miose

Miose, also known as miosis, is the constriction of the pupil, resulting in a smaller pupil diameter. It is the opposite of mydriasis, the dilation of the pupil. The constriction is produced by the sphincter pupillae muscle in the iris, under parasympathetic control.

The neural pathway begins with retinal input that projects to the pretectal area and then to the Edinger–Westphal nucleus. Parasympathetic fibers travel with the oculomotor nerve to the ciliary ganglion and then via short ciliary nerves to the sphincter. In a normal pupillary light reflex, exposure to light prompts miosis to regulate the amount of light entering the eye while supporting near vision.

Physiological miosis occurs in bright light or during the near response (accommodation). Pharmacologic or toxic miosis can result from cholinergic drugs, organophosphates, or opioid medications, among others. Pathologic miosis may be seen in conditions such as Horner’s syndrome (often with ptosis and anhidrosis), Adie’s tonic pupil, or other disorders affecting parasympathetic innervation.

Clinically, miosis is evaluated by observing pupil size and reflexes, and by considering anisocoria, the presence of unequal pupil sizes. Management focuses on identifying and treating the underlying cause, with ophthalmologic or neurologic consultation as appropriate.