The extraocular muscles are the six muscles that control the movements of the eyes. For reasons we don't fully understand, these muscles can be particularly affected by myasthenia. Usually, our eye movements are synchronised but when these muscles become fatigued, sometimes they don't move in accord with each other leading to double vision. Details of these muscles are shown below:

Medial Rectus (MR)

  • This moves the eye inwards, towards the nose (adduction)

Lateral Rectus (LR)

  • Moves the eye outwards, away from the nose (abduction)

Superior Rectus (SR)

  • Moves the eye Upwards (Elevation)
  • Rotates the top of the eye towards the nose (intorsion)
  • Moves the eye inward (adduction)

Inferior Rectus (IR)

  • Moves the eye downwards (depression)
  • Rotates the top of the eye away from the nose (extorsion)
  • Moves the eye inward (adduction)

Superior Oblique (SO)

  • Rotates the top of the eye towards the nose (intorsion)
  • Moves the eye downwards (depression)
  • Moves the eye outwards (abduction)

Inferior Oblique (IR)

  • Rotates the top of the eye away from the nose (extorsion)
  • Moves the eye upwards (elevation)
  • Moves the eye outwards (abduction)

There are also small muscles that control the eyelids, when they become fatigued drooping eyelids (ptosis) can occur.