Visual acuity measures central vision; visual fields measure peripheral vision. Defects in the visual fields can be detected with simple screening tests or with more complex formal techniques.
A simple screening technique for detecting small, dense defects near fixation uses the Amsler Grid.
Another simple screening technique is called confrontation visual field testing.
Formal visual field testing involves the use of a bowl perimeter. Bowl perimeter testing is normally performed only by ophthalmologists and optometrists. Here is how to do formal visual field testing.