Lecture 3 - Ocular physiology Flashcards
Define orbit.
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.
What is the sclera?
It is the tough outer protective coat.
What is the lens?
It is a transparent biconvex structure suspended by lens zonules.
What does the cilliary body do?
It provides attachment for the lens zonules and changes focusing power of the lens
What is the purpose of the iris?
The iris controls the amount of light entering the eye.
What is the choroid?
It maintains the blood supply to the eye
What is the retina?
It is the inner layer that has all the visual photoreceptors.
What is the purpose of the optic nerve?
It transmits images from the retina to the brain.
What is the name of the gland that produces tear?
Lacrymal gland
Name the 2 types of tears and their differences.
Basic tears (to maintain tear film over the cornea) Reflex tears (in response to mechanical or chemical irritation, light or cold)
What is the precorneal tear film composed of?
It is composed of three layers namely:
superficial lipid layer
central aqueous layer
inner mucus layer
What is the lipid layer made of and what is the purpose of the lipid layer?
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.
What is the aqueous layer made of?
Inorganic salts Urea Glucose Retinol Ascorbic acid Lipocalins Glycoproteins Immunoglobins Lysozyme Lactoferrin
List the functions of the tear film
- Prevention of corneal drying
- Transport of oxygen and nutrients to the cornea
- Maintenance of cornea smooth and clean
- Protection against infection
What is the normal tear volume at normal conditions?
7-9 microlitres
What is the purpose of blinking?
It is a defense mechanism to prevent high speed objects approaching the eye. It is also essential to reform the tear film.
What are the functions of the cornea?
Passage of light
Refraction of light
Protection
What is the composition of the aqueous humour (the fluid found inside the chamber of the eye)?
98% water Amino acids Electrolytes Ascorbic acid Glutathione Immunoglobulins
What are the functions of the aqueous humour?
- 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
What is the purpose of the lens?
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.
What is the purpose of the vitreous humour?
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.
List the composition of the vitreous humour
Water Network of collagen fibrils Large molecules of hyaluronic acid Peripheral cells Inorganic salts Glucose Ascorbic acid
What are photoreceptors?
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
What is the purpose of the optic nerve?
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.
