An anisocoria produces a small relative afferent pupillary defect in the eye with the smaller pupil

Objectives: To determine whether an anisocoria can produce a relative affer ent pupillary defect of clinical importance. Material and Methods: Anisocoria and relative afferent pupillary defect wer e measured with infrared videography in three clinical experiments: 1) ever y few minutes in eight normal subjects who remained in darkness as one pupi l was dilating from mydriatic drops; 2) every 2 hours, for 8 hours in six n ormal subjects who remained in room light after one pupil was dilated with mydriatic drops; and 3) before and after dilation of one pupil in 24 patien ts with known afferent defects from optic nerve disease and who remained in room light. Results: In the presence of an anisocoria, the relative afferent pupillary defect was almost always in the eye with the smaller pupil. The results of the three experiments were: 1) In darkness, the induced pupillary defect wa s found to be related to the ratio of the areas of the two pupils (R = 0.94 2), and 0.14 log unit of pupillary defect was produced in the eye with the smaller pupil for every millimeter of anisocoria. 2) In room light, the ind uced pupillary defect was in the eye with the smaller pupil but was less th an in Experiment I and persisted throughout the 8 hours. This was presumabl y because the eye with the larger pupil had become more light adapted in th e clinic light than the eye with the smaller pupil. 3) In room light, induc ing an anisocoria in patients with preexisting afferent pupillary defect te nded to shift the pupillary defect toward the eye with the smaller pupil (R = 0.68). Conclusions: Clinically, approximately 0.1 log unit of relative afferent pu pillary defect is produced in the eye with the smaller pupil for every mill imeter of anisocoria. Therefore, the anisocoria must be larger than 2 mm in diameter difference to induce a clinically significant relative afferent p upillary defect.