A visual field test measures how much 'side' vision you have out of eaqch eye. It is a straightforward test, painless, and does not involve eye drops. Essentially light and dark bars of light are flickered on and off, 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 light bars are bright or dim at different stages of the test. Some of the flickers are purely to check you are concentrating and fixating on the center target.
Each eye is tested separately and the entire test takes 15-25 minutes. The testing is carried out by a computerised machine, called a Humphrey FDT. FDT stands for Frequency Doubling Technology, which is the more current testing protocol for visual field testing by the Humphrey company.