Internuclear ophthalmoplegia

Internuclear ophthalmoplegia

• Horizontal conjugate gaze refers to the normal ability of both eyes to move together in the same horizontal direction (either left or right)
• This requires precise coordination between the eye that abducts and the eye that adducts so that the visual axes remain aligned.
• The MLF is a paired white-matter tract located in the paramedian brainstem (pons and midbrain)
  The medial longitudinal fasciculus is located in the paramedian area of the midbrain and pons
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  Importance: 57
  . It coordinates horizontal eye movements by connecting:
  • the abducens (VI) nucleus on one side
  • with the contralateral oculomotor (III) nucleus
• This linkage allows the abducting eye and the adducting eye to move synchronously during horizontal gaze.

• During horizontal gaze, the abducens nucleus activates:
  • the ipsilateral lateral rectus (via CN VI)
  • the contralateral medial rectus (via the MLF to CN III)
• A lesion of the MLF interrupts this signal → the eyes can no longer move together horizontally.

• Impaired adduction of the eye on the same side as the lesion
• Horizontal nystagmus of the abducting contralateral eye
• Convergence is preserved, as this does not require the MLF

• Multiple sclerosis
  Bilateral internuclear ophthalmoplegia in younger patient --> ?multiple sclerosis
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  Importance: 66
  • commonly causes bilateral MLF lesions
  • optic neuritis by itself does not cause INO
• Brainstem stroke
  Unilateral internuclear ophthalmoplegia in older patient --> ?brainstem stroke
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  Importance: 85
  • typically causes unilateral lesions, especially in older patients