Lecture 17 - Extra-ocular muscles

Question 1

Extrinsic muscles

Answer 1

Muscles of the eyelid

• Obicularis oculi (CN VII)
• Levator palpebrae superioris (CN III)
• Superior tarsal muscles - sympathetics

Extra-ocular muscles:

• Superior rectalis
• Inferior rectalis
• Lateral rectalis - CN VI
• Medial rectalis
• Superior oblique - CN IV
• Inferior oblique

Question 2

Intrinsic muscles

Answer 2

Muscles of the iris:

• Sphincter pupillae - parasympathetics
• Dilator pupillae - sympathetics

Ciliary muscles - controls thickness of lens

Question 3

Where do the rectalis muscles originate from

Answer 3

Tendinous ring

Question 4

Where do the oblique muscles originate from

Answer 4

Bony wall of orbit

Question 5

Innervation of extra-ocular muscles

Answer 5

CN III:

• Superior rectalis
• Inferior rectalis
• Medial rectalis
• Inferior oblique
• Superior oblique - CN IV
• Lateral rectalis - CN VI

Question 6

Primary resting gaze

Answer 6

• Equal and opposite pull of all the extra-ocular muscles
• Aligned visual axis - no diplopia
• Images reaaching the cortex is fused and seen as one therefore binocular vision - 3D depth perception

Question 7

How to change position of gaze

Answer 7

Greater pull is exerted by specific extra-ocular muscles with simultaneous relaxation of antagonist

Requires aligned visual axes via conjugate gaze to prevent diplopia

Question 8

Medial rectus

Answer 8

Origin: tendinous ring in apex of orbit
Insertion: Medial eyeball
Action: Adduction
Innervation: CN III

Question 9

Lateral rectus

Answer 9

Origin: tendinous ring in apex of orbit
Insertion: Lateral eyeball
Action: abduction
Innervation: Abducens nerve

Question 10

Superior rectus

Answer 10

Origin: tendinous ring in apex of orbit

Insertion - superior anterolateral surface of eyeball obliquely

Action: Elevate
Slight adduction
Slight internally rotates

Innervation: CN III

Question 11

Inferior rectus

Answer 11

Origin: tendinous ring in apex of orbit

Insertion: Anteroinferior surface of eyeball obliquely

Action: Depress
Slightly adduct
Slight external rotation

Question 12

Superior oblique

Answer 12

Origin: Lateral walls of orbit in apex of orbit through trochlear

Insertion: Superoposterior aspect of globe

Action:
Internally rotate
Depress
Slightly abduct

Innervation: CN IV

Question 13

Inferior oblique

Answer 13

Origin: anteromedial surface of floor of orbit

Insertion: inferoposterior surface of globe

Action:
Elevate
Externally rotate
Slightly abduct

Innervation: CN III

Question 14

Strabismus

Answer 14

Squint - resting position of eyeball deviates due to lack of antagonising

Question 15

CN VI lesion

Answer 15

Eye is adducted in resting gaze

Lateral rectus weakness: can’t abduct

Question 16

CN IV lesion

Answer 16

Eye is held in up and in position at rest:

Elevated
Externally rotated
Adducted

Superior oblique affected therefore cannot:
Depress
Internally rotate
Abduct

Compensate for slight extortion by tilting head

Worsening diplopia when looking down and in - walking downstairs and reading

Question 17

Clinical examination of eye movements

Answer 17

Isolate action of each muscle to test therefore ‘H’ with eyes

Test CN III, IV and VI

Question 18

Midline elevation

Answer 18

IO: elevates/externally rotates/abducts

SR: Elevates/ internally rotates adducts

Question 19

Midline depression

Answer 19

SO: Depress/ internally rotate/ abduct

IR: Depress/ externally rotate/adduct

Question 20

Lateral stating position

Answer 20

Elevation by superior rectus

Depression by inferior rectus rectus

Question 21

Medial starting position

Answer 21

Elevation by inferior oblique

Depression by superior oblique

Question 22

CN III lesion

Answer 22

Complete ptosis - LPS weakness

Down and out position due to weakness of:

• Superior rectus
• Inferior rectus
• Medial rectus - unopposed lateral rectus
• Inferior oblique - Unopposed superior oblique

Pupil dilated - sphincter pupillae weakness (in vascular lesion spared)