questions 3

Eye Movement

Topic updated on 05/15/17 7:26pm

Introduction
  • The forebrain controls eye movement via
    • frontal eye fields (FEF) which
      • are involved in generating
        • contralateral saccades via
          • the contralateral paramedian pontine reticular formation (PPRF)
      • clinical correlate
        • right-way eyes
          • lesions at the cerebral hemispheres (e.g., stroke) that affects the FEF results in the eyes looking
            • toward the side of the lesion
        • wrong-way eyes
          • a seizure at the FEF will result in the eyes looking
            • away from the side of seizure activity
          • thalamic hemorrhages
            • for unknown reasons
  • Cranial nerves involved in eye movements
    • oculomotor nerve (CN III)
      • innervates all of the extraocular muscles except
        • superior oblique muscle
        • lateral rectus muscle
      • medial rectus → adducts eye
      • superior rectus → elevates and intorts
      • inferior rectus → depresses and extorts
      • inferior oblique → elevates and extorts
      • a lesion results in
        • horizontal and vertical diplopia
          • in cases of complete one-sided CN III palsy results in
            • ptosis
            • mydriasis
            • inability to
              • adduct, elevate, and depress the eye
            • the eye resting in an
              • down-and-out and intorted position
    • trochlear nerve (CN IV) 
      • superior oblique muscle → depresses and intorts
      • a lesion results in
        • vertical diplopia that worsens with downgaze
          • can reduce diplopia by tilting head away from the side of the lesion
    • abducens nerve (CN VI)
      • lateral rectus → abducts the eye
      • a lesion results in
        • horizontal diplopia
  • Clinical correlate
    • medial longitudinal fasciculus (MLF)
      • function
        • these are heavily myelinated fibers that interconnects the
          • oculomotor nuclei
          • trochlear nuclei
          • abducens nuclei
          • vestibular nuclei
      • lesion
        • internuclear ophthalmoplegia
          • a lesion affecting the ipsilateral MLF will impair adduction of the
            • ipsilateral medial rectus (and thus a horizontal gaze palsy)
              • notes can have nystagmus of the opposite eye for unknown reasons


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