Extrinsic Muscles of the Eye

Question 1

What are the 6 extrinsic muscles of the eye?

Answer 1

Superior oblique
Inferior oblique
Medial rectus
Lateral rectus
Superior rectus
Inferior rectus

Question 2

What eye actions does the superior oblique muscle mediate and which cranial nerve is it innervated by?

Answer 2

Depression, abduction, medial rotation of eyeball (primary, secondary, tertiary actions)
- Innervated by CN IV, trochlear nerve

Question 3

What eye actions does the inferior oblique muscle mediate and which cranial nerve is it innervated by?

Answer 3

Elevation, abduction, lateral rotation of the eyeball
(primary, secondary, tertiary actions)
- Innervated by CN III, oculomotor nerve

Question 4

What eye actions does the medial rectus muscle mediate and which cranial nerve is it innervated by?

Answer 4

Adduction

- innervated by CN III, oculomotor nerve

Question 5

What eye actions does the lateral rectus muscle mediate and which cranial nerve is it innervated by?

Answer 5

Abduction

- innervated by CN VI, abducens nerve

Question 6

What eye actions does the superior rectus muscle mediate and which cranial nerve is it innervated by?

Answer 6

Elevation, adduction, medial rotation of the eyeball

- innervated by CN III, oculomotor nerve

Question 7

What eye actions does the inferior oblique muscle mediate and which cranial nerve is it innervated by?

Answer 7

Depression, adduction, lateral rotation of the eyeball

- innervated by CN III, oculomotor nerve

Question 8

What is the process of the H-test of the extrinsic eye muscles?

Answer 8

1) Make sure to perform the test about 30-40cm in front of the patient’s face
2) Ask patient to keep their eye still, cover one eye and follow your finger with the other eye
3) Begin in the middle, move your finger fully to one side to abduct their eye, and move up, down, then back to the middle
4) Repeat step 3 but on the other side (adduction)
5) The whole process should result in you drawing an imaginary H in front of the patient
6) Repeat this with the patient’s other eye, with the just-rested eye covered

Question 9

What is significant about abnormalities in the H test?

Answer 9

Since the eye has multiple muscles able to perform the same action, moving the eye to the side traps these additional muscles and isolates the desired muscles. If the desired muscle is ineffective or there is nerve damage, whichever ranges of motion are impaired can be used to determine which nerve/muscle has been damaged and to what extent.