The circular opening in the centre of the iris.
In bright conditions, the pupil constricts; in dim light, it dilates.
n. the circular opening in the centre of the *iris, through which light passes into the lens of the eye. —pupillary adj.
A condition (described originally by Dr Argyll Robertson) in which the pupils contract when the eyes converge on a near object, but fail to contract when a bright light falls on the eye. It is found in several diseases, especially in locomotor ataxia and neurosyphilis, an advanced manifestation of SYPHILIS.... argyll robertson pupil
(light reflex) the reflex change in the size of the pupil according to the amount of light entering the eye. Bright light reaching the retina stimulates nerves of the *parasympathetic nervous system, which cause the pupil to contract. In dim light the pupil opens, due to stimulation of the *sympathetic nervous system. See also iris.... pupillary reflex
(Adie’s pupil) a pupil that is dilated as a result of damage to the nerves supplying the ciliary muscle and iris. It reacts poorly to light but may constrict better for near vision, with slow redilation on refixation at a distance. The tonic pupil is sensitive to dilute 0.1% pilocarpine drops, which cause marked constriction but have little effect on a normal pupil. The tonic pupil may become miotic (see miosis) over time.... tonic pupil
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