mydriasis

n. abnormal widening of the pupil of the eye (Medicine)

Mydriasis is an excessive dilation of the pupil due to disease or drugs. Normally, pupil dilates in the dark and constricts in the light. A mydriatic pupil will remain excessively large, even in a bright environment. It is occasionally referred to as a "blown pupil."The opposite, constriction of the pupil, is called miosis.
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Mydriasis /my·dri·a·sis/ [Gr.] dilatation of the pupil. my·dri·a·sis n. Prolonged abnormal dilation of the pupil of the eye induced by a drug or [more]Mydriasis - Community and Resources

Noun
1. reflex pupillary dilation as a muscle pulls the iris outward; occurs in response to a decrease in light or certain drugs
(hypernym) reflex, instinctive reflex, innate reflex, inborn reflex, unconditioned reflex, physiological reaction

(n.)
A long-continued or excessive dilatation of the pupil of the eye.