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Muscles of Eye

Topic updated on 11/13/17 6:24pm

Introduction
 
Muscles of the Eye
Muscle Innervation
Major Function
Superior rectus
  • Oculomotor nerve (CN III)
  • Elevation and intorsion
Inferior rectus
  • Oculomotor nerve (CN III)
  • Depression and extorsion
Lateral rectus
  • Abducens nerve (CN VI)
  • Abduction
    • lateral movement of the eye
Medial rectus
  • Oculomotor nerve (CN III)
  • Adduction
    • medial movement of the eye
Superior oblique
  • Trochlear nerve (CN IV)
  • Depression and intorsion
Inferior oblique
  • Oculomotor nerve (CN III)
  • Elevation and extorsion
 
Cranial Nerve Palsies
  • Oculomotor nerve palsy (3rd nerve palsy)
    • results in paralysis of the innervated extraocular muscles 
      • therefore, the lateral rectus and superior oblique muscles are preserved 
        • leads to a "down and out" position of the eye at rest with additional findings depending on the location and cause of the lesion
        • other findings that can be seen with a third nerve palsy include
          • ptosis due to the oculomotor nerve's innervation to the levator palpebrae muscle
          • mydriasis due to the parasympathetic fibers of the oculomotor nerve innervating the iris sphincter muscles
    • etiologies
      • compression
        • causes
          • aneurysms (e.g., posterior communicating artery aneurysm)
          • uncal herniation
        • pathogenesis
          • first compresses the outer components of the 3rd nerve (where the parasympathetic fibers are)
        • presentation
          • painful "down and out" eye with a "blown pupil" (mydriasis)
      • vascular disease
        • causes
          • diabetes
          • hypertension
          • hyperlipidemia
        • pathogenesis
          • ischemic damage to the interior components of the nerve
        • presentation
          • painless "down and out" eye with sparing of the pupil
  • Trochlear nerve palsy (4th nerve palsy)
    • results in paralysis of the superior oblique muscle, which normally intorts and depresses the eye
      • results in hypertropia (eye elevation) and extorsion of the eye
    • etiologies
      • head trauma
        • the trochlear nerve is thin and has a long course from the brainstem to the eye, putting it at an increased risk for shear injury during head trauma
    • presentation
      • head tilting away from the affected eye
        • corrects the extorsion
      • chin tucking and slightly looking upward
        • corrects the hypertropia
  • Abducens nerve palsy (sixth nerve palsy)
    • results in paralysis of the lateral rectus muscle, which normally abducts the eye
    • etiologies
      • increased intracranial pressure (e.g., intracranial tumors, pseudotumor cerebri, and hydrocephalus)
        • the abducens nerve has a long course over the clivus and petrous bone
          • therefore, it is susceptible to experiencing downward traction in the setting of space-occupying lesions
    • presentation
      • horizontal diplopia


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