8. Muscles of the eye

Question 1

which cranial n. palsy is this and what is the effect

Answer 1

• abducens n palsy
• paralysis of lateral rectus
• inability to abduct eye

Question 2

which cranial n palsy is this and what is the effect

Answer 2

• occulomotor n
• paralysis of medial, superior and inferior recti, and inferior oblique
• unopposed pull of lateral rectus and superior oblique causes ‘down and out’ position - abducted and depressed
• paralysis of LPS causes complete ptosis
• paralysis of PNS to sphincter pupillae causes pupil dilation

Question 3

which cranial n palsy is this

Answer 3

• trochlear n

Question 4

what are the functions of superior and inferior rectus

Answer 4

• both adduct eye (also have medial line of pull due to orbit apex being more medial than base)
• superior rectus: elevates eye
• inferior rectus: depresses eye

Question 5

what are the functions of medial and lateral rectus

Answer 5

• medial: adducts
• lateral: abducts

Question 6

what are the 3 functions of superior oblique

Answer 6

1. depresses eye
2. abducts eye
3. intorts eye

Question 7

what are the 3 functions of inferior oblique

Answer 7

1. elevates eye
2. abducts eye
3. extorts eye

Question 8

which muscles move the eye directly upwards or downwards

Answer 8

• upwards: superior rectus + inferior oblique (secondary actions cancel each other out to keep eye central)
• downward: inferior rectus + superior oblique (secondary actions cancel each other out to keep eye central)

Question 9

how is clinical testing of the extra occular muscles performed

Answer 9

make H shape:

• adduct eye = medial rectus
• abduct eye = lateral rectus
• elevate eye when abducted = superior rectus
• depress eye when abducted = inferior rectus
• elevate eye when adducted = inferior oblique
• depress eye when adducted = superior oblique