Pupillary reflex

Pupillary reflex is a reflex that controls the diameter of the pupil, in response to the intensity (luminance) of light that falls on the retina of the eye, thereby assisting in adaptation to various levels of lightness/darkness. A greater intensity of light causes the pupils to constrict (myosis; miosis), thereby reducing the amount of light that enters the eyes, while a lower intensity of light causes the pupils to dilate (mydriasis; mydriasis), thereby increasing the amount of light that enters the eyes.

Mechanism

The pupillary light reflex involves a direct and consensual response. The direct response involves a constriction of the pupil on the same side as the light stimulus, while the consensual response involves a constriction of the pupil on the side opposite the light stimulus. This reflex is mediated by the Edinger-Westphal nucleus, pretectal nucleus, and oculomotor nerve.

Clinical significance

The pupillary light reflex is used in clinical practice to assess the integrity of the optic nerve, oculomotor nerve, and midbrain. Abnormalities in the pupillary light reflex can indicate damage to these structures and can be a sign of various medical conditions, such as Adie's pupil, Argyll Robertson pupil, and Horner's syndrome.

See also

• Pupil
• Reflex
• Optic nerve
• Oculomotor nerve
• Midbrain

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