What does mydriasis mean?
Mydriasis is the medical term for abnormal dilation of the pupil, making one or both pupils unusually large. It can result from medications, eye disorders, injury, or neurological conditions, and it may be an important clinical sign when the pupils are unequal in size. The term is distinguished from miosis, which denotes abnormal pupil constriction, and from the normal widening of pupils in low light. Mydriasis is also relevant to eye examinations because medicines used to dilate the pupils can produce temporary blurring and sensitivity to light. Although general speakers often use the descriptive expression “dilated pupils,” mydriasis is preferred in medical reports, diagnoses, and discussions where abnormal pupillary dilation is specifically meant.
nounAbnormal dilation of the pupil of the eye, often resulting in unusually large pupils. It may arise from various neurological, ocular, or drug-related causes.
- Abnormal dilation of the pupil of the eye.
"The clinician noted bilateral mydriasis before administering the eye drops."
"The scan showed unilateral mydriasis, which prompted further neurological assessment."
"The medication caused mydriasis and temporary blurred vision."
Rare; the singular form is normally used in clinical writing even when several cases are discussed.
"The differential diagnosis included several rare causes of mydriases."
A dilated pupil can be a medical clue: unequal pupils may help clinicians assess a possible neurological emergency.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does mydriasis come from?
The word comes from Greek mydríasis, meaning dilation of the pupil. It derives from mýdron, an ancient Greek term for the pupil, which is also associated with the larger, central part of the eye. The modern medical term entered English in the 19th century with the development of ophthalmological and neurological terminology.
Related word forms
How mydriasis is actually used
This is a specialist medical term, used chiefly in clinical and ophthalmological contexts. It should not be used to describe the normal dilation of pupils in darkness.
Easily confused with mydriasis
Mydriasis is abnormal dilation of the pupil, whereas miosis is abnormal constriction of the pupil.