Fig. 7-8  Gonioscopic evaluation of the angle necessitates careful evaluation of the confluence of the slit-lamp beams as they course down the cornea and across the iris to meet in the angle. If the true depth of the angle is being visualized, then the beam will meet in the angle as illustrated here. If one is not seeing fully into the angle where the iris and cornea come together, these beams will be slightly misaligned from one other.

With a Koeppe lens, the patient’s nose sometimes prevents adequate visualization of the upper temporal angle. Gonioscopy is accomplished by having the patient look up and temporally. To avoid intrusion of bubbles, the lens should be held by an assistant. With any of the indirect gonioscopic lenses it is difficult for the examiner to retain binocularity when examining the horizontal areas of the angle.Accurate centering of the mirror or prism is helpful. When high IOP produces corneal epithelium edema, the use of multiple topical glaucoma drugs, or even an oral hyperosmotic agent, can improve visualization by lowering pressure. Anhydrous glycerol drops administered topically also will dehydrate the corneal epithelium. Rarely, as for goniotomy, it is necessary to remove the hazy edematous corneal epithelium by curettage.

Endothelial dystrophy, or even mild cornea guttata, decreases the clarity of the angle image. Focusing on the cornea during gonioscopy provides an oblique view of the defective endothelium, which has a pebbled, shagreen appearance against the white background of the scleral tissue. The diagnosis of cornea guttata is often easier with this method than with direct slit-lamp microscopy.

Clinical usefulness of gonioscopy

Aid in Diagnosis of Type of Glaucoma

Using gonioscopy alone, the examiner can determine which eyes are in critical danger of angle closure and which are completely safe from closure. This finding forms the basis for classifying eyes into angle-closure glaucoma and open-angle glaucoma types. It is also important to remember that an eye’s gonioscopic status is not static and determined in perpetuity by a single baseline

­examination. Long-term dynamic factors such as lens changes, medication effects, aging, and disease processes make periodic gonioscopy an important feature of appropriate glaucoma management.

In open-angle glaucoma, gonioscopy may reveal inflammatory precipitates31 or a fibrovascular membrane, or it may reveal a tumor that is covering or invading the trabecular meshwork.An early sign of impending neovascular glaucoma may be a network of blood vessels growing anteriorly on the trabecular wall. Usually, a similar network appears around the pupil at a slightly earlier stage of the disease, but even the lightest pressure of an indirect goniolens, such as the Zeiss, may blanch small neovascular tufts and render them invisible.32 Blood vessels seen crossing the scleral spur are considered a definitive sign of pathology.33 These new vessels can extend as high as Schwalbe’s line.When the accompanying fibrous tissue shrinks, peripheral anterior synechiae and ectropion uveae are produced. New vessels branch and wander irregularly over the surface of the iris; this is in contradistinction to normal radial vessels, which are straight, uniform, and usually covered by iris stroma. Portions of the major circle of the iris normally are seen in the angle posterior to the spur as thickened vessel loops rising up from the stroma in a ‘sea serpent’ appearance. Normal vertical vessels are seen intermittently within the depths of the posterior angle wall. All of these differ from the superficial, arborizing small vessels that are typical of neovascularization.

With the patient lying supine for Koeppe gonioscopy, mild iridodonesis can be seen in some normal eyes, particularly if they are myopic (as with pigment dispersion syndrome). Iridodonesis is particularly prominent in eyes with aphakia, a dislocated lens, pseudophakia, or pseudoexfoliation. A marked trabecular pigment band is characteristic of both pigment dispersion and the pseudoexfoliative syndrome.The exfoliated material often is well visualized as poised on the edge of the pupil, against the contrasting dark pigment of the iris pigment layer.

Easily overlooked causes of secondary glaucoma can be revealed by careful inspection at the time of gonioscopy: finding a foreign body in an angle; seeing holes in the peripheral iris caused by the passage of an intraocular foreign body; observing a traumatic angle recession; appreciating precipitates on the trabecular surface; or recognizing blood in Schlemm’s canal, suggestive of increased venous pressure or inflammation. If no obstruction at the trabecular meshwork can be seen, the block to outflow must be beyond the trabecular surface – and by default the diagnosis is open-angle disease.

Evaluation of Symptoms

When a patient complains of halos around lights, this symptom should suggest episodes of angle-closure glaucoma if the angles are found to be critically narrowed. If the angles are wide open, however, the risk of sudden, catastrophic tension elevation by angle closure is virtually non-existent, and the history of halos warrants another explanation. Appreciation of the signs of pigment dispersion syndrome, such as Krukenberg’s spindle, iris transillumination defects, and heavily pigmented trabecular meshwork, can explain sudden episodes of visual disturbance from ‘pigment storms’ following intense activity.34,35

Use of Drugs

If an angle is found to be wide open, it is safe to use strong miotics, mydriatics, or sympathomimetics freely. Such use might

cause the angle to close completely in eyes with narrow angles, precipitating an acute rise of IOP. If miotics become necessary for the management of glaucoma in an eye with a narrow angle, the angle should be re-evaluated after therapy has begun. Occasionally, miotics narrow the angle further as a result of forward lens shift and enhanced pupillary block. Therefore, in narrow-angled eyes, any change in therapy should be monitored by periodic and frequent gonioscopy.

Particularly in eyes with narrow angles, the decision to operate may rest largely on the gonioscopic findings. If IOP is elevated at a time when the angle is definitely open but narrow, iridotomy will not cure the glaucoma.

When planning intraocular surgery, the surgeon should be sure to note the position of peripheral anterior synechiae and large blood vessels.Avoiding such areas may prevent serious complications.

Postoperative Examinations

The success of iridotomy in opening an angle and of cyclodialysis in producing a suprachoroidal cleft (Fig. 7A-14) can be evaluated promptly. After filtering procedures, the surgical stoma can be seen gonioscopically. If filtration is impaired, the appreciation of a patent ostium will direct attempts to restore the bleb by addressing the episcleral surface – suture lysis, bleb needling, or resections of scar tissue beneath the conjunctiva. If the ostium is occluded by the iris or adhesions, it may be re-opened using laser.

Conditions Other Than Glaucoma

The diagnosis of peripheral tumors or cysts often can be made by gonioscopy. Operability can be determined by an accurate view of the extent to which the iris and ciliary body are involved, supplemented by anterior segment imaging with UBM. Foreign bodies in the angle and holes in the peripheral iris from penetrating foreign bodies may be discovered. Inflammatory and traumatic conditions, such as keratic precipitates covering the meshwork and iridodialysis, can be visually evaluated.

When a portion of the cornea is hazy, it may be possible by gonioscopy to look through a clear portion of cornea to see the reason for the haze.Tears in Descemet’s membrane, epithelial downgrowth, and areas of vitreous adhesions can be diagnosed in this way.

Gonioscopic examples are given in the ‘Color illustrations’ at the end of this chapter (Figs 7-A3 through 7-A16).

Summary of Important Gonioscopic Techniques

In clinical practice, unusual situations can arise. The following special techniques can be used to arrive at a correct diagnosis:

1.  Flashlight test (see Fig. 7-3). In the absence of slit-lamp or gonioscopic equipment, the shallow chamber of the narrow-angled eye can be identified by holding a small-beam light source parallel to the plane of the iris at the limbus, shining across the eye. With a potentially occludable angle, the lens diaphragm can be seen to bow forward and produce a shadow on the side opposite the light.

2.  Slit lamp (see Fig. 7-2). A slit-lamp estimation of the angle without a goniolens (van Herick method) is helpful in screening

A

B

Fig. 7-9  Retroillumination of angle structures. Light directed from point A strikes the cornea anterior to the angle and is internally reflected within the cornea and sclera. The pigment in the trabecular meshwork and ciliary body prevent the light from entering the angle. The scleral spur (B) lights up brightly. (From Hoskins HD Jr: Interpretive gonioscopy in glaucoma, Invest Ophthalmol 11:97, 1972.)

patients. It is particularly useful when contact lens visualization of the angle is poor through a cloudy cornea.Training in the use of a commercially available reticule for the viewing lens of the slit lamp can allow for consistent, quantitative assessment of angle depth – of great value in population surveys.26

3.  Simultaneous bilateral gonioscopy. Comparison of corresponding areas of the angles of the two eyes is facilitated by placing a Koeppe contact lens on each eye simultaneously. Thus the examiner can go back and forth comparing corresponding sectors of each angle. Subtle differences, such as unusual iris processes, angle anomalies, peripheral anterior synechiae, and especially areas of angle recession, often are identified best by this comparison.

4.  Gonioscopy of the fellow eye. When conditions prevent accurate gonioscopy of the affected eye, examination of the fellow eye may aid in the diagnosis.

5.  Indentation (compression) gonioscopy (see Fig. 6-9). Indentation of the central cornea with a Zeiss lens widens the peripheral angle. This is useful in a narrow-angled eye to distinguish between areas of iris apposition and permanent peripheral anterior synechiae. Also, it helps the examiner estimate the width of a narrow angle because additional angle structures are exposed to viewing.

6.  Management of corneal edema. Epithelial edema can be reduced by lowering the IOP, particularly by using hyperosmotic agents intravenously or orally, in conjunction with a variety of topical medications. Mechanical removal of the edematous epithelium is effective and is of particular value in infantile glaucoma.

7.  Retroillumination of the angle structures. By using scleral scatter (Fig. 7-9), angle structures sometimes can be seen during gonioscopy and identified more accurately than with direct illumination.

8.  Endothelial mosaic. Gonioscopic visualization of the endothelium may show subtle degenerative changes.

9.  Pseudoexfoliative syndrome. Exfoliated material is diagnosed best in the undilated eye by seeing the dandruff-like deposits on the pigment epithelium beneath the edge of the pupil.