What are some causes of an abnormally large (dilated or mydriatic) pupil?
After a trauma to the eye, the iris tissue can be injured causing the pupil to not constrict to bright light normally. Another possible cause is Adie’s tonic pupil syndrome. This is a condition most common in young adult females, which usually begins in one eye. The pupil is sluggish to react to light. Many people with this condition will also have diminished deep tendon reflexes and they can have trouble focusing at near. The condition is usually not associated with any more serious conditions. Some eyedrops have a dilating effect on the pupil, so eyedrop use is another cause of a dilated pupil. Finally, an abnormality of the third cranial nerve (a nerve that comes from the brain to the eye socket and controls eyelid position, eye movement, and pupil size) can cause a pupillary abnormality. In this condition, there is often ptosis (droopiness) of the upper eyelid on the same side as the dilated pupil. In addition the eye may not move normally and an older child might complain of doubl
