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What Is Mydriasis?

Optometrists often induce mydriasis when examining the eye.
People with mydriasis have abnormally dilated or large pupils.
Normally, a person's pupils contract when light is bright, but mydriasis can stop this process.
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  • Written By: Tricia Ellis-Christensen
  • Edited By: O. Wallace
  • Last Modified Date: 25 September 2014
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When the eye’s pupils get larger or smaller, this may be more formally called dilation and constriction. If this response fails to work as normal, sometimes people will have abnormally dilated or large pupils. This condition, which can occur under a variety of circumstances, is known as mydriasis.

Mydriasis sometimes represents failure for the eyes to respond as they normally would to light as a result of a congenital or genetic syndrome. Genetic causes are fairly uncommon, but there are many causes of mydriasis that occur with much greater regularity. Factors that result in extreme pupil dilation can still be varied in nature.

Anyone who has ever watched a medical show like ER or Gray’s Anatomy may remember the phrase doctors often say when evaluating a very ill patient: “the pupils are blown.” This is descriptive of pupil dilation as might often occur with severe head injury. Damage has occurred to muscles that control eye dilation, and even in extreme light the pupil remains open. It should be noted that unlike in medical shows, a blown pupil doesn’t necessarily indicate death. Also sometimes mydriasis occurs because of eye injury and these injuries could be reparable.

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It certainly doesn’t take a head injury to induce abnormal pupil dilation. There are many drugs, legal and not legal, that can result in the condition. Drugs that might temporarily induce excessive dilation and failure to normally respond to light with contraction of the pupil include many hallucinogenic drugs, a number of amphetamines, a variety of anti-depressant drugs in very large doses, and sometimes antihistamines. Occasionally drug withdrawal creates this issue, and those who are withdrawing from long term use of a variety of opiates might have very wide pupils as a symptom.

Drugs aren’t the only way in which mydriasis might occur. Certain fairly normal states of being may temporarily interfere with the muscles that control dilation and constriction. In particular things like having an orgasm or being pregnant might induce temporary significant dilation.

Sometimes doctors specifically want to induce mydriasis so that they can carefully examine the eyes for diseases. This is common in many optometrist and ophthalmologist examinations. Drops are used which cause the eyes to dilate. The condition can feel very odd, though it isn’t usually painful, and people must wear dark glasses for several hours afterwards to protect the eyes from too much light exposure. A similar tactic may be adopted when treated mydriasis of other causes. First cause must be identified, remedied when possible, and eye protection is recommended in bright light while the condition persists.

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