A perimetry test (visual field test) measures all areas of your eyesight, including your side, or peripheral, vision.

To do the test, you sit and look inside a bowl-shaped instrument called a perimeter. While you stare at the center of the bowl, lights flash. You press a button each time you see a flash. A computer records the spot of each flash and if you pressed the button when the light flashed in that spot.

At the end of the test, a printout shows if there are areas of your vision where you 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

A perimetry test can help find certain patterns of vision loss. This may mean a certain type of eye disease is present. It is the single best check for glaucoma. It is very useful in finding early changes in vision caused by nerve damage from glaucoma.

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

Results

The amount of peripheral vision loss is linked to the amount of optic nerve damage.

A person with open-angle glaucoma may have a certain pattern of vision loss. Vision loss first occurs farthest from the center of the eye, usually on the nose side first. As the disease gets worse, larger areas of vision loss are seen on a perimetry test. The area of the eye that gives you the sharp, central vision (macula) you use for reading is usually damaged later in the disease. This can lead to total blindness.

What To Think About

A perimetry test is a good test to find vision loss caused by glaucoma. A perimetry test makes a detailed record of your visual fields. Baseline information, descriptions or drawings can be compared with future test results.

A perimetry test can be done quickly, but may take more than 45 minutes when both eyes are tested.

Complete the medical test information form (PDF)(What is a PDF document?) to help you prepare for this test.