Applied Anatomy and Physiology of the Orbit and Eye

Question 1

histology of the cornea

Answer 1

Epithelium – stratified squamous non-keratinised.

Bowman’s membrane (basement membrane of corneal epithelium)

Stroma – regularly arranged collagen, no blood vessels

Descemet’s layer

Endothelium – single layer (normal - 2500 cells/mm2)

Question 2

how is transparency maintained in the cornea?

Answer 2

Histologically – regular arrangement of collagen in stroma
No blood vessels
Endothelium cell layer has a pump that actively keeps the aqueous humor out.

Question 3

what is avascularity?

Answer 3

the condition of having few blood vessels or of being without blood vessels.

Question 4

what is the avascularity of the cornea?

Answer 4

benefit to surgeons when performing a graft surgery as it means there is a lesser chance of foreign antigens from a corneal graft being recognised by the recipient, so lesser chance of a graft rejection.

Question 5

what is the choroid made up of?

Answer 5

fenestrated blood vessels of varying diameter

Question 6

what are fovea centralis packed with?

Answer 6

cones, so maximum visual acuity

Question 7

functions of tear film

Answer 7

Keeps cornea moist , 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.

Question 8

how many layers does the tear film have?

Answer 8

3

Question 9

what are the contents of layer 1 of the tear film

Answer 9

mucinous layer (~30%) overlying corneal epithelium

Question 10

what are the contents of layer 2 of the tear film

Answer 10

aqueous layer (~69%) lies over the mucinous layer

Question 11

what are the contents of layer 3 of the tear film?

Answer 11

oily layer (<1%) is the most superficial

Question 12

what innervates the secretion of tears into conjunctival sac?

Answer 12

VII n