How is Pupil Dilation Caused

There are a lot of drugs that cause pupil dilation. Pupil dilation may also be caused due to serious diseases like tumor or stroke. It is wise to be aware of the drugs that cause dilated pupils as a side effect. The pupil is located in the eye. It is black in color and surrounded by the iris. The pupil size is controlled by the muscle fibers present in the iris. Dilation of the pupil or mydriasis may be caused due to drugs or disease. The normal pupil will dilate in the dark and constrict in the light. A dilated pupil does not constrict in the dark or light.

The drugs that cause pupil dilation:

1. Atropine
2. Antihistamines like chlorpheniramine or diphenhydramine
3. Amphetamines
4. Eye drops
5. Decongestants
6. Lysergic acid diethylamide
7. Cocaine
8. Marijuana
9. Methamphetamines
10. Heroin or narcotic withdrawal

Pupil dilation if caused by side effects of drug usage will occur in both eyes. Dilation of only one pupil may be due to the disease called Adie’s syndrome. One pupil will contract more slowly when exposed to light than the other. This may be due to an inflammation of the nerves or malfunction of the fibers which control dilation. If only one pupil is dilated, it could mean brain injury, stroke or tumor.

Parents are usually warned by drug education councils about the relationship between illegal drugs and dilated pupils. If the children use drugs, then their pupils will be dilated. Methamphetamines, cocaine, mescaline and peyote cause pupil dilation. These drugs excite the nervous system. The signals from the brain are mixed and cause dilated pupils, euphoria, increased heart rate, emotional disturbances and drastic changes in behavior.

People who have had an eye examination may be aware of eye drops that doctors administer to enlarge the pupil. The dilated pupil allows the doctor to have a proper and clear look inside. The eyes will remain dilated for a few hours depending on the medicine.

The dilator muscles open the pupil. The sphincter muscles close the pupil. There are two types of drugs that dilate the pupil. One type stimulates the dilating muscles. The other type paralyzes the sphincter muscles. The ophthalmologists use medicines such as tropicamide, cyclopentolate, homatropine and atropine. The drug which paralyzes the sphincter muscle is phenylephrine. Eye doctors mix these drugs usually. Other non-ophthalmic drugs that cause pupil dilation are muscle relaxants, antihistamines, tricyclic antidepressants, caffeine, amphetamines, cocaine and psychedelics.

Both legal and illegal drugs may cause pupil dilation. Poisons such as jimson weed, carbon monoxide and water hemlock may cause dilated eyes. Ephedra which is used to suppress appetite may cause pupil dilation. Eyes are dilated before surgery using drugs such as scopolamine, tropicamide or atropine.

Reference: medical health

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