Commonly the patient is asymptomatic with anisocoria being noticed by a friend or relative. The cause of this benign condition is unknown, but the lesion is probably in the ciliary ganglion and post-ganglionic parasympathetic denervation is a feature. In the initial stages the affected pupil is dilated, reacts poorly to light, but retains a slow tonic near response (light-near dissociation). Over a period of months and years the mydriasis diminishes and the abnormal pupil eventually becomes smaller (miotic) than the normal side.
