Mydriasis - Definition

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Mydriasis is an increase in the size of the pupil, the black circle in the center of the iris, the colored part in the middle of the eye. This phenomenon typically manifests in the dark in order to adapt our vision to the lack of light by capturing more rays. Conversely, when the eye is exposed to bright light, the pupil contracts: a process we call miosis. To test pupillary light reflex we shine a light into each eye separately, making the pupil contract in the light and dilate when we take it away. Mydriasis is defined by an abnormally dilated pupil. It can affect both eyes, such as in certain drug-induced states or brain death, or just one. In the latter case, several eye conditions can be the cause, and if any neurological symptoms or impaired consciousness are detected then brain trauma is suspected, namely that there is pressure acting on a part of the brain. If these symptoms are detected, an emergency CT or MRI scan must be performed, or an ophthalmologist must be consulted.