Adie's pupil is a neurological disorder type of disease that affects the nervous system. The nervous system is 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 the things like sweating and salivating.
The nervous system also controls the pupil (small hole in the center of the iris) and its response to light. Normally, the pupil 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. Usually, 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.