The child may have mild ptosis (droopiness) of the upper eyelid. In Horner’s syndrome, the pupil in the involved eye is usually smaller and does not dilate as well as the other eye. Horner’s syndrome also produces a small pupil in the affected eye. Inflammation within the eye, whether from trauma or another cause, can result in a miotic pupil. What are some causes of an abnormally small (miotic) pupil? A third cranial nerve palsy can be a sign of a potentially serious condition, and the doctor may want to consider other possibilities. In addition, the eye may not move normally and an older child might complain of double vision. In this condition, there is often ptosis (droopiness) of the upper eyelid on the same side as the 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. Some eyedrops have a dilating effect on the pupil, so eyedrop use is another cause of a dilated pupil. The condition is usually not associated with any more serious conditions. Many people with this condition will also have diminished deep tendon reflexes and they can have trouble focusing at near. This is a condition most common in young adult females, which usually begins in one eye. Another possible cause is Adie’s tonic pupil syndrome. What are some causes of an abnormally large (dilated or mydriatic) pupil?Īfter trauma to the eye, the iris tissue can be injured causing the pupil to not constrict to bright light normally. Conversely, if the difference in pupil size increases in bright lighting, then the larger (mydriatic) pupil may be the abnormal one because it is not constricting normally. If the difference in size between the pupils increases in the dark, then the smaller (miotic) pupil may not be dilating well and could be the abnormal one. One of the most important parts in the evaluation of anisocoria is determining which pupil is abnormal. How does the doctor know if the big pupil is ‘too big’ or the small pupil is ‘too small’? Based on the evaluation, the doctor may wish to perform additional tests with eyedrops or perform laboratory or radiologic testing. The doctor will evaluate the size of the pupils and how they react to bright and dim lighting. A complete eye examination by a pediatric ophthalmologist is performed and will evaluate the vision, eyelid position, how the eyes move, the health of the front and/or back portions of the eyes (among other things). How does the doctor determine whether anisocoria is due to an underlying medical problem?Ĭertain characteristics, such as when the anisocoria was first noted, whether it is more noticeable in bright or dim illumination, and whether or not there was a preceding event that could be related, will help determine the underlying cause. Typically with physiologic anisocoria, the difference in pupil size between the two eyes does not exceed one millimeter. Anisocoria that is NOT associated with or due to an underlying medical condition is called physiologic anisocoria. The amount of anisocoria can vary from day-to-day and can even switch eyes. The presence of anisocoria can be normal (physiologic), or it can be a sign of an underlying medical condition.Īpproximately 20% of the population has anisocoria. The term anisocoria refers to pupils that are different sizes at the same time. Normally the size of the pupil is the same in each eye, with both eyes dilating or constricting together. Is it normal to have pupils of different sizes? When in a bright room or outdoors the pupil usually constricts conversely when in a dark room the pupil usually dilates to allow more light to enter the eye. The empty hole in the middle, which allows light to enter the eye, is called the pupil. It is a circular muscle, similar in shape to a donut. The colored part of the eye is called the iris.

Causes of unequal pupil size