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Anatomy of the pupillary reflexes

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

The size of the pupils depends on the balance of sympathetic and parasympathetic activity supplying the iris:

  • sympathetic activity tends to dilate the pupil
  • parasympathetic activity tends to constrict the pupil

The pathway of the pupillary light reflex consists of:

  • retinal receptor cells
  • bipolar cells
  • ganglion cells
  • optic nerve and tract
  • pretectal nucleus of the high midbrain
  • Edinger-Westphal nucleus
  • efferent two neurone pathway via the oculomotor nerve
  • constrictor muscle of the iris

It should be noted that the lateral geniculate nucleus of the thalamus and the cerebral cortex are not involved in the pupillary reflexes. Hence a patient who is cortically blind will have intact light reflexes.

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