Your visual field is how wide of an area your eye can see when you focus on a central point. Visual field testing is an important part of regular eye care.
The Humphrey Field Analyzer test measures sensitivity across your field of vision, indicating how it may be changing and whether or not you have a normal visual field. There are a wide range of reasons you are being asked to perform the test. For example, glaucoma screening and / or monitoring or checking reduced vision.
To monitor progress and preserve vision, it is essential to undergo visual field tests as frequently as advised by your eye doctor.