Miosis is excessive constriction of the pupil. The term is from Ancient Greek μύειν, mūein, "to close the eyes".
The opposite condition, mydriasis, is the dilation of the pupil. Anisocoria is the condition of one pupil being more dilated than the other.
== Causes ==
=== Age ===
senile miosis (a reduction in the size of a person's pupil in old age)
=== Diseases ===
Horner's syndrome
Hemorrhage into pons (intracranial hemorrhage)
Hereditary disorders
Cluster Headaches with ptosis
Iridocyclitis
Fatal familial insomnia
=== Drugs ===
Opioids such as fentanyl, morphine, heroin and methado...