Definition of miosis in US English:


(also myosis)


  • Excessive constriction of the pupil of the eye.

    • ‘Symptoms include nasal congestion, ptosis of one eyelid, miosis, and conjunctional hyperemia.’
    • ‘After inhalation of vapour, respiratory symptoms, dimming of vision, and miosis are generally the first clinical features to appear.’
    • ‘Although miosis was the most common symptom, severely poisoned patients developed CNS symptoms and cardiomyopathy.’
    • ‘Oral pilocarpine is contraindicated in patients with uncontrolled asthma and in patients in whom miosis is undesirable, such as patients with acute iritis or narrow angle (angle closure) glaucoma.’
    • ‘A stimulant action on the parasympathetic portion of the oculomotor nucleus (third cranial nerve) is responsible for pupillary miosis.’


Early 19th century: from Greek muein ‘shut the eyes’ + -osis.