A physiologic fluctuation in threshold levels exists in automated perimetry, which is greater in glaucoma and ocular hypertensive patients than in normal subjects. Fluctuation increases with greater eccentricity from fixation and in areas of reduced retinal sensitivity. Other factors related to automated perimetry testing potentially may influence threshold fluctuation including: a learning effect, reliability, pupil size, age, and the mode of stimulus presentation. Statistical software may aid in analyzing both the single field and the changes between successive fields. However, statistical programs cannot replace physician judgment, and all factors that may influence threshold levels should be considered when interpreting automated visual fields.