Extraocular Movement

Aka: Extraocular Movement, Oculomotor Nerve Structure, Conjugate Gaze, Pontine Paramedian Reticular Formation, Lateral Gaze Center, Paraabducens Nucleus, Medial Longitudinal Fasciculus, Ophthalmoplegia, Ocular Motility, Ocular Motility Disorder, Superior Rectus Muscle, Inferior Rectus Muscle, Lateral Rectus Muscle, Medial Rectus Muscle, Superior Oblique Muscle, Inferior Oblique Muscle, Orbitalis Muscle, Muller's Muscle, Levator Palpebrae Superioris Muscle, Orbicularis Oculi Muscle

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II. Definitions

  1. Conjugate Gaze
    1. Movement of both eyes in the same direction at the same time
  2. Ophthalmoplegia
    1. Weakness or paralysis of one or more Extraocular Movement Muscles
    2. Results from either a Muscle disoder or nerve palsy

III. Background

  1. Three different nerves rotate the eye's axis (line of sight)
    1. Oculomotor Nerve (CN 3)
    2. Trochlear Nerve (CN 4)
    3. Abducens Nerve (CN 6)
  2. Oculomotor Nerve (CN 3) innervates 3 of the 5 eye Muscles
    1. Allows the eye to look up, down and medially
    2. CN 3 Palsy results in the eye is oriented 'down and out' (functionality of the 2 remaining nerves)
  3. Trochlear Nerve (CN 4) innervates the Superior Oblique Muscle
    1. Pulley system (trochlea) to rotate the eye downward and laterally
  4. Abducens Nerve (CN 6) innervates the Lateral Rectus Muscle
    1. Rotates the eye laterally
  5. Conjugate Gaze (alignment of both eyes) is the most complex Extraocular Movement
    1. Requires one eye to look laterally (CN 6) while the other eye looks medially (CN 3)
    2. Synchrony requires coordination from several centers
      1. Contralateral cerebral cortex (Brodmann Areas 17,18,19 and 8)
      2. Lateral Gaze Center (Pontine Paramedian Reticular Formation or PPRF)
      3. Signals to ipsilateral CN 6
      4. Signals to contralateral CN 3 (via Medial Longitudinal Fasciculus)

IV. Anatomy: Innervation

  1. Cerebral Cortex
    1. Voluntary Conjugate Gaze (Brodmann's Area 8)
    2. Involuntary Conjugate Gaze (Areas 17-19)
  2. Cranial Nerves
    1. CN 3 (nucleus in Midbrain)
    2. CN 4 (nucleus in Midbrain)
    3. CN 6 (nucleus in pons)
  3. Nucleii and Pathways
    1. Lateral Gaze Center (Pontine Paramedian Reticular Formation, Paraabducens Nucleus)
      1. Responsible for horizontal gaze and saccade eye movements
      2. Facilitates Conjugate Gaze by synapsing with contralateral fibers for coordinated eye movements
    2. Medial Longitudinal Fasciculus (MLF)
      1. Transmits signals between CN 3 and CN 6 to coordinate eye movements (Conjugate Gaze)
      2. Dysfunctional in Internuclear Ophthalmoplegia (e.g. Multiple Sclerosis, esp. if bilateral)
      3. Example of normal Conjugate Gaze pathway via Medial Longitudinal Fasciculus
        1. Cortical signal from voluntary gaze center directs left eye to look left
        2. Left eye CN 6 (lateral rectus) fires for the left eye to look left
        3. CN 6 signals Synapse with the Lateral Gaze Center
        4. Signals are transmitted via Medial Longitudinal Fasciculus across midline to contralateral CN 3
        5. Medial rectus directs the right eye to also look left (adduct to look medially)

V. Anatomy: Extraocular Muscles (Innervated by CN 3 with 2 exceptions)

  1. See Brainstem CVA
  2. Background
    1. All extraocular Muscles stretch from globe to nasal aspect of the orbit
    2. None of the extraocular Muscles anchor to the temporal orbit
  3. Medial Range of Motion
    1. Medial Rectus Muscle (Cranial Nerve 3)
  4. Lateral Range of Motion
    1. Lateral Rectus Muscle (Cranial Nerve 6)
  5. Upward Range of Motion
    1. Superior Rectus Muscle (Cranial Nerve 3)
    2. Inferior Oblique Muscle (Cranial Nerve 3)
      1. Deficit results in vertical Diplopia, and Head Tilt compensating for eye rotation
      2. Function depends on eye position
        1. Eye looks up (nasal position)
        2. Eye rotates (temporal position)
        3. Eye looks up and out (neutral straight ahead position)
  6. Downward Range of Motion
    1. Inferior Rectus Muscle (Cranial Nerve 3)
    2. Superior Oblique Muscle (Cranial Nerve 4, Trochlear Nerve)
      1. Pulley system (trochlea) to rotate the eye downward and laterally
      2. CN 4 Paralysis results in vertical Diplopia, and Head Tilt compensating for eye rotation
      3. Function depends on eye position
        1. Eye looks down (nasal position)
        2. Eye rotates (temporal position)
        3. Eye looks down and out (neutral straight ahead position)
  7. Other extraocular Muscles affected Eyelid position
    1. Upper Eyelid Opening
      1. Levator Palpebrae Superioris Muscle (CN 3)
        1. Defect results in significant Ptosis
      2. Muller's Muscle or Orbitalis Muscle (cervical Sympathetic Nerves)
        1. Defect results in mild Ptosis
    2. Upper Eyelid Closure
      1. Orbicularis Oculi Muscle (Cranial Nerve 7, defective in Bell's Palsy)

VI. Anatomy: Images

  1. See Neurologic Anatomy of the Eye
  2. eye_eom.png
  3. eyeOculomotorGrayBB785.gif Lewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
  4. eyeOculomotorGrayBB889.gif Lewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)

VII. Pathophysiology

  1. See Eye Deviation

VIII. References

  1. Goldberg (2014) Clinical Neuroanatomy, Medmaster, p. 40-53
  2. Netter (1997) Atlas Human Anatomy, ICON Learning, p. 114, 126

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