An appreciation of gonioscopy

Many ophthalmologists undervalue this key diagnostic test. Why they’re wrong.

By Andrew Rabinowitz, MD

About the Author
	Andrew Rabinowitz, MD, is a glaucoma specialist at Barnet Dulaney Perkins Eye Centers, a multi-location practice based in Phoenix. His e-mail is andrewrabinowitz@aol.com. Disclosure: Dr. Rabinowitz has no relevant financial interest in any product mentioned in connection with this article.

Just as the stethoscope is becoming a relic amongst cardiologists, the gonio lens is being relegated to the storage drawer in ophthalmology practices across the country.

Ophthalmologists are beginning to embrace anterior segment ultrasound and anterior chamber OCT imaging in lieu of the tried and true standard of gonioscopy. I would argue that, although anterior segment imaging systems are all the rage and will likely yield informative data as we apply these technologies more liberally, they do not replace gonioscopy.

Anterior segment imaging systems may provide ancillary information about the depth of the filtration angle. I have not, however, seen an imaging system that tells me more about the filtration angle than the standard gonio lens.

COURTESY ANDREW RABINOWITZ

I use gentle pressure to perform dynamic gonioscopy with a four-mirrored lens on a straight handle. The straight handle allows for the necessary manipulation of the lens to evaluate all the filtration angle.

Here, I will explain the important role of gonioscopy in glaucoma diagnosis and why we should more highly value this test.

A diminished role for gonioscopy

As a glaucoma specialist who closely observes trends in my specialty, I can report that gonioscopy is today one of the least commonly performed components of the ophthalmic exam. However, its frequency of use does not reflect its importance in the diagnosis and treatment of glaucoma.

I believe several reasons explain the fact that gonioscopy is not performed with great frequency anymore. Examination of the filtration angle can be technically challenging and identification of the angle structures can be difficult. Repetition can help the examiner overcome these challenges. Study of the trabecular mesh-work produces a broad array of presentations with significant overlap in their appearances. The angle can vary in depth as well as degree of pigmentation. The width of the trabecular meshwork, scleral spur and ciliary body band (CBB) can vary as well.

Why perform gonioscopy?

The classic reason for performing gonioscopy is to determine if a patient has potentially occludable angles. If a patient does have occludable angles, the diagnosing ophthalmologist should educate the patient regarding the risks of angle closure and offer options for alleviating this risk, or refer the patient to a colleague who can perform the appropriate laser or surgical procedure.

The information the gonioscopy exam garners is not limited to the presence or absence of occludability. Other pertinent gonioscopic findings include the degree of angle pigmentation, as well as the homogeneity or heterogeneity of the meshwork width, the width of the scleral spur, and status of a CBB. Examining and describing these angle structures is key to identifying the glaucoma mechanism in a particular patient.

COURTESY ANDREW RABINOWITZ

I place the gonio lens on the eye, the tear film coupling the lens to the eye.

GONIOSCOPY FOR A RANGE OF CONDITIONS

Pigmentary glaucoma

Aside from the narrow-angle glaucomas, the next most common glaucomas in which angle information is pertinent are the pigmentary and pseudoexfoliative glaucomas. In both pigmentary and pseudoexfoliative glaucoma, we see heavy angle pigmentation. One can appreciate this pigmentation both by virtue of the darkened Sampaolesi’s line as well as darkening of the trabecular meshwork itself.

In the case of pigment dispersion syndrome or pigmentary glaucoma, the darkened meshwork pigmentation is accompanied by pigment on the corneal endothelium as well as iris transillumination defects. Pigmentary glaucoma is usually a bilateral disease with an asymmetrical presentation. Pigment dispersion syndrome refers to the condition in which the liberated pigment serves to obstruct the trabecular meshwork. If the obstructed meshwork leads to a significantly elevated IOP of long enough duration, then optic nerve damage will ensue. This nerve damage is considered to represent pigmentary glaucoma.

Pseudoexfoliative glaucoma

Gonioscopy is also a vital tool in the diagnosis and management of pseudoexfoliative glaucoma. Similar to pigmentary glaucoma, the gonioscopic examination in pseudoexfoliative glaucoma will reveal heavy mesh-work pigmentation. Unlike pigmentary glaucoma, pseudoexfoliative glaucoma usually does not reveal pigmentation on the corneal endothelium.

Additionally, iris transillumination does not usually accompany pseudoexfoliative glaucoma, which can present either unilaterally or, occasionally, bilaterally. In the unilateral presentation, the eye with pseudoexfoliative glaucoma will have dramatically heavier angle pigmentation than the fellow eye.

Traumatic angle-recession glaucoma

Another type of glaucoma for which gonioscopy is necessary for a proper diagnosis is traumatic, angle-recession glaucoma. Unlike narrow-angle glaucoma, traumatic angle-recession glaucoma is notable for an unusually deepened angle. The scleral spur can have a wider-than-usual appearance. Findings in traumatic angle recession are usually unilateral, but both eyes require examination to make a proper comparison.

Tumorous eyes

Intraocular tumors, including those of the angle, iris, cornea and uvea, will often reveal unusually darkened angle pigmentation. These changes in pigmentation will be unilateral in most cases. Unlike pigmentary or pseudoexfoliative glaucoma in which pigmentation is heaviest inferiorly due to effects of gravity, the heaviest pigmentation in tumorous eyes appears in the quadrant closest to the neoplasm.

Neovascularization

In patients suspected of having neovascularization of the iris or angle, such as that with central retinal vein occlusion or proliferative diabetic retinopathy, gonioscopy is vital to determine if abnormal blood vessels have proliferated into the filtration angle. If so, one of the current antiangiogenic agents and possibly pan-retinal photocoagulation, if indicated, are required to treat the underlying neovascularization.

It is vital to assess for the presence of neovascularization in the angle because failure to do so can lead to sub-optimal treatment of the angiogenic process. The consequence of neovascularization of the iris or angle, or both, is the formation of synechial adhesions of the iris over the trabecular meshwork, leading to permanent obstruction of aqueous outflow. Patients with neovascular glaucoma often go on to require aqueous shunt surgery to provide adequate aqueous outflow. Thus, a thorough gonioscopic exam is critical in the evaluation of neovascular diseases.

GONIOSCOPY 101: HOW I PERFORM THE TEST

Initial evaluation

To perform dynamic gonioscopy, I use a four-mirrored lens coupled with the patient’s tear film. I prefer a Posner- or Sussman-style lens.

When I apply the lens, my initial evaluation is of the inferior angle. The inferior angle will likely be the deepest. If the inferior angle is occludable, it is nearly certain that the angles will be occludable in all other quadrants, which are naturally shallower. This is because gravity forces aqueous humor into the inferior angle, providing the greatest separation between the cornea and the iris.

While examining the inferior angle in the superior mirror, I try to put little to no pressure on the lens, thus providing the most physiological view of the angle. I then use gentle pressure to try to deepen the angle. This allows me to differentiate appositional closure from synechial closure. In the presence of synechial closure, pressure will not successfully deepen the angle.

Superior and horizontal angles

If I cannot appreciate the scleral spur when examining the inferior angle without pressure, I would deem the angle to be potentially occludable. Once I have assessed the inferior angle without pressure — and then with pressure — I move to the superior angle followed by the horizontal angles.

The angle pigmentation usually falls off dramatically as you move away from the inferior angle, again due to effects of gravity on the pigment. The inferior angle will usually show the heaviest trabecular pigmentation. One exception to this can be seen in neoplastic diseases where the heaviest pigment usually appears in the vicinity of the tumor, regardless of its anatomic position.

As part of the initial examination

I suggest performing gonioscopy on all patients at the time of their initial exam regardless of whether they are phakic, pseudophakic or aphakic. Even in pseudophakic patients, understanding the angle anatomy in a given individual can help gain a better understanding of the mechanism of glaucoma in a particular patient.

Finally, with a flurry of new surgeries, such as the iStent (Glaukos, Laguna Hills, Calif.), which place filtration devices into the angle at the time of cataract surgery, it will become vital to master the techniques of gonioscopy to both place and track the integrity of these shunting devices in the years to come. OM