Lecture 3 - Ocular physiology

Question 1

Define orbit.

Answer 1

It is the bony socket that holds the eye. It’s purpose is to protect the delicate eye and it provides a mounting point of the striatal muscle that control ocular movement.

Question 2

What is the sclera?

Answer 2

It is the tough outer protective coat.

Question 3

What is the lens?

Answer 3

It is a transparent biconvex structure suspended by lens zonules.

Question 4

What does the cilliary body do?

Answer 4

It provides attachment for the lens zonules and changes focusing power of the lens

Question 5

What is the purpose of the iris?

Answer 5

The iris controls the amount of light entering the eye.

Question 6

What is the choroid?

Answer 6

It maintains the blood supply to the eye

Question 7

What is the retina?

Answer 7

It is the inner layer that has all the visual photoreceptors.

Question 8

What is the purpose of the optic nerve?

Answer 8

It transmits images from the retina to the brain.

Question 9

What is the name of the gland that produces tear?

Answer 9

Lacrymal gland

Question 10

Name the 2 types of tears and their differences.

Answer 10

Basic tears (to maintain tear film over the cornea)
Reflex tears (in response to mechanical or chemical irritation, light or cold)

Question 11

What is the precorneal tear film composed of?

Answer 11

It is composed of three layers namely:
superficial lipid layer
central aqueous layer
inner mucus layer

Question 12

What is the lipid layer made of and what is the purpose of the lipid layer?

Answer 12

It is mainly made of free sterols and fatty acids
It spreads over the aqueous layer during eye opening and it reduces the evaporation rate to maintain the osmolality of tear.

Question 13

What is the aqueous layer made of?

Answer 13

Inorganic salts
Urea
Glucose
Retinol
Ascorbic acid
Lipocalins
Glycoproteins
Immunoglobins
Lysozyme
Lactoferrin

Question 14

List the functions of the tear film

Answer 14

• Prevention of corneal drying
• Transport of oxygen and nutrients to the cornea
• Maintenance of cornea smooth and clean
• Protection against infection

Question 15

What is the normal tear volume at normal conditions?

Answer 15

7-9 microlitres

Question 16

What is the purpose of blinking?

Answer 16

It is a defense mechanism to prevent high speed objects approaching the eye. It is also essential to reform the tear film.

Question 17

What are the functions of the cornea?

Answer 17

Passage of light
Refraction of light
Protection

Question 18

What is the composition of the aqueous humour (the fluid found inside the chamber of the eye)?

Answer 18

98% water
Amino acids
Electrolytes
Ascorbic acid
Glutathione
Immunoglobulins

Question 19

What are the functions of the aqueous humour?

Answer 19

• Maintain intraocular pressure and inflates the globe of the eye.
• It provides nutrition to the avascular ocular tissues.
• Fights infections (immunoglobulins)
• Transport ascorbate to the anterior to act as an anti-oxidant agent.
• Light refraction

Question 20

What is the purpose of the lens?

Answer 20

Along with the cornea, it helps to refract light onto the retina. It is elastic which allow it to change shape depending on how it should focus.

Question 21

What is the purpose of the vitreous humour?

Answer 21

It is the clear gel that fills the space between the lens and the retina.
It serves the purpose of maintaining the normal anatomic expansion of the globe.
Allow diffusion of substances to the retina
Small water soluble substances in the retina can diffuse into the vitreous across the blood retina barrier.
Acts as a reservoir for oxygen, glucose and ascorbic acid to maintain metabolism.
Acts as a reservoir for metabolic waste products as well.

Question 22

List the composition of the vitreous humour

Answer 22

Water
Network of collagen fibrils
Large molecules of hyaluronic acid
Peripheral cells
Inorganic salts
Glucose
Ascorbic acid

Question 23

What are photoreceptors?

Answer 23

They are cone or rod shaped, which are located on the retinal surface. The rods activate upon low light and the cone upon high light.
The cone allow colour perception and spatial resolution

Question 24

What is the purpose of the optic nerve?

Answer 24

The photoreceptors activate AP in the optic nerve. It is a bundle of approx. 1.25 e8 nerves. They transmit images from the retina to the brain specifically the visual cortex found in the occipital lobes.