What does miosis mean?
Miosis is the narrowing or constriction of the pupil, the small opening in the center of the iris. In its medical sense, it describes an unusually small pupil, sometimes called pinpoint pupils, which can result from medications such as opioids, injuries or diseases of the eye, and certain neurological conditions. The pupil also constricts naturally in response to bright light, allowing the eye to regulate the amount of light reaching the retina. Clinicians use the term when describing an abnormal finding during an examination, and its significance depends on whether one pupil or both are affected and whether the pupils are equal. Miosis is the opposite of mydriasis, which means dilation of the pupil. Because abnormal constriction can provide an important clue about a patient’s condition, accurate recognition of miosis is valuable in medicine and emergency care.
nounMiosis is the abnormal or excessive constriction of the pupil of the eye, making it smaller than normal. It may result from certain medications, eye disorders, neurological conditions, or exposure to bright light.
- Abnormal or excessive constriction of the pupil of the eye.
- The physiological narrowing of the pupil in response to bright light.
"The doctor noted miosis in both pupils during the examination."
"Opioid intoxication can produce miosis, together with drowsiness and slowed breathing."
"The pupils showed miosis when the examination light was switched on."
The plural is used when referring to separate instances of pupil constriction or multiple cases of the condition.
"The examinations revealed mioses in both pupils."
Miosis turns the pupil into a pinpoint: a tiny opening that lets less light reach the retina.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does miosis come from?
The word comes from Greek mýsis, meaning “blinking” or “closing of the eyes,” referring to the narrowing of the pupil or the eye. It entered English through scientific usage, where it became established as a medical term for constriction of the pupil. The related adjective miotic describes something that causes this constriction or can be used to produce it.
Related word forms
How miosis is actually used
Miosis is primarily a medical term. In clinical descriptions, it may be used for either an abnormal pathological finding or the normal pupil response to bright light, so context is important.
Easily confused with miosis
Miosis is excessive constriction of the pupil, whereas mydriasis is abnormal or excessive dilation of the pupil.
Miosis refers to pupil size, while myopia is the condition in which distant objects appear blurred because light focuses in front of the retina.