7 Gonioscopy

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(midsized, used to view midperipheral fundus) and 73° (long, used to view peripheral fundus and ciliary body). The central wall has a diameter of 12 mm and radius of curvature of 7.38 mm. A newer modified version with 8.4 mm radius of curvature eliminates the need of using a coupling solution. The three mirrors also aid in retinal evaluation and laser therapy.

Zeiss lens (has under holder), or Posner (has a screw-in handle) four mirror has mirrors angulated at 64° and are amongst the most popular gonioscopy lenses. The Zeiss four mirror (Fig. 7.5) eliminates the need for rotation to evaluate the angle and it’s radius of curvature is 7.8 mm, closer to the corneal curvature, thereby eliminating the need for a viscous coupling agent. The diameter of the lens is 9.0 mm which aids in dynamic or compression gonioscopy, an important technique in evaluating narrow angles and angle-closure glaucomas.

Fig. 7.5: Zeiss four mirror lens

Protocol for a Routine Gonioscopy

1.Explain the procedure to the patient.

2.Reassure the patient and ensure cooperation.

3.Corneal surface is examined to rule out any contraindication for gonioscopy (abrasion, infection, significant corneal edema or opacity).

4.Adequate anesthesia is ensured using either 0.5% topical proparacaine or 4.0% lignocaine.

5.The patient and examiner should be in a comfortable posture with adequate support to examiner’s forearm and elbow to make sure of good control and minimal pressure over the eye throughout the procedure.

6.The lens is held in the examiner’s left hand for evaluating the right eye and vice versa.

7.The three-mirror gonioscope is filled with viscous solution and inserted as shown in Figure 7.6. The four-mirror is applied directly (Fig. 7.7).

Fig. 7.6: The inferior rim of three mirror gonioscope is inserted in the lower fornix with patient in upgaze as shown and swiftly tilted on to the cornea preventing loss of any coupling fluid

Fig. 7.7: The four mirror gonioscope is applied gently and directly on to the cornea. Fingers rested over cheek to ensure adequate support and prevent inadvertent pressure over the globe

8.The patient is asked to maintain a straight gaze once the lens is in situ.

9.Low, but adequate illumination, and small beams are focused on the mirror, with viewing and illumination maintained in the same axis. The illumination arm is moved paraxial when needed to evaluate the nasal and temporal recesses. Magnification and illumination can be increased when needed to evaluate finer details like new vessels and foreign bodies.

One quadrant can be evaluated at a time with the three mirror by sequential rotation while with the four mirror gonioscope all four quadrants can be evaluated without rotation and with minimum adjustments of the slit-lamp. Always remember the opposite quadrant (e.g. with mirror at 7 o’clock, the 1 o’clock angle) is being evaluated and the image is reversed but not crossed.

Other dynamic maneuvers like compression and over the hill evaluation are subsequently done. Over the hill maneuver involves asking the patient to look in the direction of the mirror; which in turn gives access to viewing angle recess over the convex iris. Compression techniques will be dealt with subsequently.

10.Disinfection of lenses is necessary prior and after every use because of the potential of transmitting infection. Lenses can be swiped dry with bacillocid (2% gluteraldehyde) or alternatively lenses can be rinsed with soap solution and water and allowed to dry.

Gonioscopic Anatomy and Interpretation

Repeated and routine normal gonioscopic studies are essential in adding to one’s experience in evaluating a pathological angle. A methodical evaluation of each structure either from iris plane

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Fig. 7.8: Gonioscopic landmarks of a normal angle: 1 Iris root, 2 Ciliary body band, 3 Scleral spur, 4 Trabecular meshwork, 5 Schwalbe’s line, 6 Schlemm’s canal, 7 Parallelopiped effect

to Schwalbe’s line (Fig. 7.8) or from iris plane to Schwalbe’s should curtail errors in interpretation.

To start with, from the peripheral iris plane one can follow upwards to the insertion of iris root. The contour of iris has several variations. The normal adult eye has a slightly convex contour. The same may be exaggerated in hyperopic eyes, where in the anterior segment it is crowded. A flat iris configuration is commonly associated with myopia and aphakia. A flat iris configuration with a peripheral convex roll or hump of iris that lies in close relation to the trabecular meshwork and can be seen in phakic normal eyes which often mimics a narrowangle and is referred to as plateau iris configuration. Contours could also be concave and are associated with high myopes and pigment dispersion syndrome. The insertion of iris root, may vary from a posterior, anterior or high insertions, thereby determining the visibility of the ciliary body band and the contour and depth of angle recess. The ciliary body band is composed of the anterior end of ciliary muscle

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and is seen as a slate gray or dark brown uniform band when insertion of iris root is posterior, anterior and high insertions preclude its view. An unusually wide ciliary body band may be seen in myopes and aphakes and may be confused with angle recession, but comparative gonioscopy and other signs of trauma help to distinguish between the normal and the pathological.

The next anterior transition is the scleral spur, the most prominent and most important landmark, identification of which is vital in terms of orientation of the angle. The scleral spur is the posterior lip of the scleral sulcus and is attached to the ciliary body band posteriorly and to the corneoscleral portion of trabecular meshwork anteriorly. It is visible as a glistening opaque white line between the ciliary body band and trabecular meshwork, however, identification at times may be difficult when the trabeculum is nonpigmented. The scleral spur may be obscured in the presence of dense pigmentation of angle structures like in posttraumatic or postsurgical situations. Iris processes, which are fine uveal strands arising from anterior iris surface and running upto the corneoscleral meshwork may also prevent a good view especially when they are prominent, as seen in congenital glaucomas. The spur is not visible in the presence of peripheral anterior synechiae or appositional angle-closure on routine gonioscopy.

The trabecular meshwork has a posterior functional, more pigmented portion and a less functional nonpigmented anterior portion. The corneoscleral part of the meshwork extends from the scleral spur to the Schwalbe’s line. The pigmentation of the meshwork varies with the kind of eyes, age and other pathological conditions. Brown eyes and adult eyes tend to have a deeper pigmentation compared to blue eyes and younger individuals. A nonpigmented trabecular meshwork may often present a tricky situation as far as accurate assessment is concerned, since its color and texture seems to

merge with the scleral spur. However, a careful evaluation reveals it to be a more translucent and less white structure. The parallelopiped effect is a useful adjunct that can be used in situations wherein the landmarks are indistinguishable. This effect causes a narrow-slit beam of light that is reflected from the anterior and posterior corneal surfaces to collapse at the Schwalbe’s line. Once this point is identified the other landmarks can be assessed based on the distance from the line.

The Schlemm’s canal is usually not visible, but can be seen through a less pigmented posterior trabeculum when reflux blood fills up either due to raised episcleral venous pressure, or rarely as a normal phenomenon. Excess pressure over the globe especially with a threemirror gonioscope can also cause artifactual filling up of the Schlemm’s canal with blood.

Schwalbe’s line as described before represents the peripheral termination of the Descemet’s membrane. Usually optically identified by the parallelopiped method, it also at times appears as a prominent white ridge known as posterior embryotoxon, a misnomer. This ridge is better appreciated when the patient looks in the direction of the mirror and is more prominent in the temporal quadrants. The line may occasionally be pigmented and is referred to as Sampaolesi line as seen in pseudoexfoliation and pigment dispersion syndrome.

Pediatric Eye

The pediatric eye has definite but subtle variations in its anatomy. The iris contour in a newborn is usually flat and its insertion is posterior to scleral spur with the anterior extension of ciliary body band visible. This contour does eventually become convex as the angle recess develops in 6-12 months. The trabecular meshwork is nonpigmented and appears thick and translucent. Congenital glaucomas present with

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Fig. 7.10: Gonio-photograph of a grade III Shaffer’s angle (corresponds to Spaeth—C30r). Landmarks are visible upto scleral spur with a mild iris convexity

Compression Gonioscopy

Compression or indentation gonioscopy is a simple and invaluable technique that one needs to know to assess narrow angles (Fig. 7.11) and chronic angle-closure situations. It helps distinguish appositional angle-closure from synechial angle-closure. The technique employs exerting external pressure over the cornea using the Zeiss, Posner or Sussman four mirror lenses; thereby forcing the lens iris diaphragm posteriorly and allowing to visualize the hidden angle recess (Fig. 7.12).

The technique involves a routine assessment of all quadrants, following which, if one subsequently decides the angle is narrow, each

Fig. 7.11: The photograph shows a narrow angle visible upto the Schwalbe’s line

Fig. 7.12: The same angle on compression widens to reveal landmarks upto scleral spur

quadrant is re-evaluated using a narrow slitbeam (to prevent miosis causing artifactual opening of the angle recess), pressure is applied directed towards the center of the eye. This results in deepening of the anterior chamber in the area of recess caused by bowing back of peripheral iris along with stretching of the limbal scleral ring and straightening of the angle recess; following this one can see structures that were not visible earlier, or confirm the presence of peripheral anterior synechiae. Corneal folds often distort the view but this can be minimized with appropriate technique in application of pressure. The physiological principles involved in compression gonioscopy have been depicted in Figure 7.13. Compression may not be effective when intraocular pressures are beyond 40 mm Hg as this limits the expansion of the limbal scleral ring.

Common Gonioscopic Findings and their Variations

Peripheral Anterior Synechia (PAS)

The peripheral anterior synechia is a pathological term referring to the adhesions of peripheral iris to the anterior angle structures, most often the functional trabecular meshwork, or rarely,

Fig. 7.13: Compression gonioscopy: a: The narrow angle appears closed on a routine gonioscopy, b: Compression fails to allow visibility of angle structures due to PAS, c: Compression widens the recess and allows a view of all structures in the absence of PAS

extending to the Schwalbe’s line. Typically seen associated with primary angle-closure glaucoma, uveitic and other secondary angle-closure glaucomas, PAS may often be confused with iris processes—which are normal fine lacy cords of uveal tissue extending from the peripheral iris to the trabecular meshwork. PAS on the other hand are broad adhesions commonly localized to quadrants with areas in between widening with indentation technique of gonioscopy. An angle that is closed 360° may often present a dilemma but one can follow the slit-beam from the posterior surface of the cornea which normally does not meet the beam on the iris directly in an angle that is open but instead lies alongside the other. A direct continuation of the beam without a break is suggestive of a closed-angle. Clinical correlation and experience will often help overcome this hurdle.

Blood Vessels

Normally all vessels in the angle are restricted to the ciliary body band and iris root and do not extend to the scleral spur or trabecular meshwork. Anomalous vessels are not rare, they, however, can readily be distinguished from neovascularization which are vessels usually

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arising from the peripheral iris surface and branching out in an arborizing and lacy pattern onto the corneoscleral portion of trabecular meshwork. Varying amounts of peripheral anterior synechiae may also be associated depending on the stage of disease process.

Pigmentation

The trabecular meshwork has a varying amount of pigmentation varying from 0 to 4, which is a subjective grading that correlates to none (0), faint (1), average (2), heavy (3), and very heavy

(4). Pigmentation increases with age under normal physiological conditions. Excessive pigmentation is usually pathological and is associated with pseudoexfoliation syndrome, pigment dispersion syndrome, traumatic and uveitic glaucomas.

Other Abnormal Findings

A variety of surprises may be hidden in the angle recess. Blood in Schlemm’s canal appears as a uniform linear reddish hue just anterior to pigmented trabecular meshwork and is associated with raised episcleral venous pressure. It can also be observed under normal conditions and as an artifact when excess external pressure is exerted during gonioscopy. Pseudoexfoliative material, microscopic hyphema and hypopyon can be visualized. Foreign bodies and emulsified silicone oil globules are among the other things that can be picked up by a careful gonioscopy.

Conclusion

In conclusion, the diagnostic basis of any glaucoma should be in correlation to the gonioscopic findings whenever possible. The management and prognosis of the disease depends on a complete diagnosis that includes

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a routine and periodic gonioscopic evaluation. Gonioscopy widens our scientific understanding of the disease process and guides us to manage the disease more effectively.

Bibliography

1.Epstein DL. Chandler and Grant’s Glaucoma (3rd edn). Philadelphia: Lea and Febiger, 1986.

2.Fellman RL, Spaeth GL, Starita RJ. Gonioscopy: Key to successful management of glaucoma. In Focal points Clinical Modules for Ophthalmologists, San Francisco, AAO 1984.

3.Kanski JJ, James AM, John FS. Glaucoma—A Colour Manual of Diagnosis and Treatment (2nd edn). London, Butterworth-Heinemann, 1996.

4.Kolker AE, Hetherington J Jr. Becker-Shaffer’s Diagnosis and Therapy of the Glaucomas (5th edn). St Louis, Mosby, 1985.

5.Neil TC, Diane CL. Atlas of Glaucoma. Martin Dunitz, 1998;39.

6.Palmberg P. Gonioscopy. In Ritch R, Shields MB, Krupin T (Eds). Glaucomas (2nd edn). St Louis, Mosby, 1996.

7.Shields MB. Aqueous humor dynamics. II. Techniques for evaluating. In: Textbook of Glaucoma (3rd edn). Baltimore, Williams and Wilkins, 1992.