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. You have to rest 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.
You need to bring your reading or bi-focal glasses you have. (But always bring your distance and reading glasses to every eye clinic visit.)