Eye muscles

Question 1

what are the two groups of ocular muscles

Answer 1

intrinsic and extrinsic

Question 2

what do intrinsic muscles do

Answer 2

control pupil diameter and help alter lens curvature to enable us to see near objects

Question 3

what do extrinsic muscles do

Answer 3

move the eye (also known as extraoccular muscles or EOMs)

Question 4

what are the 6 extrinsic muscles that move the eye and one extrinsic muscle that moves the eyelid

Answer 4

4 straight muscles called RECTI:

• medial rectus
• lateral rectus
• inferior rectus
• superior rectus

2 OBLIQUE muscles:

• superior oblique
• inferior oblique

moves eyelid
- Levator palpebrae superioris

Question 5

where do the recti muscles arise from and insert

Answer 5

the apex of the orbit from an annular fibrous ring

insert at the sclera anteriorly

Question 6

where does the superior oblique muscle arise from and insert

Answer 6

the roof of the orbit posteriorly (lesser wing of sphenoid

inserts at sclera posteriorly

Question 7

where does the inferior oblique muscle arise from and insert

Answer 7

the floor of the orbit anteriorly

inserts at sclera posteriorly

Question 8

what muscle elevates the eyelid

Answer 8

levator palpebra superioris

Question 9

what is the origin of the LPS and where does it insert

Answer 9

roof of the orbit

inserts into the upper eyelid

Question 10

what muscle closes the eyelid

Answer 10

obicularis oculi (NOT AN EOM)

Question 11

what nerve supplies the superior oblique

Answer 11

trochlear (IV)

Question 12

what nerve supplies the lateral rectus

Answer 12

abducens (VI)

causes abduction of eye

Question 13

what nerve supplies all other extrinsic eye muscles

Answer 13

occulomotor (III)

Question 14

What does RADSIN stand for

Answer 14

Recti ADduct

Superiors INtort

Question 15

What are the actions on the eye of the medial recuts

Answer 15

adduction

Question 16

What are the actions on the eye of the lateral rectus

Answer 16

abduction

Question 17

What are the actions on the eye of the superior rectus

Answer 17

1. elevation
2. adduction
3. intorsion

Question 18

What are the actions on the eye of the inferior rectus

Answer 18

1. depression
2. adduction
3. extorison

Question 19

What are the actions on the eye of the superior obliques

Answer 19

1. introrsion
2. depression
3. abduction

Question 20

What are the actions on the eye of the inferior obliques

Answer 20

1. extorsion
2. elevation
3. abduction

Question 21

what is strabismus

Answer 21

squint - misalignment of the eyes

Question 22

what are the two types of squint

Answer 22

1. esotropia (manifest convergent squint)

2. exotropia (manifest divergent squint)

Question 23

what are the 2 functional consequences of squint

Answer 23

1. amblyopia (lazy eye) - brain suppress image of one eye leading to poor vision in that eye (no pathology)
2. diplopia (double vision) - usually occurs in squints occurring as a result of nerve palsies

Question 24

what are the three intrinsic muscles of the eye

Answer 24

1. ciliaris muscle (in ciliary body)
2. constrictor pupillae (in iria at pupillary border)
3. dilator pupillae (radially running muscle in iris)

Question 25

what innervates the ciliary muscle

Answer 25

parasympathetic oculomotor (III) nerve

Question 26

what innervates the constrictor pupillae

Answer 26

parasympathetic oculomotor (III) nerve

Question 27

what innervates the dilator papillae

Answer 27

sympathetic plexus around blood vessels

Question 28

what is the pupillary reaction to increased light

Answer 28

parasympathetic innervation = both pupils constrict

Question 29

what is the pupillary reaction to decreased light

Answer 29

sympathetic innervation = both pupils dilate

Question 30

what is the AFFERENT limb pathway of the light reflex

Answer 30

light falls on retina - impulses travel along optic nerve - optic chiasma - optic tract

fibres don’t go to the lentiform geniculate body - instead leave optic tract and go straight to midbrain (oculomotor III nucleus)

part of III nucleus is the Edinger-westphal nucleus for parasympathetic fibres -

Question 31

what is the EFFERENT limb pathway of the light reflex

Answer 31

from EWN (part of III nucleus) - preganglionic parasympathetic pass through III into orbit

parasympathetic fibres for to and synapes in ciliary ganglion

post ganglionic fibres go through short ciliary nerves to constrictor pupillae

pupillary constriction of BOTH EYES

Question 32

what are 2 examples of pupil abnormalities

Answer 32

1. pupils may be different size - anisocoria e.g. corners syndrome
2. pupils may look normal but react abnormally to light (abnormal light reflex)

Question 33

what can cause absent/abnormal pupillary reflexes

Answer 33

1. any abnormality of the afferent limb/ centre / efferent limb of the reflex
2. diseases of the retina - detachment, degeneration, dystrophy
3. diseases of the optic nerve - e.g. optic neuritis in MS
4. diseases of the III cranial nerve (efferent limb)

Question 34

what must you check for if there is a III nerve palsy due to a medical cause e.g. diabetes

Answer 34

medical cause = no damage to parasympathetic fibres

check pupillary reflex - if absent - suspect cerebral artery aneurysm = EMERGENCY

Question 35

what is anisocoria that occurs in horners syndrome

Answer 35

damage to the sympathetic innervation of the pupil - causes pupil to be unable to dilate in dark conditions

Question 36

what is the triad of eye symptoms in horners syndrome

Answer 36

anisocoria - pupils different size

ptosis - drooping of eyelid on affected side

anhidrosis - loss of sweating on the affected side

Question 37

what can cause horners syndrome

Answer 37

any disruption along sympathetic chain innervation - e.g. pancoasts tumour of the lung

(thoracolumbar outflow, sympathetic chain, cervical ganglia, postganglionic sympathetic fibres travelling with blood vessels in head and neck)