Glaucoma: Nerve Fiber Analysis with the GDx

Introduction

"Glaucoma" is the term used for a family of eye diseases that are usually characterized by an elevated "intraocular pressure (IOP)" within the eye. When the pressure within the eye is high enough, it can damage the internal structures within the eye, causing vision loss.

Note: there are two types of glaucoma, one in which the fluid in the eye does not drain away efficiently, causing the pressure within the eye to increase gradually. The second type is caused when the drainage system of fluid from the eye becomes suddenly blocked. This second type, called "angle-closure glaucoma", causes blurred vision and severe pain. Angle-closure glaucoma is a vision-threatening emergency, and needs immediate treatment; this type of glaucoma is not being discussed here, however. The much more common, first type of glaucoma, called "primary open-angle glaucoma", is asymptomatic and is the subject of this article.

Increased IOP in primary open-angle glaucoma is almost always painless, and the vision loss usually occurs first in the outer edges of vision. Most people are not aware of any vision loss until the disease is quite advanced, which is one reason it is important to have regular eye examinations; if it is caught and treated early, the damage that occurs from glaucoma can usually be prevented.

Vision loss that occurs from increased IOP is permanent, so prevention of such loss is very important, especially when one or both parents had glaucoma. While the condition is not inherited in the same way that blue or brown eyes would be, there is definitely a genetic factor that causes glaucoma to run in families.

One place where increased pressure causes damage is the head of the optic nerve, where the retinal nerve fibers collect and make the turn to enter and form the optic nerve as it leaves the back of the eye. Another is to the nerve fiber layer itself, and that’s where the GDx instrument comes in, to help diagnose and prevent this damage.

Benefits of Early Detection

Nerve fiber analysis (NFA) is a test which allows for early detection and management of glaucoma, as well as other neurological disorders that affect the optic nerve. It measures the thickness of the retinal nerve fiber layer in the back of the eye, and provides information for evaluating the health of the nerves, often before any loss of central or peripheral vision is experienced.

The retinal nerve fiber layer is recognized as the first site of glaucoma damage, and can detect signs of the disease earlier than the more common tests, sometimes as much as six years before the characteristic visual field defects or vision loss occur.

Some of the benefits of this type of examination include:

1. Earlier detection of glaucomatous changes not possible with other tests

2. Monitoring progress and changes in previously diagnosed glaucoma patients

3. Enhanced management of glaucoma when combined with other testing, including IOP and testing of visual fields

4. Evaluation of neurological disorders affecting the optic nerve

What is the Test Like?

Examination by the GDx and evaluation of the nerve fiber layer usually takes less than five minutes. An image is acquired with a safe, scanning-type laser in less than a second, without touching the eye. The test collects information from over eleven thousand points on the retina to show an image of the optic nerve. No dilation of the pupils is needed, so there is no blur or other visual effects after the testing appointment.

Discussion

Glaucoma can affect people of all ages and races, although there are groups of people who are at greater risk. These include:

1. People over the age of 40

2. People with IOP which is elevated

3. People with a family history of glaucoma

4. Diabetics

5. People using long-term steroids

6. African-Canadians or African-Americans, especially those over age 35

7. People who are very myopic (nearsighted)

Your eyecare practitioner will recommend this testing if it is needed, and after testing, will evaluate the results and discuss the findings in terms of any further testing or treatment as indicated.

Glaucoma is one eye disease that can sneak up on its victims, because there are no early symptoms that might cause someone to suspect that they may have it. There is no pain, and the vision losses that happen early in the disease process are out in the periphery and are therefore not noticeable to most people.

Nerve fiber analysis is another testing strategy in the prevention of vision loss due to this insidious disease. This is certainly one area where advances in technology are proving themselves invaluable for early detection and treatment.