Basic Science Oph Chapter 2 Physiology

Question 1

Function of tear film

Answer 1

1)maintaining the smooth optical properties of the corneal surface
2)providing oxygen to the avascular cornea,
3)lubricating the interface between the lids and the cornea,
4)Removal of foreign bodies, debris, and cells,
5)providing antibacterial properties to the cornea.

Question 2

Three layers to the tear film:

Answer 2

● deep mucous layer (30–40%)
● middle aqueous layer (60%)
● surface oily layer

Question 3

Mucus layer made from

Answer 3

The mucus layer is made from epithelial cell glycocalyx and
a layer of tear mucins (glycoproteins) produced by the conjunctival goblet cells.

Question 4

Goblet cells location

Answer 4

The goblet cells are particularly aggregated in the tarsal conjunctival crypts (Henle’s crypts) and on the bulbar conjunctiva nasal to the limbus (Manz’s glands).

Question 5

The aqueous component of the tear film (thickness and secretion by what)

Answer 5

The aqueous component of the tear film (7–10 μ m thick) is
produced by the lacrimal gland and its accessory glands

Question 6

The lipid layer (thickness)

Answer 6

The lipid layer (0.2–1 μ m thick) is formed from polar and
neutral lipids by meibomian gland secretion (holocrine secretion) and is the thinnest layer (0.1 μ m).

Question 7

Aqeuous layer consist of

Answer 7

It is 98% water with a solution of electrolytes (particularly K + and
Cl –) and protein, including immunoglobin A (IgA), lactoferrin,
G protein, tear-specific prealbumin, and lysozyme.

Question 8

Basal tear secretion rate

Answer 8

Basal tear secretion is 1.2 μ l/min

Question 9

Ciliary body has a role in:

Answer 9

● accommodation
● aqueous humour production
● production of lens zonules
● production of vitreal glycosaminoglycans and collagen
● non-conventional aqueous outflow.

Question 10

% of the aqueous fluid drains through the uveoscleral route.

Answer 10

About 10% of the aqueous fluid also drains through the
uveoscleral route.

Question 11

Aqueous humour is produced at a rate of approximately

Answer 11

Aqueous humour is produced at a rate of approximately
2–3 μ l/min.

Question 12

Three physiologic processes contribute to the formation of aqueous humour:

Answer 12

● diffusion
● ultrafiltration (and the related dialysis)
● active secretion ( Normally, 80–90% of total aqueous humour formation is by active secretion)

Question 13

Active secretion mediated by two enzymes:

Answer 13

● sodium–potassium-activated adenosine triphosphate (Na + –
K + -ATPase)
● carbonic anhydrase.

Question 14

Composition of aqueous humour compared
to plasma

Answer 14

The main differences result from the low protein and high
ascorbate concentrations (200 times less and 20 times
greater, respectively). The ascorbate is thought to reduce
oxidative damage from UV radiation. Lactate levels are also
elevated due to glycolysis in the cornea, lens, and other ocular structures.