Eye Movement

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
      • may become entraped during orbital floor fractures, leading to limited vertical eye movement   
    • 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
        • bilateral MLF lesions are commonly found in multiple sclerosis 
          • causes impaired adduction of both eyes during gaze towards the opposite side