Because it has no noticeable symptoms, glaucoma is a difficult disease to detect without regular, complete eye exams.

One particular test, called a visual field test (or perimetry test), measures all areas of your eyesight, including your side, or peripheral, vision. A visual field test can help find certain patterns of vision loss and is a key way to check for glaucoma. It is very useful in finding early changes in vision caused by nerve damage from glaucoma.

To take this painless test, you sit at a bowl-shaped instrument called a perimeter. While you stare at the center of the bowl, lights flash. Each time you see a flash you press a button. A computer records the location of each flash and whether you pressed the button when the light flashed in that location. At the end of the test, a printout shows if there are areas of your field of vision where you did not see the flashes of light. This test shows if you have any areas of vision loss. Loss of peripheral vision is often an early sign of glaucoma.

Visual field testing is used together with the clinical exam and HRT testing to determine if you have glaucoma or if your glaucoma is worsening. Visual field testing is usually done at least once or twice a year or more if your disease severity warrants closer surveillance.