1. reflex contraction of the sphincter muscle of the iris in response to a bright light (or certain drugs) causing the pupil to become smaller; [syn: light reflex, pupillary reflex, miosis, myosis]
WordNet (r) 3.0 (2006):
light reflex
n 1: reflex contraction of the sphincter muscle of the iris in
response to a bright light (or certain drugs) causing the
pupil to become smaller [syn: light reflex, pupillary
reflex, miosis, myosis]