EFFECT OF LIGHT ON THE PREVALENCE OF SIMPLE ANISOCORIA

Purpose: Because simple anisocoria is believed to decrease in bright l ight, the authors determined the prevalence of simple anisocoria under different lighting conditions. Methods: The authors measured the pupi l size of 104 healthy subjects with infrared videography at four clini cally accessible light levels: darkness; darkness with a hand-held lig ht shining from below; room light; and room light with the hand light shining from below. Results: Of the 104 subjects, 40 (38%) were men an d 64 (62%) were women. The ages ranged from 12 to 71 years (mean, 36.3 +/- 12.5 years). The mean decrease in pupillary diameter from darknes s to the brightest condition was 1.89 mm. Based on the traditional def inition of a pupillary diameter difference of 0.4 mm or greater, the p revalence of simple anisocoria decreased from 18% in darkness to 8% in room light with the handheld light shining from below. The prevalence of anisocoria varied considerably when other definitions were used. R epeated measures analysis of variance showed that pupillary area diffe rence decreased with brighter conditions (P = 0.026). However, the rat io of the pupillary areas did not change with brighter conditions (P = 0.666). Conclusions: The prevalence of simple anisocoria decreases wi th brighter conditions based on pupillary diameter difference. However , this decrease is not apparent when anisocoria is expressed as pupill ary area ratio. Those clinicians who measure pupils will find that sim ple anisocoria decreases in bright light, However, with gross observat ion where perception of an anisocoria may be related more to the ratio of the pupillary areas, simple anisocoria may not seem to change much with brighter conditions.