Pupil

Aka: Pupil, Pupil Disorder

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II. Anatomy

  1. See Pupil Constriction (Miosis) for Neuroanatomy of Pupil Constriction
  2. Variable sized circular hole in pigmented iris
  3. Images
    1. EyePupillaryReactionNeuroPath.png
    2. EyePupillaryReaction.png
  4. Pupil "Hole" or aperture size controlled by 2 Muscles
    1. Sphincter pupillae
      1. Circular Muscle constricts pupil (Miosis)
      2. Parasympathetic fibers on CN3 from Edinger-Westphal Nucleus innervate the ciliary Ganglion
    2. Dilator pupillae
      1. Radial Muscle dilates pupil (Mydriasis)
      2. Sympathetic inputs via:
        1. Hypothalamus
        2. Ciliospinal center of Budge and Waller

III. Physiology

  1. Pupil is analogous to a camera aperture
    1. Shutter aperture decreases in size under bright light conditions and for sharper focus
    2. Pupil constricts under bright light and with near focus (e.g. reading) known as accomodation
  2. Optic Nerve (CN 2)
    1. Transmits visual signals not only to the visual cortex
    2. Transmits signals via a reflex loop to the pretectal nucleus
      1. Signals then travel onto the Edinger-Westphal Nucleus on each side of the Midbrain
      2. Shining light in one eye will result in a signal to both Edinger-Westphal Nucleii
      3. Signals are then transmitted to the ciliary Ganglion and along the course of Oculomotor Nerve
  3. Oculomotor Nerve (CN 3)
    1. Innervates ciliary Muscle (iris constrictor), resulting in Pupil Constriction
    2. Accomodation (near Vision) also results in signals to the Edinger-Westphal Nucleus
      1. However those signals arise from the visual cortex
    3. Syphilitic Pupil (Argyll-Robertson Pupil, Prostitute's Pupil)
      1. Affected pupil does not react
        1. Lesion in the Midbrain blocks signals from the pretecal nucleus
      2. Syphilitic Pupil does accomodate
        1. Signals follow a different pathway from the visual cortex
    4. Brainstem Herniation
    5. . Oculomotor Nerve (CN 3) is easily compressed
        1. Results in a dilated pupil that does not react (Blown Pupil)
      1. Parasympathetic fibers from the Edinger-Westphal Nucleus to the ciliary Muscle
        1. Found on the outside of the Oculomotor Nerve (CN 3),
        2. Parasympathetic fibers are first to be injured when CN 3 is compressed

IV. Findings

  1. Pupil Normal in
    1. Conjunctivitis
  2. Pupil size changes
    1. Pupil Constriction (Miosis)
    2. Pupil Dilation (Mydriasis)
  3. Pupil distortion
    1. Posterior synechiae
      1. Inflammatory adhesion between lens and iris
    2. Tear drop-shaped pupil
      1. Suggests Globe Rupture with iris prolapse
  4. Pupil fixed, mid-dilated, slightly irregular
    1. Acute Glaucoma
  5. Absent Pupillary Light Reflex
    1. Structural lesion
    2. Hypothermia
    3. Barbiturate or Opiate Overdose

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