Histology of the eye

Question 1

four histological layers of the eyelid?

Answer 1

outermost layer - contiguous with skin
orbicularis oculi muscle layer
tarsal plate with stromal layer
innermost palpebral conjunctival layer

Question 2

describe the eyelid: outermost layer?

Answer 2

haired keratinised stratified squamous epithelium and tactile hairs

Question 3

what glands does the eyelid: outermost layer contain?

Answer 3

sebaceous glands (glands of Zeiss)
sweat glands (glands of Moll)

Question 4

what is the tarsal plate?

Answer 4

plate of dense connective tissue between dermis of skin and lamina propria of conjunctiva

Question 5

what glands does the tarsal plate contain?

Answer 5

contains modified sebaceous glands - tarsal glands (Meibomian glands)

Question 6

eyelid: innermost layer is lined with?

Answer 6

lined with palpebral conjunctiva - continuous with bulbar conjunctiva - continuous with corneal surface at limbus

Question 7

conjunctival epithelium of the eyelid: innermost layer?

Answer 7

it may be stratified columnar or stratified squamous and can have goblet cells

Question 8

what is the nictitating membrane of the eyelid?

Answer 8

semi-circular fold of conjunctiva enclosing a plate of cartilage

Question 9

what cartilage and gland does the nictitating membrane contain?

Answer 9

hyalin cartilage
harderian glands

Question 10

harderian glands developed in which species?

Answer 10

cows

Question 11

describe the lacrimal glands of the lacrimal apparatus in horses, ruminants, dog and pig:

Answer 11

they are seromucous glands

Question 12

describe the lacrimal glands of the lacrimal apparatus in cats:

Answer 12

serous

Question 13

describe the lacrimal glands in the lacrimal apparatus?

Answer 13

they are tubuloacinar

Question 14

where are the lymphoid follicles found?

Answer 14

seen in lamina propria of nictitating membrane

Question 15

what layers make up the globe?

Answer 15

corneo-scleral layer
uveo-vascular layer
retinal tunic

Question 16

the cornea is avascular: what does this mean that it looks like?

Answer 16

it is transparent when healthy
if vessels appear then it is in response to inflammation (neurovascularisation)
oedema (swelling with fluid) - makes cornea cloudy

Question 17

what is the cornea formed by?

Answer 17

formed of collagenous stroma (substantia propria) and mucoid ground substance collagen fibres - flattened and run parallel to surface

Question 18

outer surface of cornea?

Answer 18

it is non-keratinised stratified squamous epithelium with a basement membrane (Bowman’s membrane)

Question 19

inner surface of cornea is what?

Answer 19

it is Descemet’s membrane

Question 20

what is Descemet’s membrane?

Answer 20

it has a simple squamous epithelium on its inner surface - corneal endothelium or posterior epithelium

Question 21

erosion to the cornea?

Answer 21

loss of epithelium

Question 22

ulcer of the cornea?

Answer 22

loss of epithelium with a break in the basement membrane

Question 23

fluorescein Dye?

Answer 23

used in practice - fluoresces with UV light
Dye is hydrophilic
binds to collagen fibres
Corneal epithelium is hydrophobic
Descemet’s membrane is hydrophobic

Question 24

how does fluorescein dye work?

Answer 24

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

Question 25

sclera?

Answer 25

dense collagenous stroma with a few elastic fibres

Question 26

what is the sclera attached to?

Answer 26

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

Question 27

posterior uvea?

Answer 27

choroid

Question 28

anterior uvea?

Answer 28

ciliary body and iris

Question 29

middle vascular tunic includes?

Answer 29

includes choroid, ciliary body and iris

Question 30

ciliary body?

Answer 30

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

Question 31

choriocapillary layer contains?

Answer 31

contains a capillary network that supplies the retina

Question 32

tapetum lucidum?

Answer 32

this is found between choricocapillary and vascular layers of the choroid in dorsal portion of the eye

Question 33

herbivores: tapetum lucidum?

Answer 33

more collagen fibres so called tapetum fibrosum

Question 34

tapetum lucidum in carnviores?

Answer 34

more reflective cells so tapetum cellulosum

Question 35

iris?

Answer 35

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)

Question 36

corpora nigra?

Answer 36

sometimes called granula iridica black masses suspended from the rum of the pupil found in ungulates

Question 37

cavities of the eye in the anterior segment?

Answer 37

anterior chamber - cavity behinf the cornea in front of the iris and lens

Question 38

posterior chamber of anterior segment?

Answer 38

cavity behind the iris in front of the ciliary body

Question 39

what does anterior segment contain?

Answer 39

aqueous humour

Question 40

what does posterior segment of eye contain?

Answer 40

contains vitreous humour (body)

Question 41

posterior segment cavity?

Answer 41

cavity behind lens

Question 42

lens structure?

Answer 42

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

Question 43

what are rods and cones of the retina?

Answer 43

these are modified dendrites that act as photoreceptors

Question 44

what is the outer limiting membrane of the retina formed by?

Answer 44

formed by neuroglial processes

Question 45

what is the outer nuclear layer of the retina?

Answer 45

it is the nuclei in cell bodies of rods and cones

Question 46

what is the outer plexiform layer of the retina?

Answer 46

connecting rod and cone neurons with dendrites of the bipolar neurons

Question 47

what is the inner nuclear layer of the bipolar neurons of the retina?

Answer 47

relaying impulses between receptors and ganglion cells

Question 48

what is the inner plexiform layer of the retina?

Answer 48

it links axons of bipolar neurons and dendrites and optic nerve cells

Question 49

what cells does the ganglion cell layer of the retina contain?

Answer 49

optic nerve cells

Question 50

what is found within the nerve fibre layer of the retina?

Answer 50

the axonal processes of ganglion cells converge at the optic nerve

Question 51

what is the inner limiting membrane of the retina?

Answer 51

it is the neurological cells with processes in layer 3