Histology of the eye

Question 1

4 histological layers of the eyelid

Answer 1

• outermost layer
• orbicularis oculi; muscle layer
• tarsal plate with stromal layer
• innermost palpebral conjunctival layer

Question 2

Outer layer of the eyelid

Answer 2

Haired keratinised stratified squamous epithelium and tactile hairs
- sebaceous glands; glands of Zeiss
- sweat glands; glands of Möll

Question 3

Innermost layer of the eyelid

Answer 3

Lined with palpebral conjunctiva, continuous with bulbar conjunctiva and corneal surface at limbus
- conjunctival epithelium can be stratified columnar or stratified squamous

Question 4

Tarsal plate

Answer 4

Plate of dense connective tissue between dermis of skin and lamina propria of the conjuctiva
- contains modified sebaceous glands; Meibomian Glands

Question 5

Tarsal plate

Answer 5

Plate of dense connective tissue between dermis of skin and lamina propria of the conjunctiva
- contains modified sebaceous glands; Meibomian Glands

Question 6

Nictitating membrane

Answer 6

Semi-circular fold of conjunctiva enclosing a plate
of cartilage

Question 7

Lacrimal Apparatus

Answer 7

• Lacrimal Glands; Tubuloacinar, serous (cats), seromucous (horse, ruminant, dog and pig)
• Lymphoid follicles; Seen in lamina propria of nictitating membrane

Question 8

The globe

Answer 8

• Corneo-scleral layer
• Uveo-vascular layer
• Retinal tunic

Question 9

Cornea

Answer 9

• avascular; transparent when healthy
  -if vessels; respond to inflammation (neovascularisation)
• Oedema; swelling with fluid makes cornea cloudy
• Formed collagenous stroma and mucoid ground substance
• Outer surface is non-keratinised stratified squamous epithelium with basement membrane (Bowman’s membrane)
• Inner surface of the cornea is Descemet’s membrane
• Descemet’s membrane has simple squamous epithelium on inner surface- corneal endothelium

Question 10

Injuries to the cornea

Answer 10

• erosion; loss of epithelium
• ulcer; loss of epithelium with a break in the basement membrane
• Use fluorescein dye; binds to collagen fibres, if applied to healthy cornea, washes away

Question 11

Sclera

Answer 11

• dense collagenous stroma with few elastic fibres
• attached to the middle tunic (choroid) by the lamina fusca (layer of pigmented connective tissue)
• optic nerve passes through the sclera at the lamina cribrosa

Question 12

Areas of Uvea

Answer 12

• posterior uvea; choroid
• ## anterior uvea; ciliary body & iris

Question 13

Ciliary body

Answer 13

• anterior continuation of the choroid
• inner surface is a continuation of non-light-sensitive retina
• stroma contains ciliary muscle (smooth)
• basal epithelial layer; pigmented columnar cells
• surface epithelial layer; non-pigmented columnar cells

Question 14

Choriocapillary layer

Answer 14

contains the capillary network that supplies the retina with blood

Question 15

Tapetum lucidum

Answer 15

• between choriocapillary and vascular layers of the choroid in the dorsal part of the eye

Question 16

Iris

Answer 16

• most anterior portion of the uvea
• attached to the ciliary body
• connective tissue stroma supports many blood
  vessels and contains pigment cells
• only posterior surface has pigment cells
• anterior surface has melanocytes and fibrocytes
• corpora nigra; black masses suspended from rim of pupil in ungulates

Question 17

Layers of the photosensitive retina

Answer 17

1) Retinal pigmented epithelium
2) Rods and cones; photoreceptors
3) Outer limiting membrane
4) Outer nuclear layer
5) Outer plexiform layer
6) Inner nuclear layer of bipolar neurones
7) inner plexiform layer
8) ganglion cell layer
9) nerve fibre layer
10) inner limiting membrane

Question 18

Cavities of the eye

Answer 18

• anterior segment; aqueous humour. Anterior chamber (behind cornea in front of iris and lens) and posterior chamber ( behind iris in front of ciliary body)
• Posterior segment; vitreous humour; cavity behind the lens

Question 19

THE LENS

Answer 19

• lens capsule; basement membrane of lens epithelium, elastic properties
• lens epithelial cells; proliferation zone, nuclear bow and elongation and turnover of LECs
• lens fibres
  -lens sutures