Increase of the short-term fluctuation of the differential light threshold around a physiologic scotoma.

Because determination of the differential light threshold of a visual field is a psychophysiologic test, the results can be subject to variation. This scatter measured during a single examination is usually called the short-term fluctuation. Increases of the short-term fluctuation were thought to occur primarily in abnormal visual fields; however, we found an increase of the short-term fluctuation in normal visual fields when the measurements were made at the border of a physiologic scotoma, such as the blind spot. These results suggest that an increase of the short-term fluctuation may be mainly related to measurements done with any static perimeter at the border of a depression of the island of vision.