Topic 11 Extraocular Muscles

Question 1

what are the 9 directions of gaze?

Answer 1

1. primary position, straight ahead, eye focused at infinity

Secondary positions:

2. infraversion (both eyes looking down)
3. supraversiom (both eyes looking up)
4. dextroversion (both eyes looking right)
5. levoversion (both eyes looking left)

Tertiary positions:

6. dextrosupraverion (both eyes right up)
7. dextroinfraversion (both eyes right down)
8. levosupraversion (both eyes left up)
9. levoinfraversion (both eyes left down)

Question 2

what are the 6 monocular eye movements?

Answer 2

1. supraduction
   2.infraduction
2. adduction (nasally, inwards)
   rmb ADD IN
3. abduction (temporally, outwards)
4. excycloduction (cycle movement temporally)
5. incycloduction (cycle movement nasally)

Question 3

what are the 6 binocular eye movements for versions? (both eyes move tgt towards same direction)

Answer 3

1. dextroversion (right)
2. levoversion (left)
3. supraversion (up)
4. infraversion (down)
5. dextrocycloversion (cycle movement tw right)
6. levocycloversion (cycle movement tw left)

Question 4

what are the 6 binocular eye movements for vergence? (both eyes move in opposite direction)

Answer 4

1. convergence (nasal)
2. divergence (temporal)
3. positive vertical divergence (right up, left down)
4. negative vertical divergence (left up right down)
5. incyclovergence (cycle movement nasally both eyes)
6. excyclovergence (cycle movement temporally both eyes)

Question 5

what is herings law of equal innervation?

Answer 5

• equal innervation to yoke muscles

- one muscle from each eye that work together in the same direction are yoke muscles (e.g RLR & LMR are yoke muscles)

Question 6

what is Sherrington’s law of reciprocal innervation

Answer 6

• reciprocal innervation to antagonistic muscles
• 2 muscles of the same eye that work in opposite directions are antagonistic muscles
• when a muscle is stimulated, its antagonist is inhibited (eg RMR & RLR are antagonistic muscles)

Question 7

how to rmb actions of eom? OAAB SAI IAE RAD

Answer 7

OAA ‘obliques are abductors’ (both superior & inferior oblique muscles are abductors)

SAI ‘superiors are intorters’ (superior rectus and superior oblique are intorters) & ‘inferiors are extorters’ (inferior rectus & inferior oblique are extorters)

RAD ‘recti are adductors (superior rectus, medial rectus & inferior rectus are adductors) EXCEPT lateral rectus’ (which is an abductor)

Question 8

LOOK AT YOKE MUSCLE ILLUST

Answer 8

oga

Question 9

what is the blood supply of the EOM?

Answer 9

• Muscular branches of the ophthalmic artery.
• The inferior EOM (IO,IR) are also supplied by the infraorbital artery.

SR AND SO also supplied by supraorbital artery

Question 10

what is the innervation of the EOM? (LR6 SO4)3

Answer 10

All muscles are innervated by CN3 (Oculomotor nerve)

EXCEPT Lateral rectus is innervated by CN6 (Abducen nerve)

AND Superior oblique is innervated by CN4 (Trochlear nerve)