The presence of a miotic eye with an associated ptosis raises the possibility of Horner syndrome, although isolated concomitant ptosis and simple anisocoria must be considered. This often is referred to as pseudo-Horner. Any condition resulting in an inflammatory response within the anterior chamber may cause spasm within the sphincter muscle, resulting in anisocoria. Acute closed-angle glaucoma results in a red painful eye and visual disturbance. In this condition, the pupil tends to be fixed in mid position, with an impaired light reflex that may simulate interruption of the parasympathetic nervous system.
Prosthetic eyes have yet to show a brisk light reflex.
Other important causes of irregular pupils with poor light reflex are congenital malformation of the iris, postoperative changes, and posttraumatic mydriasis due to tears in the iris and its sphincter muscle. Typically, patients with anisocoria due to local causes have a painful red eye with a small pupil and visual disturbance, including direct and consensual photophobia. Differential diagnosis of the dilated pupil is relatively small. Once angle-closure glaucoma and a mechanically damaged sphincter muscle are eliminated from the possible etiologies, dysfunction of the parasympathetic nervous system clearly has occurred. Such pupils are dilated and show poor reactivity.