CHAPTER 14- Ocular anatomy and physiology Part 2 (1) Flashcards
What is the crystalline lens?
The crystalline lens provides refractive power and allows the eye to focus on objects at different distances.
What 3 layers does the crystalline lens consist of?
1- An elastic capsule covering the entire surface
2- A simple epithelium underneath this
3- The bulk of the lens is made of elongated cells (lens fibres)
What are lens fibres?
Lens fibres are long hexagonal cells that run from the front to the back surface of the lens.
Adjacent lens fibres are joined by what and what does it allow?
Adjacent lens fibres are joined by gap junctions to allow the flow of nutrients.
What do the elastic properties of the capsule ensure?
Ensures that the lens’s natural state is thick and round.
The lens is suspended within a ring of fibrous strands called…
Zonules
What are zonules composed of?
Composed of cysteine- rich fibrillin, giving them elasticity.
Where do the zonules run along?
The zonule fibres run along the ciliary body and attached to the pars plana.
When the ciliary muscle contracts, what happens to the diameter of the ciliary body and what does this allow?
The diameter of the ciliary body decreases.
This allows the zonule fibres to go lax (relax).
This results in the lens becoming thicker and rounder.
What happens to the lens when the ciliary muscle is contracted?
The lens becomes wider and more curved, increasing its refractive power.
This allows the eye to focus on near objects (accommodation)
Is the vitreous chamber the largest of the three chambers?
Yes
Where is the vitreous chamber located?
Located behind the lens and in front of the retina.
What is the vitreous chamber filled with?
This is filled with vitreous humour
What is the vitreous humour?
A clear gel, which is more viscous than aqueous.
Viscous- much more substance to it.
What does the vitreous humour consist of?
It is 99% water, with just a few cells as well as some salts, sugars, plus a network of collagen fibrils extend throughout to make it gel- like.
What is the main function of the vitreous humour?
Provides support for the eyeball.
With age, what happens to the vitreous humour?
With age, collagen fibres degrade and the vitreous starts to liquify.
The fibres holding the surrounding membrane to the retina can break, potentially leading to small floaters or even complete vitreous detachment.
What is the retina?
Receives information and sends it to the brain through the optic nerve.
What does the retina line?
The retina lines the back of the eye
What is the retina composed of?
It is composed of neurons, gilia, epithelial cells, and blood vessels, etc.
How are the layers in the retina arranged?
Back to front
What are the photoreceptors in the retina and what do they do?
The photoreceptors are the sensory receptors that convert the optical image into nervous potentials.
Cones and rods are designed for what levels?
Cones are designed for high light levels
Rods are designed for low light levels
How does the retinal pigment epithelium (RPE) support the photoreceptors?
It transports nutrients to the photoreceptor cells and removes waste products from photoreceptor cells.
The retina is made up of 5 main types of neurons:
1- Photoreceptors 2- Horizontal cells 3- Bipolar cells 4- Amacrine cells 5- Ganglion cells
