Medically reviewed by Johnstone M. Kim, MD Mydriasis occurs when the pupil remains dilated (widened) and doesn't respond to light changes in an environment. It can happen due to an injury, medications ...

Iris Coloured part of the eye that contains muscles. These relax or contract to adjust the size of the pupil. Controls how much light enters the pupil. Pupil Hole in the middle of the iris.