Histology of the eye Flashcards
four histological layers of the eyelid?
outermost layer - contiguous with skin
orbicularis oculi muscle layer
tarsal plate with stromal layer
innermost palpebral conjunctival layer
describe the eyelid: outermost layer?
haired keratinised stratified squamous epithelium and tactile hairs
what glands does the eyelid: outermost layer contain?
sebaceous glands (glands of Zeiss)
sweat glands (glands of Moll)
what is the tarsal plate?
plate of dense connective tissue between dermis of skin and lamina propria of conjunctiva
what glands does the tarsal plate contain?
contains modified sebaceous glands - tarsal glands (Meibomian glands)
eyelid: innermost layer is lined with?
lined with palpebral conjunctiva - continuous with bulbar conjunctiva - continuous with corneal surface at limbus
conjunctival epithelium of the eyelid: innermost layer?
it may be stratified columnar or stratified squamous and can have goblet cells
what is the nictitating membrane of the eyelid?
semi-circular fold of conjunctiva enclosing a plate of cartilage
what cartilage and gland does the nictitating membrane contain?
hyalin cartilage
harderian glands
harderian glands developed in which species?
cows
describe the lacrimal glands of the lacrimal apparatus in horses, ruminants, dog and pig:
they are seromucous glands
describe the lacrimal glands of the lacrimal apparatus in cats:
serous
describe the lacrimal glands in the lacrimal apparatus?
they are tubuloacinar
where are the lymphoid follicles found?
seen in lamina propria of nictitating membrane
what layers make up the globe?
corneo-scleral layer
uveo-vascular layer
retinal tunic
the cornea is avascular: what does this mean that it looks like?
it is transparent when healthy
if vessels appear then it is in response to inflammation (neurovascularisation)
oedema (swelling with fluid) - makes cornea cloudy
what is the cornea formed by?
formed of collagenous stroma (substantia propria) and mucoid ground substance collagen fibres - flattened and run parallel to surface
outer surface of cornea?
it is non-keratinised stratified squamous epithelium with a basement membrane (Bowman’s membrane)
inner surface of cornea is what?
it is Descemet’s membrane
what is Descemet’s membrane?
it has a simple squamous epithelium on its inner surface - corneal endothelium or posterior epithelium
erosion to the cornea?
loss of epithelium
ulcer of the cornea?
loss of epithelium with a break in the basement membrane
fluorescein Dye?
used in practice - fluoresces with UV light
Dye is hydrophilic
binds to collagen fibres
Corneal epithelium is hydrophobic
Descemet’s membrane is hydrophobic
how does fluorescein dye work?
binds to collagen fibres
if applied to healthy cornea - washes away with tear film
does not bind to intact corneal epithelium (hydrophobic)
if ulcer present - dye binds to exposed stroma (hydrophilic)
see a fluorescent spot in the shape of the ulcer
Descemet’s membrane does not bind the dye (hydrophobic)
If ulcer reaches Descemet’s membrane (Descemetocele) - no fluorescence
sclera?
dense collagenous stroma with a few elastic fibres
what is the sclera attached to?
attached to the middle tunic (choroid) by the lamina fusca which is a layer of pigmented connective tissue
optic nerve passes through sclera at the lamina cribrosa
posterior uvea?
choroid
anterior uvea?
ciliary body and iris
middle vascular tunic includes?
includes choroid, ciliary body and iris
ciliary body?
this is the anterior continuation of choroid
inner surface is continuation of a non-light sensitive retina (pars ciliaris retinae)
stroma contains ciliary muscle (smooth muscle)
basal epithelial layer - pigmented columnar cells
surface epithelial layer - non pigmented columnar cells
choriocapillary layer contains?
contains a capillary network that supplies the retina
tapetum lucidum?
this is found between choricocapillary and vascular layers of the choroid in dorsal portion of the eye
herbivores: tapetum lucidum?
more collagen fibres so called tapetum fibrosum
tapetum lucidum in carnviores?
more reflective cells so tapetum cellulosum
iris?
most anterior part of uvea
attached to the ciliary body
muscular diaphragm rostral to the lens with central opening (pupil)
connective tissue stroma supports many blood vessels and contains pigment cells
only posterior surface has pigmented epithelium (pars iridica retinae)
anterior surface - fibrocytes and melanocytes (no epithelium)
corpora nigra?
sometimes called granula iridica
black masses suspended from the rum of the pupil
found in ungulates
cavities of the eye in the anterior segment?
anterior chamber - cavity behinf the cornea in front of the iris and lens
posterior chamber of anterior segment?
cavity behind the iris in front of the ciliary body
what does anterior segment contain?
aqueous humour
what does posterior segment of eye contain?
contains vitreous humour (body)
posterior segment cavity?
cavity behind lens
lens structure?
Lens capsule: basement membrane of lens epithelium and has elastic properties
Lens epithelial cells: proliferation zone and nuclear bow and elongation and turnover of LECs
Lens fibres
Lens sutures
what are rods and cones of the retina?
these are modified dendrites that act as photoreceptors
what is the outer limiting membrane of the retina formed by?
formed by neuroglial processes
what is the outer nuclear layer of the retina?
it is the nuclei in cell bodies of rods and cones
what is the outer plexiform layer of the retina?
connecting rod and cone neurons with dendrites of the bipolar neurons
what is the inner nuclear layer of the bipolar neurons of the retina?
relaying impulses between receptors and ganglion cells
what is the inner plexiform layer of the retina?
it links axons of bipolar neurons and dendrites and optic nerve cells
what cells does the ganglion cell layer of the retina contain?
optic nerve cells
what is found within the nerve fibre layer of the retina?
the axonal processes of ganglion cells converge at the optic nerve
what is the inner limiting membrane of the retina?
it is the neurological cells with processes in layer 3
