Long-term fluctuation. The variability between two visual fields performed sequentially on the same eye that cannot be attributed to pathologic change. The test–retest interval is typically days to months or longer.

Short wavelength, automated perimetry (SWAP).Visual field test in which short wavelength-sensitive (blue) cones are isolated by using blue light stimuli projected on a yellow background. Also called blue-on-yellow perimetry.

Frequency doubled perimetry.Visual field test in which stimuli are alternating high-frequency contrast bands.

Depression. A reduction in expected (normal) sensitivity. Scotoma. A localized defect or depression within the visual

field.

Absolute defect. A field defect that persists when the maximum stimulus of the testing apparatus is used.The normal blind spot is an absolute scotoma.

Relative defect. A field defect that is present to weaker stimuli but disappears when tested with brighter stimuli. A defect that is not absolute (see Fig. 10-4).

Candela per square meter (cd/m2). The international unit of luminance.

Apostilb. 0.1 millilambert 3.183 cd/m2.

Log unit. Logarithm base 10 of the luminance in apostilbs. Decibel. One-tenth of the log unit.

Theory of visual field testing

The purpose of visual field testing is to define the topography of the island of vision to recognize any variation from normal. It is used to detect abnormalities and to follow abnormalities while the patient is under observation or treatment. The visual field is tested by adapting the eye to the background luminance and then presenting a stimulus that is some degree brighter than the background at a given position in the field. The ability of the patient to perceive the stimulus may be tested kinetically, statically, or with some combination of the two techniques.