SGW - eye

Question 1

where is aqueous humour produced?

Answer 1

by ciliary body (ciliary processes) in the posterior chamber of the eye

Question 2

where is the posterior chamber of the eye?

Answer 2

between the iris and the lens

Question 3

where is the anterior chamber of the eye?

Answer 3

between the iris and the cornea

Question 4

what connects the ciliary body to the lens?

Answer 4

suspensory ligaments

Question 5

what is the function of aqueous humour?

Answer 5

it bathes the lens (supplying nutrients) (P. chamber) and circulates through the pupil (aperture between iris) into the anterior chamber, bathing the inner surface of the cornea (supply nutrients)

Question 6

where does aqueous humour drain?

Answer 6

through the trabeculae meshwork –> canal of Schlemm in the irido-corneal angle

Question 7

what is the irido-corneal angle?

Answer 7

angle between iris and cornea

Question 8

why is a circulation of aqueous essential?

Answer 8

there is constant supply, drainage and therefore circulation of aqueous humour is required from posterior (lens) to anterior (cornea) chamber

Question 9

how can drainage of aqueous humour be impeded?

Answer 9

if there is blockage in the trabecular meshwork (open angle glaucoma)
OR
if the iris is pushed forward blocking the irido-corneal angle (closed angle glaucoma)

Question 10

what is closed angle glaucoma?

Answer 10

medical emergency

lens compressed against iris causing COMPLETE blockage of trabeculae meshwork - cause blindness

Question 11

what are complications of impeded aqueous humour drainage?

Answer 11

The eye continues to make fluid in the ciliary body and therefore, the pressure in the eye starts to rise
a high pressure in the eye causes optic nerve damage Vision loss in open angle glaucoma starts with the far peripheral vision and is painless

Question 12

how do you treat glaucoma?

Answer 12

diuretics
muscarinic agonist (increase drainage by increasing space between irido-corneal angle?)

Question 13

why is it not possible to lose a contact lens behind the eye?

Answer 13

conjunctival membrane reflects off the sclera to line the inner surfaces of eyelid, can’t go beyond margin of conjunctival membrane
(conjunctival membrane: from limbus - angle between cornea and sclera, fibrous outer layer)

Question 14

when looking at the image of the eye, where is the optic disc, macula and blood vessels?

Answer 14

optic disc most medial
macula (fovea in centre - highest CONE cells - visual acuity) in centre
retinal blood vessels lateral
(looking at patient face on - opposite of your eye)

Question 15

what is papilloedema?

Answer 15

swelling of optic disc secondary to raised intra-cranial pressure e.g. extra-dural / subdural haemorrhage / brain tumour - usually bilateral

Question 16

whee is CSF found?

Answer 16

in subarachnoid space (between arachnoid and pia mater)

Question 17

what happens if there is an increased pressure within the brain?

Answer 17

there will be increased pressure within the CSF

pressure transmitted to optic nerve, compressing it

Question 18

what does compression of optic nerve from raised ICP lead to?

Answer 18

stems axoplasmic flow (transport of cell organelles to and from neuron’s cell body) - affects transmission of AP
causing nerve to swell - swelling at optic disc (where optic nerve + ophthalmic artery enters orbit)

Question 19

when is swelling of optic disc visible?

Answer 19

on fundoscopy

Question 20

how does optic disc appear on fundoscopy during papilloedema?

Answer 20

optic disc appears swollen, margins blurred

with increasing severity the entire nerve head may appear elevated with the borders completely obscured

Question 21

what is a cause of optic disc swelling that is not papilloedema?

Answer 21

optic neuritis (inflammation of optic nerve) can cause optic disc to swell

Question 22

what causes cupping of the optic disc?

Answer 22

seen in raised intra-ocular pressure (increased pressure INSIDE the globe of the eye e.g. glaucoma - treat with M3 agonist)

Question 23

what is the cup of the eye?

Answer 23

the central depression in the normal healthy optic disc

usually 1/3rd diameter of the whole disc (think of hole in doughnut)

Question 24

what is optic disc ‘cupping’?

Answer 24

increased diameter of the cup (cup to disc ratio no longer 1/3rd)

Question 25

how does appearance of optic disc cupping differ from papilloedema?

Answer 25

cupping:
margins are still well defined
optic disc does not appear swollen
(just a large white hole in the middle of optic disc)

Question 26

what is a quick way of defining difference between optic cupping and papilloedema?

Answer 26

pressure in FRONT of optic nerve = optic cupping

pressure from BEHIND optic nerve = papillaoedema

Question 27

what are the 3 components of the accommodation reflex?

Answer 27

convergence
pupillary constriction
suspensory ligaments relax

Question 28

why is convergence required in accommodation reflex?

Answer 28

to keep the object centred on the fovea part of the retina (resolution is highest - visual acuity) to prevent diplopia

Question 29

why is pupillary constriction required in accommodation reflex?

Answer 29

restrict diverging rays from the close object
diverging rays cannot be bent enough by the periphery of the lens to make them fall on fovea
(so narrow the aperture to only light which can fall on the fovea)

Question 30

why is relaxation of suspensory ligaments required in accommodation reflex?

Answer 30

gives ‘fat lens’ - bend light –> fovea
increases refractive index (increase power to bend light) by changing shape of lens, so light passing through lens would converge on FOVEA
(contraction of ciliary muscle = relaxation of suspensory ligaments)
suspensory ligaments contract for far vision (thin lens)

Question 31

what is presbyopia?

Answer 31

when eyes age - lens become less elastic, loosing focusing power
becomes more difficult for stiff lens to change its shape (more round) when trying to focus on near-objects
(difficult for ciliary muscles to contract into fat shaped lens, loose elastic to ‘ping’ back)

Question 32

outline direct and consensual light reflexes using the left eye as an example

Answer 32

light in left pupil –> sensory afferent from left retina (CN II optic) –> brainstem (pre-tectal nucleus) –> EDW nucleus (L+R) –> parasympathetic from EDW (ciliary ganglion) –> hitch-hike CN III (L+R) oculomotor –> pass via ciliary ganglion –> sphincter pupillae (parasympathetic) –> left (direct), right (consensual)

L+R post brainstem (so from edinger-westphal nucleus)

Question 33

what is conjunctivitis? how does it present?

Answer 33

inflammation of conjunctiva:
watery, pink eye
discomfort, but not painful
normal vision + pupillary reflexes

Question 34

what happens during conjunctiva?

Answer 34

conjunctiva normally transparent - see sclera (white of eye)
blood vessels in conjunctiva inflamed and dilate - become visible
makes eye appear pink / red

Question 35

what normally causes conjunctiva?

Answer 35

usually due to viral infection - very contagious

Question 36

why is the cornea not affected in conjunctiva?

Answer 36

conjunctiva ends at limbus (junction between cornea and sclera) - conjunctiva doesn’t overlie cornea

Question 37

what is a meibomian cyst? cause? location?

Answer 37

chalazion
blocked tarsal (meibomian) gland (meibomian normally secretes an oily material - readily form cystic swelling if DRAINAGE is blocked)
lies posterior to eyelids (within tarsal plates) - appears higher up from eye

Question 38

what is a stye? cause? location?

Answer 38

external hordeolum

infection of the sebaceous gland situated at BASE of EYELASH (LASH FOLLICLE)

Question 39

difference between meibomian cyst and stye from looking at patient?

Answer 39

stye - in line of eyelash

meibomian cyst - posterior to eyelid (blocked drainage)