The eyes in health and disease Flashcards
what type of epithelium lines the cornea?
stratified squamous non-keratinised epithelium
what is the name of the basement membrane which the epithelium lies on?
bowman membrane
where does the storm of the cornea gets its nutrition from and why?
the cornea contains no blood vessels
it gets it nutrition from the aqueous humour and surrounding blood vessels
what type of fibre are found within the storm of the cornea?
regularly arranged collagen fibres
what makes the cornea transparent?
collagen fibres are regularly arranged
no blood vessels
endothelial layer has a pump which actively keeps aqueous humour out of the cornea
why does avasularity play an important role in corneal transplant?
because there are no blood vessels, there are no antigens
you don’t have to worry about antigen mismatch between donor and recipient
lesser chance of graft rejection
regarding the drainage of the AH, where does it stop?
the angle of the anterior chamber
describe the drainage of the AH?
produced in posterior chamber of anterior compartment
it is released from the ciliary body
it stops at the angle of the anterior junction
and flows out through the trabecular meshwork and then into shclemms canal
this then leads into venous circulation
what is the histological structure of the retina?
10 layers ;
1st layer = pigment epithelium (nourishes rods and cones)
2nd layer = layer of rods and cones (photosensitive layer)
9th layer = fibrous layer
what layer of the retina is the rods and cones found?
2nd layer (photosensitive layer)
what type of blood vessels is the choroid made up of?
fenestrated blood vessels
what is the blood supply of the retina?
10th layer supplied by the choroid
inner 9 layers supplied by the central retinal artery
what is the main problem which causes age related macular degeneration of the retina?
dystrophy that affects the pigment epithelial layer (1st layer) of the retina which leads to destruction of the rods and cones
this is because the pigment epthelial layer nourishes the rods and cones
what is the part of the eye which has the most acuity and why?
the fovea centralis
the part which is packed with the most rods and cones
what is the structure of the lens?
transparent
biconvex
what predisposes the lens to becoming opaque later on in life and what is this termed as?
the avascularity of the lens
this is known as cataract
what is one of the main causes of the lens becoming opaque later on in life?
UV rays which the lens absorbs to protect the cornea from damage
what muscle just lies underneath the surface of the eyelid and what action does it have? what nerve innervation does it have?
levator palpebrae superioris
elevates the eyelid
CN III
what prevents evaporation of the eyes tear film?
meibomian glands found at the tarsal plate
how long does it take before th tear film breaks up?
4 seconds
how long does it take before there is ocular discomfort ?
5 seconds
how long does it take before you take a blink?
7 seconds
how does the tear film stimulate blinking?
when the eyes are open the aqueous components of the tears begin to evaporate
eventually the oily and mutinous layer will meet
when these 2 layers meet it causes the tear film to break up which stimulates blinking
what is the nerve stimulation of secretion of tears into the conjunctival sac?
parasympathetic facial nerve CN VII
what are the 3 layers of the tear film?
inner - mucinous layer
middle - aqueous layer
outer - oily layer
what are the functions of the tear film?
keeps cornea moist and prevents drying
washes away any particulate foreign bodies
has antibodies and lysozymes to kill microbes
smooths outer surface of cornea providing smooth surface for refraction
what photoreceptor is responsible for colour vision?
cones
how many different types of photoreceptor cones are there?
3
how is colour vision assessed?
ishihara plates
