Visual field testing, also known as perimetry testing, is a diagnostic tool that measures a patient’s scope of vision, including side, or periphery, vision. The test is often used to detect and monitor optic nerve damage and subsequent peripheral vision loss due to glaucoma.

Visual field testing is painless and generally takes less than 30 minutes to complete. The test is normally performed one eye at a time. During testing, the patient rests his or her chin on a small cup and looks inside a bowl-shaped instrument called a perimeter. While the patient stares straight ahead to the center of the bowl, a series of flashes appears. Each time the patient sees a flash, he or she clicks a handheld button. The machine records these responses (or lack of responses), and at the conclusion of the test, generates a report detailing possible patterns of vision loss.