Gonioscopy: Why Do Indentation?

Core Messages

›The Van Herick method of estimating peripheral anterior chamber depth does not replace gonioscopy. Plateau iris with angle-closure may be missed completely.

›Only indentation gonioscopy allows one to evaluate the dynamics of relative pupillary block, distinguish appositional from synechial angleclosure, and make an informed decision whether to perform an iridotomy.

›The diagnosis of “occludable angle” is a judgment call based on evaluation of the strength of relative pupillary block and the presence of appositional or synechial closure. Periodic gonioscopy is essential to evaluate progressive angle narrowing.

›Plateau iris is not an all-or-nothing phenomenon. Varying degrees of plateau are commonly found and not all plateau configurations are pathologic.

›Asian eyes have more angle-closure than African or Caucasian eyes, due to anterior iris insertion and general angle crowding. Creeping angle-closure is common and pupillary block may not be as important a factor.

›Anterior segment UBM or OCT exams are not substitutes for gonioscopy when making a decision about iridotomy. These exams cannot distinguish appositional from synechial closure.

14.1Which Patients Should have Gonioscopy?

Examination of the iridocorneal angle is an essential part of a complete ophthalmic examination, but a busy practitioner will not put a goniolens on every new patient. So, which patients should be examined? Glaucoma-related reasons to do gonioscopy include: identification of eyes at risk for angle-closure; evaluation of the extent of known angle-closure evaluation of the angle of any eye at risk for a secondary glaucoma: pseudoexfoliation, pigmentary dispersion, uveitis, past history of contusion, retinal vein occlusion, diabetes, etc.; treatment of the angle by laser: trabeculoplasty, iridoplasty, goniopuncture; verification of patency of a trabeculectomy, and, last but not least, learning the anatomy of the normal angle. Gonioscopy should be done routinely in cooperative patients when time permits to learn the variations in normal angles (Figs. 14.1 and 14.2). If a lens is only put

Fig. 14.2  Another normal angle open to the ciliary body band with little trabecular pigmentation

on eyes with narrow angles it will be more difficult to distinguish normal from the pathologic.

Summary for the Clinician

››Gonioscopy should be performed

––To learn the anatomy of the normal angle.

––On eyes at risk for angle-closure.

––To evaluate the extent of known angleclosure.

––To evaluate angles in eyes at risk for secondary glaucoma.

––On eyes where laser or incisional angle surgery is contemplated.

––To internally evaluate a trabeculectomy or tube shunt.

14.2  Of What Use is the Van Herick Angle Examination?

The Van Herick test provides a very rapid, non contact evaluation of peripheral angle opening [11]. A narrow slit beam is directed at the peripheral cornea just adjacent to the limbus at a 60° angle and the distance between the endothelium and iris surface is estimated. If the anterior iris surface is very close to the endothelium (closer than ¼ corneal thickness) the angle approach is considered narrow. This examination is very useful to identify

wide open angles with deep anterior chambers. A major problem with the Van Herick test is that a plateau iris configuration can be entirely missed. The angle approach may appear open despite the presence of abnormal pathology closer to the iris root. On the other hand, a fluffy, thick peripheral iris can appear as a narrow nasal or temporal angle on the Van Herick test, but gonioscopy can exhibit an open angle with no risk of angleclosure. The Van Herick exam is done as a first step, but anytime there is the slightest doubt as to depth of the peripheral chamber, one must put on a goniolens.

Summary for the Clinician

››Van Herick’s test evaluates the depth of the peripheral anterior chamber near the limbus.

››It is not a substitute for gonioscopy.

14.3  What Lens Should be Used for Gonioscopy?

Standard single or triple mirror Goldmann type lenses are insufficient to evaluate the iridocorneal angle since they provide a static picture of the angle, which will not properly represent angle dynamics. Peripheral iris configuration, the amount of relative pupillary block, and the antero-posterior position of the iris-lens diaphragm vary with accommodation and pupillary diameter. Use of indentation gonioscopy is indispensable to evaluate relative pupillary block and to distinguish between appositional (reversible) and synechial (permanent) angle closure­.

The classic Goldmann triple mirror lens has a contact surface diameter equivalent to that of the cornea with a small radius of curvature requiring viscous coupling fluid between it and the eye. It is impossible to indent the cornea with this lens since force is transmitted to the limbus. Instead, what is desired is for force to be transmitted across the cornea so that aqueous humor is pushed from the center of the anterior chamber into the angle. Indentation gonioscopy lenses have corneal contact surfaces 8 mm in diameter close to the corneal curvature with rounded edges. See Fig. 14.3. Available lens models for indentation gonioscopy include the Zeiss glass fourmirror lens on an Unger fork, Posner four-mirror lens on fixed handle, and Sussman lens without a handle.

Fig. 14.3  Standard triple mirror lens with large contact surface and sharp rim compared to an indentation goniolens with smaller contact surface and rounded edges

Summary for the Clinician

››Goldmann type lenses provide a clear view of the angle but do not allow for dynamic gonioscopy and thereby, important features of the angle can be missed.

››The Zeiss, Posner, and Sussman lens have a smaller diameter corneal contact surface which allows indentation gonioscopy to be performed.

››Indentation gonioscopy is critical as it allow one to distinguish between permanent and reversible angle-closure.

14.4  How Do I Perform Indentation

Gonioscopy?

Fig. 14.4  Indenting the superior mirror moves aqueous humor across the anterior chamber forcing the peripheral iris of the inferior angle backwards. What was simply a closed angle on static gonioscopy can now correctly be identified as closed by apposition only

One begins with a drop of topical anaesthetic. If the central corneal thickness is to be measured it is best done before gonioscopy. In a dimly lit or dark room with a fine slit beam outside of the pupil to prevent miosis, the lens is placed on the eye so that the mirrors sit in either a square or diamond configuration. No viscous fluid is required with the lenses for indentation gonioscopy. The hand holding the lens can be steadied by one finger touching the patient’s cheek. Since all four mirrors have the same angle of inclination, there is no need to rotate the lens to see all quadrants. A static view is obtained first with the lens gently placed on the cornea. Then one begins to indent.

Instead of pushing the entire lens uniformly into the cornea, I have found it best to push or “heel in” only the mirror in which you are looking (Figs. 14.4 and 14.5). Aqueous humor is pushed across the anterior chamber

Fig. 14.5  Indentation of the inferior mirror demonstrates irreversible synechial closure of the superior angle

applying force to the peripheral iris which will move posteriorly. A very slight movement of the lens towards the angle you are examining is also required while heeling in the mirror. You can release and reapply pressure to judge the importance of relative pupillary block (Figs. 14.6 and 14.7) or to see if appositional or synechial

closure is present. The eye diagrammed in Figs. 14.4 and 14.5 would show a completely closed angle with static gonioscopy. Indentation revealed that the inferior angle in Fig. 14.4 could be opened, meaning there was appositional closure only. In Fig. 14.5, the superior angle remains closed by peripheral anterior synechiae (PAS). Figure 14.8a (static view) and Fig. 14.8b (during indentation) show an angle closed by apposition only. There is a definite learning curve to become comfortable with the indentation lens, but once the technique is mastered, this will most likely become the only lens you use for diagnostic gonioscopy.

Fig. 14.7  Indentation gonioscopy can flatten out the peripheral iris. The strength of the relative block can be estimated by answering the question: how much pressure on the cornea is necessary with each indentation to move the iris backwards?

Fig. 14.8  (a) Static view of a closed angle. No angle elements are visible. (b) With indentation the angle can be opened to the scleral spur. Prolonged iridotrabecular contact can leave traces of adherent pigment seen here across the trabecular meshwork