II. Causes
- See Extraocular Movement
-
Cerebrovascular Accident affecting Brodmann's area 8
- Conjugate deviation toward the side of the lesion (Eyes look toward the lesion)
- For example, eyes look to the right-sided CVA lesion as they are unable to look to the contralateral side
- Innervation of left-sided CN 6 nucleus is interrupted, as is Lateral Gaze Center and Medial Longitudinal Fasciculus
- Loss of Conjugate Gaze with interrupted Medial Longitudinal Fasciculus
- No signals passed to ipsilateral, right CN 3 medial rectus
- Neither left eye (CN 6 lateral rectus) nor right eye (CN 3 medial rectus) are able to look to the left
-
Brainstem lesion
- Conjugate deviation away from the lesion
- Upper Midbrain lesion (or Hydrocephalus)
- Eyes deviated downward ("setting sun sign")
- Third nerve paralysis (CN 3 Palsy)
- Eye deviated downward and outward
- Fourth nerve paralysis (CN 4 palsy)
- Eye deviated upward (esp. on straight ahead and when adducted, looking medially)
- Sixth nerve paralysis (CN 6 Palsy)
- Eye deviated medially, when attempting lateral gaze
-
Medial Longitudinal Fasciculus Syndrome (Internuclear Ophthalmoplegia)
- On lateral gaze, Cranial Nerve 6 abducts the ipsilateral eye
- To maintain Conjugate Gaze, a signal is passed via MLF to the contralateral eye's CN 3
- Opposite eye then adducts (moves medially) in parallel with the abducting eye
- To maintain Conjugate Gaze, a signal is passed via MLF to the contralateral eye's CN 3
- With a MLF lesion, the adducting eye via CN 3 fails to adduct
- In response, the abducting eye (via CN 6) demonstrates Nystagmus
- Eyes able to converge normally
- Bilateral Medial Longitudinal Fasciculus lesions suggests Multiple Sclerosis
- On lateral gaze, Cranial Nerve 6 abducts the ipsilateral eye
III. References
- Goldberg (2014) Clinical Neuroanatomy, Medmaster, p. 40-53