The pupil, the black spot in the center of the eye, is essentially a hole that allows light into the eye. The pupil enlarges and constricts as the muscles attached to it respond to stimuli such as light, which shrinks pupils. Darkness and stress enlarges them. Many medical conditions and medications can also cause dilated pupils, also known as mydriasis, in one or both eyes.
Drugs
A number of medications, legal and illegal, and poisons cause dilated eyes, or pupillary enlargement. Normally both pupils enlarge in response to drugs. Cocaine, methamphetamines, amphetamines, ecstasy, marijuana and alcohol can all cause pupil dilation. Poisons such as water hemlock and jimson-weed and carbon monoxide also cause pupil dilation. Medications containing atropine, ephedrine, such as cold medications and ephedra, used as an appetite suppressant, also can lead to pupil enlargement. Tricyclic antidepressants and antihistamines are also among the possible culprits for causing mydriasis, Family Practice Notebook.com reports. Medications such as atropine, phenylalanine, tropicamide and scopolamine are used to dilate eyes for examination or surgery.
Diseases
Pupil dilation can results from many different diseases. Eye problems such as uveitis, or inflammation of the center part of the eye; iritis, or inflammation of the colored part of the eye; pseudoexofoliation syndrome, which is characterized by accumulation of flakes of material in the iris near the pupil; and narrow angle glaucoma all can cause unilateral pupil dilation. Adie's tonic pupil, a dilated pupil that responds poorly to light, results from damage to the ciliary ganglion, through which nerves that cause papillary constriction pass. Sinusitis can occasionally cause blood clots to form in the sinuses; this causes fixed, dilated pupils, the University of Maryland Medical Center reports.
Brain damage caused by aneurysm, stroke or tumors that affects the cranial nerves that enervate the eye may result in an enlarged pupil as well. Sudden onset of a dilated pupil with pain in the eye should be considered an intracranial aneurysm until proven otherwise, Pacific University of Oregon states. Brain herniation and brain death result in bilateral fixed and dilated pupils.
Trauma
Trauma can cause pupil dilation. Injury to the pupil or damage to the nerves that regulate pupil movement caused by head injury can cause dilation of one or both eyes.
References
- White House Initiative on Educational Excellence for Hispanic Americans: Specific Drugs and Their Effects
- West Virginia Agriculture: Avoid Poisonous Plants
- Family Practice Notebook.com: Mydriasis
- Pacific University of Oregon School of Optometry: Pupil Anomalies: Reactions and Red Flags
- West Metro Ophthalmology: Adie's Tonic Pupil
