Anisocoria is a condition in which the pupil of one eye differs in size from the pupil of the other eye. It is usually mild, constant, and not a cause for concern. However, if it happens suddenly, it may be a sign of a serious medical condition and you should see an ophthalmologist right away. The underlying cause of anisocoria can be anything from medications to neurological conditions.
An eye exam can help determine the cause and the best treatment plan. Normally, the pupil size is the same in each eye, with both eyes dilating or narrowing together. The presence of anisocoria may be normal (physiological) or may be a sign of an underlying medical condition. In most cases, anisocoria is mild, constant, and not a cause for concern.
But if it happens suddenly, this can be a sign of a serious medical condition and you should see an ophthalmologist right away. Medications that can cause this condition generally include SSRIs (selective serotonin reuptake inhibitors) used to treat depression, scopolamine transdermal patches used to treat nausea and motion sickness caused by chemotherapy, and certain eye drops for glaucoma. An abnormality of the third cranial nerve (a nerve that runs from the brain to the eye socket and controls the position of the eyelids, eye movement, and pupil size) can also cause a pupillary abnormality. A pediatric ophthalmologist or neuroophthalmologist performs a complete eye exam to assess vision, eyelid position, eye movement, and the health of the front and back parts of the eyes (among other things).
When a child is diagnosed with Horner syndrome, the doctor may order additional tests, such as radiological studies, to help look for evidence of neuroblastoma or other abnormalities in the abdomen, chest, or neck. The ophthalmologist can treat the symptoms of iritis while determining and monitoring the underlying cause of the condition. Photochromic lenses also protect the eyes from harmful UV rays and high-energy blue light, especially the eye with the larger pupil, if it doesn't react normally to light. If you notice that your pupils aren't the same size, schedule an eye exam as soon as possible to rule out any serious conditions.
The sooner you determine the cause of anisocoria, the sooner your eye doctor can recommend the most appropriate treatment plan.