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PATIENTS

WHAT IS THE VISUAL FIELD AND HOW IS IT TESTED?
by Dr. John Mark De Leon

A visual field (or perimetry) is an indispensable test for diagnosing and monitoring glaucoma. The test maps out one’s scope (or field) of vision and usually takes about 5-15 minutes per eye. It tests each eye’s central vision (what one sees looking straight ahead looking at a target) and peripheral (side) vision (the rest of what one sees at the sides when looking at a target) which is usually affected first by glaucoma. Each eye is tested separately since the visual fields of both eyes overlap centrally so blind spots in one eye may not be noticed by the patient since the other eye’s vision could compensate for this. This test can detect these peripheral blind spots which develop discretely and cannot be noticed by the patient especially in the early stages of glaucoma. This test is very subjective so results will depend on the patient’s alertness, cooperation, and proper instructions from the technician assisting the patient. Results of the test support the diagnosis of glaucoma if it correlates with other parts of the eye examination (e.g. eye pressure check, optic disc evaluation, etc.) that also point to glaucoma. The diagnosis of glaucoma cannot be entirely made on visual fields alone. This test is also very important because it can monitor if glaucoma, once diagnosed, is stable or getting worse so tests will have to be done periodically so they can be compared with one another.