A visual field test measures how much 'side' vision you have. It is a straightforward test, painless, and does not involve eye drops. Essentially lights are flashed on, and you have to press a button whenever you see the light. Your head is kept still and you have to place your chin on a chin rest. The lights are bright or dim at different stages of the test. Some of the flashes are purely to check you are concentrating.
Each eye is tested separately and the entire test takes 20-30 minutes depending on the type of visual field test performed. The most common reason for performing a threshold visual field test is to evaluate the visual field as a potential risk factor for glaucoma. After examining the eye health and the optic nerve health in particular, measuring the intraocular pressure, and evaluating the results of visual field testing, Dr Lewis will discuss with the patient whether or not there is suspicion of glaucoma.