A GUIDE TO THE ISOLATED DILATED PUPIL

The poorly reactive and dilated pupil observed in a comatose patient i s often thought to represent an acute third nerve palsy owing to brain herniation or aneurysm. In the well patient, however, the isolated di lated pupil is unlikely to be owing to a third nerve palsy. It is more commonly owing to other benign causes such as local iris sphincter ab normalities, pharmacologic dilation, tonic pupil syndrome, or sympathe tic irritation. This article presents a diagnostic flowchart to help t he primary care physician analyze this problem and prevent costly and unnecessary imaging of these patients.