SGW - eye Flashcards
where is aqueous humour produced?
by ciliary body (ciliary processes) in the posterior chamber of the eye
where is the posterior chamber of the eye?
between the iris and the lens
where is the anterior chamber of the eye?
between the iris and the cornea
what connects the ciliary body to the lens?
suspensory ligaments
what is the function of aqueous humour?
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)
where does aqueous humour drain?
through the trabeculae meshwork –> canal of Schlemm in the irido-corneal angle
what is the irido-corneal angle?
angle between iris and cornea
why is a circulation of aqueous essential?
there is constant supply, drainage and therefore circulation of aqueous humour is required from posterior (lens) to anterior (cornea) chamber
how can drainage of aqueous humour be impeded?
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)
what is closed angle glaucoma?
medical emergency
lens compressed against iris causing COMPLETE blockage of trabeculae meshwork - cause blindness
what are complications of impeded aqueous humour drainage?
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
how do you treat glaucoma?
diuretics muscarinic agonist (increase drainage by increasing space between irido-corneal angle?)
why is it not possible to lose a contact lens behind the eye?
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)
when looking at the image of the eye, where is the optic disc, macula and blood vessels?
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)
what is papilloedema?
swelling of optic disc secondary to raised intra-cranial pressure e.g. extra-dural / subdural haemorrhage / brain tumour - usually bilateral
whee is CSF found?
in subarachnoid space (between arachnoid and pia mater)
what happens if there is an increased pressure within the brain?
there will be increased pressure within the CSF
pressure transmitted to optic nerve, compressing it
what does compression of optic nerve from raised ICP lead to?
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)
when is swelling of optic disc visible?
on fundoscopy
how does optic disc appear on fundoscopy during papilloedema?
optic disc appears swollen, margins blurred
with increasing severity the entire nerve head may appear elevated with the borders completely obscured
what is a cause of optic disc swelling that is not papilloedema?
optic neuritis (inflammation of optic nerve) can cause optic disc to swell
what causes cupping of the optic disc?
seen in raised intra-ocular pressure (increased pressure INSIDE the globe of the eye e.g. glaucoma - treat with M3 agonist)
what is the cup of the eye?
the central depression in the normal healthy optic disc
usually 1/3rd diameter of the whole disc (think of hole in doughnut)
what is optic disc ‘cupping’?
increased diameter of the cup (cup to disc ratio no longer 1/3rd)
how does appearance of optic disc cupping differ from papilloedema?
cupping:
margins are still well defined
optic disc does not appear swollen
(just a large white hole in the middle of optic disc)
what is a quick way of defining difference between optic cupping and papilloedema?
pressure in FRONT of optic nerve = optic cupping
pressure from BEHIND optic nerve = papillaoedema
what are the 3 components of the accommodation reflex?
convergence
pupillary constriction
suspensory ligaments relax
why is convergence required in accommodation reflex?
to keep the object centred on the fovea part of the retina (resolution is highest - visual acuity) to prevent diplopia
why is pupillary constriction required in accommodation reflex?
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)
why is relaxation of suspensory ligaments required in accommodation reflex?
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)
what is presbyopia?
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)
outline direct and consensual light reflexes using the left eye as an example
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)
what is conjunctivitis? how does it present?
inflammation of conjunctiva:
watery, pink eye
discomfort, but not painful
normal vision + pupillary reflexes
what happens during conjunctiva?
conjunctiva normally transparent - see sclera (white of eye)
blood vessels in conjunctiva inflamed and dilate - become visible
makes eye appear pink / red
what normally causes conjunctiva?
usually due to viral infection - very contagious
why is the cornea not affected in conjunctiva?
conjunctiva ends at limbus (junction between cornea and sclera) - conjunctiva doesn’t overlie cornea
what is a meibomian cyst? cause? location?
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
what is a stye? cause? location?
external hordeolum
infection of the sebaceous gland situated at BASE of EYELASH (LASH FOLLICLE)
difference between meibomian cyst and stye from looking at patient?
stye - in line of eyelash
meibomian cyst - posterior to eyelid (blocked drainage)
