GONIOSCOPY

Gonioscopy is a test used by your ophthalmologist to determine if you have primary angle-closure glaucoma or if you are are at risk for developing it.

Gonioscopy usually is done if your ophthalmologist (eye doctor) thinks you should be checked for glaucoma, an eye disease that can cause blindness by damaging the optic nerve. If your doctor already has diagnosed you with glaucoma, gonioscopy can help her or him determine which type of glaucoma you have. This is important, since treatments for glaucoma are tailored to the type of glaucoma a person has.

Reasons for Performing Gonioscopy

• Examine the front of your eye (anterior chamber) to check for glaucoma.
• Visualize the area where fluid drains out of your eye (called the irideocorneal angle) to see of it is open or closed. This assists me in determining the type of glaucoma you have.
• Assess if there is any scarring or other damage to the drainage angle (iridocorneal angle).
• Check for the existence of lesions in the corner of your eye after trauma or the presence of blood vessel growth in the iridocorneal angle. Blood vessel growth is characteristic of neovascular glaucoma. It is seen in glaucoma patients with advanced diabetic retinopathy or occlusion of major blood vessels of the retina.
• Assess peripheral anterior synechiae (adhesion of the peripheral iris to the cornea).
• Examine anterior chamber for evidence of neoplastic activity (an abnormal proliferation of cells).
• Administer laser treatments to manage glaucoma
• Evaluate the eye for the presence of birth defects that may cause glaucoma.
• Observe in some cases the optic nerve and retina.

Great question! An ophthalmoscope is a hand-held instrument that is about the size of a small flashlight that I use during a standard examination to look into your eye. Specifically, it shines a concentrated beam of light that I use to look through the pupil of your eye to examine the health of the optic nerve, the retina, and the vitreous humor (fluid in the posterior part of the eye).

The anterior chamber in a normal eye forms an angle between 35 and 45 degrees. The reason that an ophthalmoscope cannot be used to examine this angle is because it is an instrument designed for direct observation (straight ahead). However, it is not possible to view the structures of the anterior chamber through direct observation. This is because the curvature of the cornea and scleral tissue (white of the eye) create an internal reflection that shines the concentrated light of the ophthalmoscope back into the instrument and makes visualization all but impossible.

To circumvent this problem, gonioscopy uses a special lens called a goniolens. This special optical lens has a concave surface that is placed against the cornea and eliminates it as a refracting surface. Under these conditions, all the structures that form the anterior chamber angle can be observed.

Goniolens resting lightly on the cornea.

There are four structures in the anterior chamber that are of particular interest to view in a gonioscopy exam: Schwalbe’s line, trabecular meshwork, scleral spur, and ciliary body.

Image of the anterior chamber by gonioscopy. SL Schwalbe's Line, TM Trabecular Meshwork, SS Scleral Spur, CBB Ciliary Body. Copyright 2010 - KAIIA LLC

These have a brown or gray and white color and are arranged in 360 degree bands in the iridocorneal angle. When the angle is not fully open, some of these structures cannot be observed. The fewer structures that are seen, the narrower the iridocorneal angle. This does not mean that they are missing entirely; rather it means that narrow irideocorneal angles do not permit the goniolens to visualize them.

If gonioscopy reveals that the four anterior chamber structures are visible, but intraocular pressure is elevated with accompanying evidence of optic nerve damage, then this is an indication that the patient has primary open-angle glaucoma. Conversely, if one or more of the four anterior chamber structures is not visible and intraocular pressure is elevated with some indication of optic nerve damage, this is evidence for primary angle-closure glaucoma.

No. Your ophthalmologist will apply eye drops before the exam that will numb your eye so that you will not feel the lens. Since the goniolens only lightly touches the cornea, there is no actual trauma to the eye. This means that you also will not experience any pain or discomfort when the exam is finished and the numbing effect of the eye drops wears off.

What should I do to prepare for a gonioscopic exam?

No special preparation is needed. If you wear contact lenses, remove them before the test. Wait for one hour after the test or until the medicine used to numb your eye wears off before reinserting them. Before the exam, ask your ophthalmologist if she or he plans to use medicine that will dilate the pupils of your eyes. If yes, it is a good idea to arrange for someone to drive you home after your visit.

How is a gonioscopy examination performed?

I perform gonioscopy in my office, as do most ophthalmologists. Depending on the type of equipment that your doctor uses, you either will sit in a chair or lie down for the exam. A biomicroscope with a slit lamp is used to look inside your eye. If you sit, you will rest your head on a chin rest and your forehead against a support bar and look straight ahead. I place the goniolens lightly on the front of your eye and a narrow beam of bright light is pointed into the lens. I then am able to visualize the iridocorneal angle and other structures in the anterior chamber of your eye.

As with any product there are different brands of goniolenses, but they all accomplish the same goal of visualizing the anterior chamber of the eye. The video below shows a typical gonioscopic exam. In this case, the ophthalmologist is using a Posner goniolens. I use a Goldmann goniolens, which is featured in the photo. But the important issue for patients is not the type of lens used for the exam, but rather if the procedure causes discomfort or pain. Notice in the video below that the patient does not jump or show any evidence of discomfort when the goniolens is lightly touched to her eye. Gonioscopy is a painless procedure that takes about 2 minutes to perform.

It is very important that you discuss these concerns with your ophthalmologist. She or he can lower your anxiety by explaining how severe your glaucoma is (patients do not always perceive vision loss) and can tell you what steps need to be taken to treat it. There is hope. A diagnosis of glaucoma does not automatically condemn you to blindness.

This question raises an important issue. The severity of a patient's glaucoma, including the likelihood that a person will develop vision loss or blindness, must be measured individually. The probability for vision loss increases if the diagnosis shows evidence of considerable damage to the optic nerve fibers or if intraocular pressure has not been adequately controlled with treatment or surgery.

The good news is that you do not have acute narrow-angle glaucoma, as this would have caused intense pain. Acute narrow-angle glaucoma is a medical emergency that requires immediate intervention to prevent permanent vision loss.

A close family of mine had an episode of acute narrow-angle glaucoma. My ophthalmologist recently told me that I have narrow angles, but no evidence of glaucoma. He recommended that I undergo a peripheral iridectomy anyway. Why would he prescribe surgery if I don't have glaucoma?

Your doctor has recommended this procedure as a precautionary measure to prevent acute narrow-angle glaucoma. Because acute narrow-angle glaucoma is a serious medical emergency, we often take steps to prevent it from occurring among those that are at high risk. It is likely that your doctor has determined that the narrowness of your angle is considerable. This narrowness may further increase with aging, which will put you at greater risk for developing acute narrow-angle glaucoma.

A peripheral iridectomy is a laser procedure that involves making a small hole in the iris. This allows fluid in the eye to pass into the anterior chamber (front part of her eye), which lowers intraocular pressure and has the effect of opening the angle to some extent. The procedure prevents an acute narrow-angle glaucoma from occurring. However, you still will need to have your intraocular pressure monitored regularly and you also should have periodic gonioscopic exams.

Return from Gonioscopy to Types of Glaucoma

Return from Gonioscopy to Eye Structure

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