This is a neurologic disorder in which one eye becomes dilated. Most patients have no symptoms or visual complaints, but a friend points out that one of their pupils is now much larger than the other. Also, the pupil does not seem to constrict normally with light. An Adie’s pupil usually occurs from damage to one of the nerve clusters behind the eye (inside the eye socket) that controls pupil constriction. This damage can occur from an otherwise harmless viral infection such as a common cold. The problem is usually temporary and goes away after a few months. The opposite condition is called Horner’s syndrome. Horner’s causes pupil constriction and is potentially dangerous.