Anatomy of Eye Movement for Assessment

Sep 13, 2024

Mindmap

Lecture on Eye Movement Anatomy for Clinical Assessment

Overview

  • Focus on anatomy related to clinical assessment of eye movements
  • Excludes visual acuity, field testing, reflexes, autonomic innervation
  • Focuses on the innervation and functions of six extraocular muscles:
    • Inferior rectus
    • Lateral rectus
    • Inferior oblique
    • Superior rectus
    • Medial rectus
    • Superior oblique

Cranial Nerve Innervation

  • Oculomotor Nerve (Cranial Nerve 3)
  • Trochlear Nerve (Cranial Nerve 4)
  • Abducens Nerve (Cranial Nerve 6)
  • Mnemonic: LR6, SO4, R3
    • Lateral rectus: CN 6
    • Superior oblique: CN 4
    • Others: CN 3

Eye Position and Muscle Alignment

  • Eye in primary position: looks straight ahead, visual axis parallel to sagittal axis
  • Deviates approximately 23 degrees nasally from bony orbit
  • Four rectus muscles aligned with bony orbit axis
  • Muscle insertions:
    • Rectus muscles: anterior to horizontal axis
    • Oblique muscles: posterior to horizontal axis

Eye Movements

  1. Elevation: looking up
  2. Depression: looking down
  3. Adduction: looking in
  4. Abduction: looking out
  5. Intorsion: rolling top of eye medially
  6. Extorsion: rolling top of eye laterally
  • Intorsion and extorsion stabilize images on the retina

Functions of Extraocular Muscles

  • Medial Rectus: Adduction
  • Lateral Rectus: Abduction
  • Superior Rectus: Elevation, adduction, intorsion
  • Inferior Rectus: Depression, adduction, extorsion
  • Inferior Oblique: Extorsion, elevation, abduction
  • Superior Oblique: Intorsion, depression, abduction

Testing Eye Movements

  • Six cardinal directions: in, up and in, down and in, out, up and out, down and out
  • Use object in large H pattern for testing each muscle

Clinical Implications and Nerve Palsies

  • Oculomotor Nerve Palsy (CN3):
    • Eye stuck "down and out" due to lateral rectus and superior oblique dominance
  • Trochlear Nerve Palsy (CN4):
    • Difficulty depressing and intorting the affected eye
    • Compensated by head tilt and chin tuck
  • Abducens Nerve Palsy (CN6):
    • Difficulty abducting affected eye
    • May compensate by turning head toward injured side

Conclusion

  • The eye movement exam tests cranial nerve functions and can indicate nerve disorders rather than mechanical issues.
  • Understanding muscle functions and innervation aids in diagnosing eye movement disorders.