Anisocoria. Variation and clinical observation with different conditions of illumination and accommodation.

Variations in anisocoria in light and dark conditions are used to help diagnose normal and pathologic conditions; however, there have been few observations of anisocoria in different lighting and accommodative conditions. The authors measured pupil size photographically in a group of normal subjects examined in six conditions that were controlled for illumination and accommodation. Greater variation and average extent of anisocoria were found in conditions that resulted in larger pupil size. A subset of subjects repeated several sessions. For this group, the average value of anisocoria and variability tended to be greater in dark conditions. These results show that the observation of anisocoria varies under different conditions, and they suggest careful consideration of conditions used clinically to assess pupil equality. Our analysis shows that for a given observation threshold, conditions that produce even modest changes in variability can cause dramatic changes in the probability of observing anisocoria.