• The pupil controls the amount of light striking the retina by acting as an aperture stop - the most light-restrictive element of an optical system. The pupillary diameter or, more precisely, the iris size is controlled by two muscles, the sphincter pupillae and dilator pupillae. Contraction of the sphincter, accompanied by relaxation of the dilator, produces pupil constriction (miosis), while contraction of the dilator, accompanied by relaxation of the sphincter, produces pupil dilation (mydriasis). These muscles are innervated by the autonomic nervous system, and controlled by central neural pathways that are influenced by retinal illuminance, viewing distance, attention, and alertness.
  • Authors

    Digital Object Identifier (doi)

    International Standard Book Number (isbn) 13

  • 9780123741981
  • Start Page

  • 549
  • End Page

  • 555