Eye & Orbit

Question 1

what passes through the inferior orbital fissure

Answer 1

inferior ophthalmic vein, infraorbital vein/artery/nerve

Question 2

where is the optic chiasm in relation to the pituitary gland

Answer 2

superior and anterior to the pituitary

Question 3

if there is injury affecting the optic nerve on one side

Answer 3

sight to that eye is lost, other eye works fine

Question 4

if there is an issue with the optic chiasm

Answer 4

fibres cross over here so lateral side of each visual field is lost if information can no longer pass across the chiasm and we end up with tunnel vision

Question 5

if there is a lesion in the optic tract on LHS

Answer 5

parts of visual field supplied by this tract will not work i.e. medial side on affected side and lateral side on RHS and this is another form hemianopia

Question 6

action of orbicularis oculi

Answer 6

palpebral part - blinking reflex (involuntary)
orbital part - scrunching of eye (voluntary)

Question 7

where is the lacrimal glad found in the orbit

Answer 7

upper lateral corner

Question 8

drainage of tears

Answer 8

tears drain via puncta to canaliculi to lacrimal sac to nasolacrimal duct and then to inferior nasal meatus

Question 9

parasympathetic supply of the lacrimal gland

Answer 9

• preganglionic parasympathetic fibres from facial nerve CN VII intermediate nerve
• travel in greater petrosal nerve & nerve of pterygoid canal
• arrive in pterygopalatine ganglion
• postganglionic parasympathetic fibres hitch-hike to zygomatic branch of CN V2 and then join the lacrimal nerve (branch of CN V1) to reach the lacrimal gland

Question 10

name the 7 extra ocular muscles

Answer 10

4 rectus muscles - superior, inferior, middle, lateral
2 obliques - superior, inferior
levator palpebrae superioris

Question 11

which extraocular muscles are not innervated by CN III

Answer 11

SO4 and LR6 i.e. superior oblique = CN IV and lateral rectus = CN VI

Question 12

levator palpebrae superioris

Answer 12

found at very top of eyeball, responsible for superior eyelid movement, CN III

Question 13

superior oblique

Answer 13

slightly medial to LPS & superior rectus, depresses and abducts eyeball (down and out), CN IV

Question 14

inferior oblique

Answer 14

at bottom of eyeball, elevates and abducts (up and out), CN III

Question 15

superior rectus

Answer 15

directly below LPS so sometimes difficult to distinguish between the two, elevates and adducts (up and in), CN III

Question 16

middle rectus

Answer 16

on side of eyeball towards nose, adducts (in), CN III

Question 17

lateral rectus

Answer 17

on side of eyeball towards exterior skull, abducts (out), CN VI

Question 18

inferior rectus

Answer 18

very bottom of eyeball, depresses and adducts (down and in), CN III

Question 19

injury of CN III can lead to paralysis of

Answer 19

superior/middle/inferior rectus, inferior oblique and levator palpebrae superioris

Question 20

effect on eye of injury to CN III

Answer 20

removes parasympathetic pupil constriction leading to dilated pupil (mydriasis) with ptosis (complete loss of levator palpebrae superioris) so eye is turned downwards and inwards as superior oblique and lateral rectus are still intact

Question 21

describe the layers of the eye

Answer 21

sclera = outermost fibrous layer
choroid = vascular layer
retina = innermost layer

Question 22

to see far away

Answer 22

ciliary muscles relaxed, suspensory ligaments tense, lens is thin for distance

Question 23

to see close up

Answer 23

ciliary muscles tense, suspensory ligaments slack, lens is thick and rounded for close up

Question 24

dilator pupillae

Answer 24

under sympathetic control (for dim light, dilated pupil)

Question 25

sphincter pupillae

Answer 25

under parasympathetic control (for bright light, constricted pupil)