L15: ocular muscles, movements and testing

Question 1

What happens if there is misalignment of visual axes?

Answer 1

Misalignment of two visual axes image focuses on different area of each retina – brain unable to ‘fuse’ & therefore see two separate images
Diplopia (double vision) – two images seen

Question 2

Describe the extra-ocular muscles

Answer 2

Four recti & two obliques
Origin: apex of orbit (except IO, which arises from floor of orbital cavity anteriorly) & insertion: sclera
Majority innervated by CN III, except two – LR6SO4
Each muscle will have a certain pull & action on eye movement

Question 3

Describe the primary resting gaze

Answer 3

Even ‘at rest’ – constancy of activity in all extraocular muscles on the eyeball
During resting gaze their actions are balanced allowing for forward gaze
Each muscle has antagonist of its movement

Question 4

Describe action and innervation of medial rectus

Answer 4

Moves eye medially (adduction)

CN III

Question 5

Describe action and innervation of lateral rectus

Answer 5

Moves eye laterally (abduction)

CN VI

Question 6

Describe the action of superior rectus muscle

Answer 6

Inserts obliquely into superior anterolateral surface of globe
Actions (if starting from primary resting gaze):
-elevate
-slightly adducts
-slightly intorts
More powerful elevator when eye is positioned laterally

Question 7

Describe the actions of inferior rectus muscle

Answer 7

Inserts obliquely into anteroinferior surface of globe
Actions (if starting from primary resting gaze):
-depress
-slightly adducts
-slightly extorts
More powerful depressor when eye is positioned laterally

Question 8

Describe the actions of superior oblique muscle

Answer 8

Arises from apex of orbit, passes through trochlea, inserts into superior-posterior aspect of globe
Actions (if starting from primary resting gaze):
-intort
-depress
-slightly abducts
More powerful depressor when eye is positioned medially

Question 9

Describe the actions of inferior oblique muscle

Answer 9

Arises from the anteromedial surface of floor of orbit & inserts into infero-posterior aspect of globe
Actions (if starting from primary resting gaze):
Extort
Elevate
Slightly abduct
More powerful elevator when eye is positioned medially

Question 10

Describe how to test superior and inferior rectus

Answer 10

1) Bring eye laterally first
2) Look up (SR)
3) Look down (IR)

Question 11

Describe how to test superior and inferior oblique

Answer 11

1) Bring eye medially
2) Look up (IO)
3) Look down (SO)

Question 12

Describe ocular misalignment (strabismus)

Answer 12

Common in children
In adults -> ‘acquired’ due to pathology/disease involving number of different structures
Cranial nerves can be affected

Question 13

Describe CN III palsy

Answer 13

Eye is down and out – unopposed actions of LR & SO
Acquired causes split into two:
1) Vasculopathic (microvascular) lesions eg. diabetes/hypertension – pupil is spared
2) Compressive lesions (raised ICP, tumour, PCA aneurysm) – pupil involved (parasympathetic fibres wrapped around the outer surface of the nerve)

Question 14

Describe CN IV palsy

Answer 14

In resting gaze: eyeball is extorted, slightly elevated & adducted
Extortion of eyeball can be compensated by head tilt
Worsening diplopia especially looking down and medially

Question 15

Describe CN VI palsy

Answer 15

Unopposed pull of medial rectus – unable to abduct eye on affected side
Report diplopia, made worse on horizontal gaze

Question 16

Describe the corneal reflex

Answer 16

Afferent limb - ophthalmic division of trigeminal nerve

Efferent limb - facial nerve