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 while you concentrate on a central point, in which you then have to press a button whenever you see the light. The lights are bright or dim at different stages of the test. Some of the flashes are purely to check you are concentrating. Your head is kept still on a chin rest and each eye is tested separately. Carried out by Humphrey Field Analyzer, the entire test takes 5-15 minutes.