Benign Anisocoria is related to Gender

Abstract

Benign or physiologic anisocoria (BA) refers to a small difference in the size of the two pupils, which is likely caused by asymmetry of sympathetic nervous system (SNS) innervation. Here I measure BA in a large sample of young adults and find that its distribution varies with gender. Females presented a small but significant bias to the right (right pupil larger than left), whereas males exhibited a larger and significant bias to the left (left pupil larger than the right). The sex difference was primarily attributable to right-pupil size, which was significantly larger for females than males (no significant difference in left-pupil size). Based on the premise that BA is caused by SNS asymmetry, these results suggest that SNS lateralization is more common in males than females and biased to the opposite side of the brain. Future studies that measure bilateral brain activity in addition to pupil size and other measures of SNS function (e.g., electrodermal response) are needed to validate the relationship between BA and SNS lateralization.