What is pupil dilation?

The pupil is the black spot at the very center of your eye, surrounded by the colored area known as the iris. The iris is made up of small muscle fibers that control the size of the pupil, thereby controlling the amount of light allowed to reach the retina, the sensory area at the back of the eye. Pupils get smaller, or constrict, with bright light levels, and enlarge, or dilate, with low or dim light. Changes in pupil size also occur with focusing your eyes and in response to emotion.

Eye Problems Spotlight

Pupil dilation can also result from a variety medications or drugs. Eye care professionals often take advantage of eye drops that cause pupil dilation so they can get a better look at the back of the eye during an eye exam. In most other circumstances, pupil dilation from medications or drugs is considered a side effect. Medications and drugs that can cause pupil dilation include cough and cold medications, decongestants, amphetamines, cocaine, lysergic acid diethylamide (LSD), and marijuana.

Poisonings can also cause pupil dilation. Pupil dilation that results from poisonings, medications, and drug use typically affects both pupils equally, unless it is from eye drops that are used only in one eye. It is generally temporary.

Some neurologic conditions, such as stroke, tumor, or brain injury, can also lead to pupil dilation, which can occur in one or both eyes. Pupils that do not respond to light or other stimuli are called fixed pupils. Often, abnormally dilated pupils are also fixed pupils.

Pupil dilation or unequally sized pupils can occur with serious conditions such as head trauma, brain tumors, stroke, or poisoning. These conditions are medical emergencies. Seek immediate medical care (call 911) if you have pupil dilation as a result of head trauma or in association with other symptoms.

If your pupil dilation is persistent or causes you concern, seek prompt medical care.


What other symptoms might occur with pupil dilation?

Pupil dilation may accompany other symptoms, which vary depending on the underlying disease, disorder or condition. Pupil dilation with fixed or unequal pupils, as well as unequally sized pupils, are often the most serious symptoms.... Read more about pupil dilationsymptoms


What causes pupil dilation?

Pupil dilation can be a normal reaction to low light or emotion. When not part of a normal pupil response, pupil dilation can be caused by drugs, medications, poisons, brain injury, or disease.... Read more about pupil dilationcauses

Medical Reviewer: All content has been reviewed by board-certified physicians under the direction of Rich Klasco, M.D., FACEP. Last Annual Review Date: May 2, 2011 Copyright: © Copyright 2011 Health Grades, Inc. All rights reserved. May not be reproduced or reprinted without permission from Health Grades, Inc. Use of this information is governed by the HealthGrades User Agreement.

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