Perimetry testing (visual field testing) for glaucoma

Examination Overview

Perimetry testing (visual field testing) measures all areas of a person's eyesight, including side, or peripheral, vision.

To do the test, the person sits looking inside a bowl-shaped instrument called a perimeter. While the person stares at the centre of the bowl, lights flash. The person presses a button each time he or she sees a flash. A computer records the location of each flash and whether the person pressed the button when the light flashed in that location.

At the end of the test, a printout shows if there are particular areas of the person's visual field where he or she did not see the flashes of light. These are areas of vision loss. Loss of peripheral vision is often an early sign of glaucoma.

Why It Is Done

Perimetry testing can help detect certain patterns of visual loss, indicating specific types of eye diseases. It is the single best test for diagnosing glaucoma. It is very useful in diagnosing early changes in vision caused by nerve damage from glaucoma.

Periodic perimetry testing can be used to see if treatment for glaucoma is preventing further vision loss.

Results

The amount of peripheral vision loss usually indicates the amount of optic nerve damage.

A person with open-angle glaucoma may have a specific pattern of vision loss. Vision loss first occurs farthest from the centre of the eye, usually on the nose side first. As the disease progresses, larger areas of vision loss are seen on perimetry testing. The area of the eye that provides the sharp, central vision (macula) you use for reading is usually damaged later in the disease, resulting in total blindness.

What To Think About

Testing the visual fields of a person using perimetry testing is an accurate way to detect vision loss caused by glaucoma. Perimetry testing provides a detailed representation of the person's visual fields. Baseline information can be compared with future test results. Detailed descriptions or drawings may also be used for later comparisons.

Perimetry testing often can be performed relatively quickly, but may take more than 45 minutes when both eyes are tested.

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Author:	Carrie Henley Robin Parks, MS	Last Updated: August 31, 2006
Medical Review:	Adam Husney, MD - Family Medicine Tom Bailey, MD - Family Medicine Carol L. Karp, MD - Ophthalmology
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