Adie's pupil is a neurological disorder—a type of disease that affects the nervous system. The nervous system—made up of the brain, spinal cord, and nerves—controls many of our involuntary bodily functions. These are reflexive actions that happen automatically, without having to think about them—things like sweating, salivating, and sneezing.
The nervous system also controls the pupil (small hole in the center of the iris) and its response to light. Normally, the pupil constricts (gets smaller) in brighter light to let less light in. In lower light, the pupil dilates (widens) to let more light in, so we can see better.
With Adie's pupil, there is an abnormal pupillary response to light. In most cases, it affects only one eye. The affected pupil is usually larger than normal and does not constrict as it should in the presence of bright light.
No one knows for sure what causes Adie's pupil. Most doctors think it's caused by a viral or bacterial infection that damages the nerves that control the pupil. Some think it may be caused by autoimmune disease, when the body's immune system attacks its own healthy tissues, like the nerves that operate the pupil.
Symptoms of Adie's pupil can include having:
Rarely, both eyes are affected. And sometimes, Adie's has the opposite effect on a patient's pupil(s), where they fail to widen adequately in low light situations.
There are also some non-eye related symptoms that are common with Adie's pupil, including: