshwork and any vessels in this area should raise concern. Neovasculnriation (the eormatioe of new blood vessels) is a major complication oh ischaemic conditions such as CRVO and proliferative diabetic retinopathy and the presence oh vessels on the iris and in the angle (Figure 5) can lead to the formation of neovascular membranes which can cover the trabecular meshwork and cause PAS formation. Subsequent neovascular glaucoma can be very difficult to treat. These new vessels are sometimes difficult to see, especially if high magnification is not used, and you may just see the membranes which contain the vessels. Friable new vessels in the angle can be seen in Fuch's heterochromic iridocyclitis, and there often bleed when the eye is opened, eg during surgery. Obviously, the presence of neovascularisation necessitates urgent referal to ophthalmology.
Following blunt trauma to the eye, several features can be seen on gonioscopy which can be associated with raised or low IOP. In angle recession, the angle appeard to be wide open and much deeper than normal. The iris appears to hip down peripherally and bare sclera may tie seen. If usually affects several adjacent clock hours anee is best Seen by comparing the gonioscopy features with rhe other eye. Secondary glaucoma with raised IOP can be astodated. A cyclodialysis cleft can also occur following trauma (which produces a direct channel between the suprachoroidal space and the anterior chamber) and can be a cabsu off a lowering of IOP. Clefts may be difficult to see and often require indentation for use off a viscoelastic at surgery) to make them visible, especially if they are small.
Gonioscopy is not difficult if you take your time and practice regularly. Select your lens of choice and become expert in its use. Learn the normal angle features and practice running through them each time you perform the procedure. Remember the types of abnormality to look for and conciously look for them each time you perform goinioscoey.
Ian Cunliffe qualified at Sheffield University Medical School and carried out his ophthalmology training in Sheffield and Cambridge, before spending a clinical Fellowship with associate professor ACB Molteno in New Zealand. His specialist area of interest is in glaucoma and his research interests are in visual field analysis and disc imaging. He is a consultant ophthalmologist at Midland Eye and the Heart of England NHS Foundation Trust. He is also a senior clinical tutor at the University of Birmingham.
See www.optometry.co.uk/clinical. Click on the article title and then on 'references' to download.
Module questions Course code: C-20105 O
PLEASE NOTE There is only one correct answer. All CET is now FREE. Enter online. Please complete online by midnight on December 28, 2012--you will be unable to submit exams after this date. Answers to the module will be published on www.oetometry.co.iik/cet/ exam-archive. CET points for these exams will be uploaded to Vantage on January 7, 2013. Find out when CET points will be uploaded to Vantage at www.optometry.co.uk/cet/vantage-dates
1. Which angle structure is the MOST anterior in the eye?
a) Scleral Spur
b) Posterior trabecular meshwork
c) Schlemm's canal
d) Schwalbe's line
2. Why does the Zeiss gonio lens not require a coupling fluid?
a) Total internal reflection is not relevant
b) It has a different curvature
c) It is easier to handle
d) The mirrors are placed at different angles
3. What is a closed angle graded as in the Shaffer grading system?
4. What is indentation gonioscopy useful for identifying?
b) Angle pigmentation
c) Appositional angle closure
d) Schwalbe's line
5. What is a Sampaolesi line?
a) Collection of pigment on the scleral spur
b) Collection of pigment on the posterior trabecular meshwork
c) Collection of pigment on the central corneal endothelium
d) Collection of pigment on Schwalbe's line
6. What can new vessels in the angle be a sign of?
b) Central Retinal Vein Occlusion
c) Primary Open Angle Glaucoma
d) Age Related Macular degeneration
Ian Cunliffe, MBChB, FRCS(Glasg), FRCOphth
Examination of the anterior chamber angle is an important part of diagnosing and managing several ocular conditions. The clinical technique of gonioscopy is important to learn. It is a difficult technique to master and requires a calm and systematic approach to performing it, if useful diagnostic information is to be gained. The examiner needs to be aware of the normal angle anatomy and to have an understanding of what abnormalities to look for. Having said that, once the technique is mastered, it will become a routine part of examination and not something to fear.
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|Date:||Nov 30, 2012|
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