Gonioscopy

Gonioscopy is a procedure used in ophthalmology to determine whether the aqueous humor drains properly out of the eye. It is a common test for diagnosing glaucoma.

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General Description

Gonioscopy is an ophthalmologic test used to assess the condition of the drainage angle, the area located between the iris and the cornea through which the aqueous humor inside the eye drains. This procedure determines whether it is functioning properly or if there is any abnormality.

This test is primarily used to diagnose glaucoma and determine its type (open-angle or angle-closure), but it is also useful for detecting malformations, synechiae (adhesions between two epithelial layers, such as the iris and the cornea or the iris and the lens), or neovascularization that may lead to vision loss. Gonioscopy is also commonly used in the follow-up of otherwise healthy patients at risk of developing glaucoma.

When is it indicated?

Gonioscopy is mainly used to:

Diagnose glaucoma: the anterior segment of the eye (conjunctiva, iris, pupil, lens, and cornea) is examined.
Determine the type of glaucoma:
Open-angle glaucoma: the fluid does not drain properly.
Angle-closure glaucoma: the iris is too close to the drainage angle, causing blockage; this is a medical emergency.
Assess the condition of the eye and detect possible pigment deposits in the iridocorneal angle, synechiae, or the formation of blood vessels beneath the retina.
Identify structural abnormalities, whether congenital or acquired.

Patients with a family history of glaucoma, elevated intraocular pressure, or symptoms such as blurred vision or halos around lights are commonly referred for gonioscopy.

How is it performed?

This examination is based on the use of lenses that eliminate the light reflection occurring inside the eye, thereby allowing visualization of the iridocorneal angle.

There are two different techniques for performing gonioscopy, depending on the type of lens used:

Direct gonioscopy: a goniolens (typically a Koeppe lens) is used to modify the angle of light reflection and obtain a direct, panoramic view of the iridocorneal angle. To achieve this non-inverted image, a saline solution is used. The advantage of this procedure is that it allows comparison of both eyes, although it is a longer process in which the patient must lie down.
Indirect gonioscopy: this is the most commonly used technique. Gonioprisms with mirrors are used to obtain an inverted image of the area without changing orientation. It is a very simple technique that can be performed while the patient is seated at the slit lamp. Goldman or Zeiss lenses are typically used.

In both cases, anesthetic eye drops are applied to prevent discomfort. After placing the special lens, a beam of light is directed to reflect off the retina, and a microscope is used to examine the eye.

In some cases, dynamic gonioscopy is performed, in which pressure is applied with the lens to the eye to assess the opening of the iridocorneal angle or detect synechiae.

Risks

Gonioscopy is a safe procedure that does not damage the eyes. In rare cases, an allergic reaction to the anesthetic drops may occur.

What to expect from gonioscopy

Gonioscopy is an outpatient procedure that lasts just over five minutes, after which normal activities can be resumed immediately. In cases where the pupil is dilated for additional tests, blurred vision may persist for several hours.

For direct gonioscopy, the patient must lie down, whereas for indirect gonioscopy, the patient remains seated with the forehead and chin supported on the slit lamp.

Since anesthesia is used, the procedure is not painful. In some cases, a mild stinging sensation may be felt when the drops are applied.

The results, which are usually provided during the same visit, may indicate that the drainage angle is normal and unobstructed, or that it is obstructed, narrowed, or at risk of becoming so in the future.