What is a visual field?
The visual field is everything you see looking straight ahead, including your side and central (straight ahead) vision. Since you probably use both your eyes at all times, you may not notice any changes in one eye's visual field unless you close the other eye.
Eye diseases such as optic nerve damage or glaucoma can affect only one eye.You may not know that there is a problem unless each eye is tested separately.
How is a visual field done?
During a visual field test, one eye is temporarily patched. You are asked to look straight ahead at a fixed space and to watch for targets to appear in your field of vision.
Because it is also a test of your side vision, it is very important that you keep looking straight ahead. Do not move your eyes to look for the target but wait until a light appears; in your side vision.
There are two kinds of tests:
1. Moving targets: Targets are moved from where you can't see them (beyond your side?vision) in towards the center of vision until you do see them. The test can be done with either a black screen on a wall (tangent testing) or with a large bowl-shaped instrument (Goldmann testing)
2. Fixed Targets: This test uses small targets that appear bright or dim but do not move (computerized static perimetry). You will sit in a chair facing either a bowl-shaped instrument or a computer screen. The targets appear briefly.
What do you need to do during the test?
Keep your eye steady, looking straight ahead, and wait for the test target to come into your sight Don't move your eye to look for it;
Promptly press the machine's button (or answer aloud if asked) as soon as you think you see the target;
Don't worry about how well you are doing the test. The test may seem difficult.
If you think you need to rest during an examination, tell the technician.
What are common complaints about visual field testing?
People sometimes complain that the visual field test is "too hard," or say "I keep falling asleep," or "I feel like I'm being hypnotized and don't really know if I am seeing these little dots."
These complaints result from certain kinds of very sensitive tests. The tests present dimmer and dimmer targets until they reach the limit of what your eye can see.
Sometimes if a test seems very hard it means the computer keeps making the targets harder and harder to detect and that your eye is very healthy!
Why bother with visual field tests?
The visual field examination is important to detect many diseases that affect the eye, optic nerve or brain. One way for your ophthalmologist to tell if you have glaucoma is to detect the small blind spots that begin to appear in the early stage of the disease. By repeating the test in the future, your physician can then tell if the small blind spots are getting larger The visual field test provides information which no other test can. Your ophthalmologist will interpret the results and discuss them with you.