Anatomy and Movements of Extraocular Muscles

Anatomy

• There are six extraocular muscles (EOMs) in each eye:
  1. Lateral rectus
  2. Medial rectus
  3. Superior rectus
  4. Inferior rectus
  5. Superior oblique
  6. Inferior oblique
• EOMs are skeletal muscles that surround the eyeball
• They are responsible for moving the eyeball in its socket

Movements

• EOMs work together to produce six cardinal movements:
  1. Elevation (upward movement)
  2. Depression (downward movement)
  3. Adduction (inward movement)
  4. Abduction (outward movement)
  5. Intorsion (inward rotation)
  6. Extorsion (outward rotation)
• Each EOM has a specific action:
  • Lateral rectus: abduction
  • Medial rectus: adduction
  • Superior rectus: elevation and intorsion
  • Inferior rectus: depression and extorsion
  • Superior oblique: depression and extorsion
  • Inferior oblique: elevation and extorsion

Functions

• EOMs are responsible for:
  • Moving the eyeball to focus on objects
  • Maintaining binocular vision
  • Tracking moving objects
  • Stabilizing the gaze
  • Coordinating with other muscles to maintain posture and balance

Innervation

• EOMs are innervated by three cranial nerves:
  1. Oculomotor nerve (III): innervates superior rectus, inferior rectus, medial rectus, and inferior oblique
  2. Trochlear nerve (IV): innervates superior oblique
  3. Abducens nerve (VI): innervates lateral rectus
• Each cranial nerve has a specific function:
  • Oculomotor nerve: controls most EOMs and pupil constriction
  • Trochlear nerve: controls superior oblique
  • Abducens nerve: controls lateral rectus

Dysfunction

• EOM dysfunction can lead to:
  • Strabismus (crossed eyes)
  • Diplopia (double vision)
  • Ocular motility disorders
  • Eye movement disorders
  • Vision problems
• Causes of EOM dysfunction include:
  • Neurological disorders (e.g. stroke, Parkinson's disease)
  • Muscle imbalance or weakness
  • Injury or trauma
  • Congenital defects
  • Aging

Anatomy of Extraocular Muscles (EOMs)

• Six EOMs in each eye: lateral rectus, medial rectus, superior rectus, inferior rectus, superior oblique, and inferior oblique
• EOMs are skeletal muscles surrounding the eyeball, responsible for moving the eyeball in its socket

Movements of EOMs

• Six cardinal movements: elevation, depression, adduction, abduction, intorsion, and extorsion
• Each EOM has a specific action:
  • Lateral rectus: abduction
  • Medial rectus: adduction
  • Superior rectus: elevation and intorsion
  • Inferior rectus: depression and extorsion
  • Superior oblique: depression and extorsion
  • Inferior oblique: elevation and extorsion

Functions of EOMs

• Moving the eyeball to focus on objects
• Maintaining binocular vision
• Tracking moving objects
• Stabilizing the gaze
• Coordinating with other muscles to maintain posture and balance

Innervation of EOMs

• Three cranial nerves innervate EOMs: oculomotor nerve (III), trochlear nerve (IV), and abducens nerve (VI)
• Oculomotor nerve innervates superior rectus, inferior rectus, medial rectus, and inferior oblique
• Trochlear nerve innervates superior oblique
• Abducens nerve innervates lateral rectus
• Each cranial nerve has a specific function:
  • Oculomotor nerve: controls most EOMs and pupil constriction
  • Trochlear nerve: controls superior oblique
  • Abducens nerve: controls lateral rectus

Dysfunction of EOMs

• Can lead to: strabismus, diplopia, ocular motility disorders, eye movement disorders, and vision problems
• Causes of EOM dysfunction include:
  • Neurological disorders (e.g., stroke, Parkinson's disease)
  • Muscle imbalance or weakness
  • Injury or trauma
  • Congenital defects
  • Aging

Movements

• Eye movements occur in three dimensions: horizontal, vertical, and rotational
• Horizontal movements controlled by lateral rectus (abduction) and medial rectus (adduction)
• Vertical movements controlled by superior rectus (elevation) and inferior rectus (depression)
• Rotational movements controlled by superior oblique (intorsion) and inferior oblique (extorsion)

Anatomy

• Six extraocular muscles (EOMs) originate from the annulus of Zinn, a fibrous ring surrounding the optic nerve
• EOMs classified into two groups: recti muscles (4) and oblique muscles (2)
• Recti muscles are straight and parallel to the orbital axis
• Oblique muscles are at an angle to the orbital axis

Functions

• EOMs work together to move the eye in its socket, rotate the eye to focus on a target, and maintain binocular vision
• EOMs stabilize the gaze during head movements
• EOMs responsible for conjugate gaze (eyes move together) and vergence movements (eyes move inward or outward)

Dysfunction

• Common disorders affecting EOMs: strabismus, esotropia, exotropia, hypertropia, and convergence insufficiency
• Other conditions affecting EOMs: Graves' disease, myasthenia gravis

Innervation

• EOMs innervated by three cranial nerves: oculomotor nerve (CN III), trochlear nerve (CN IV), and abducens nerve (CN VI)
• Cranial nerves innervate specific EOMs: medial rectus, inferior rectus, inferior oblique, superior rectus, superior oblique, and lateral rectus