II. Causes

  1. See Extraocular Movement
  2. Cerebrovascular Accident affecting Brodmann's area 8
    1. Conjugate deviation toward the side of the lesion (Eyes look toward the lesion)
    2. For example, eyes look to the right-sided CVA lesion as they are unable to look to the contralateral side
    3. Innervation of left-sided CN 6 nucleus is interrupted, as is Lateral Gaze Center and Medial Longitudinal Fasciculus
    4. Loss of Conjugate Gaze with interrupted Medial Longitudinal Fasciculus
      1. No signals passed to ipsilateral, right CN 3 medial rectus
    5. Neither left eye (CN 6 lateral rectus) nor right eye (CN 3 medial rectus) are able to look to the left
  3. Brainstem lesion
    1. Conjugate deviation away from the lesion
  4. Upper Midbrain lesion (or Hydrocephalus)
    1. Eyes deviated downward ("setting sun sign")
  5. Third nerve paralysis (CN 3 Palsy)
    1. Eye deviated downward and outward
  6. Fourth nerve paralysis (CN 4 palsy)
    1. Eye deviated upward (esp. on straight ahead and when adducted, looking medially)
  7. Sixth nerve paralysis (CN 6 Palsy)
    1. Eye deviated medially, when attempting lateral gaze
  8. Medial Longitudinal Fasciculus Syndrome (Internuclear Ophthalmoplegia)
    1. On lateral gaze, Cranial Nerve 6 abducts the ipsilateral eye
      1. To maintain Conjugate Gaze, a signal is passed via MLF to the contralateral eye's CN 3
        1. Opposite eye then adducts (moves medially) in parallel with the abducting eye
    2. With a MLF lesion, the adducting eye via CN 3 fails to adduct
      1. In response, the abducting eye (via CN 6) demonstrates Nystagmus
      2. Eyes able to converge normally
      3. Bilateral Medial Longitudinal Fasciculus lesions suggests Multiple Sclerosis

III. References

  1. Goldberg (2014) Clinical Neuroanatomy, Medmaster, p. 40-53

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