A visual field test measures a person’s whole scope of vision. This includes both the central and peripheral, or side, vision. These tests map the individual fields of the eyes. Visual field testing requires the patient’s full cooperation, as he or she must understand the test that is to be performed and participate in the whole test so that the patient has a thorough understanding of his or her condition.
An eye test that is not as thorough as a visual field test may not measure peripheral vision. Peripheral vision is the complete horizontal and vertical range of what a person can see. Commonly called side vision, it is that part of the eyesight that a patient does not see directly but from the corners of his or her eyes.
The point of a visual field test is to detect blind spots, which may indicate illnesses of the eyes. Eye diseases include optic nerve damage, optic neuropathy, retinal disease, eye drooping, toxic exposure and damage to the eye’s inner lid, caused by overexposure to light. An eye visual field test can also detect abnormalities in the brain that cause strokes or tumors. These abnormalities not only affect the visual field, but the location of the stroke or tumor is often determined by the size, shape and location of the eye problem or defect.
A visual field test is performed by the patient covering one eye and looking straight ahead at a target object. Central vision and peripheral vision are tested individually. The doctor tests the patient’s central vision by having him or her focus on part of his or her face, such as an eye or ear. To test peripheral vision, the patient also fixates on one object, but he or she is asked to describe what can be seen from the corners of his or her eyes.
Types of visual fields testing include automated perimetry, frequency doubling perimetry, electroroetinogram and confrontational. Automated perimetry has the patient fix on a source of light so response to the presence of objects in different field view areas can be tested. Frequency doubling perimetry involves using colored vertical bars to flicker at high frequencies. If the patient cannot see the bars, optic nerve damage may be present.
An electroroetinogram measures how a patient responds to flashing stimuli, and the electrode can detect the degree of sensitivity of the retina. An overly sensitive retina can be a sign of an eye illness. The final major type of visual field test is a confrontational test. This tests peripheral vision by moving an object around a patient’s frame of peripheral vision to test response speed.