*L06 - Vision Flashcards
What are the three layers of the eye made up of?
The outermost layer is the sclera with the cornea anteriorly
The middle layer is the choroid with the iris anteriorly
The innermost layer is the retina with the lens anteriorly
What are the two types of humor in the eye and where are they?
There is vitrous humour that is behind the lens and jelly like, this makes up the majority of the volume of the eye and gives it its shape.
There is aqueous humor that is infront of the lens and is more watery.
What is the purpose of the aqueous humor?
To nourish the cornea as it does not have any blood suppy.
Where is aqueous humor produced and reabsorbed?
It is produced in the posterior chamber behind the iris. It then moves through the pupil into the anterior chamber where it is reabsorbed in the scleral venous sinus.
What can cause glaucoma and how can it be treated?
It is caused by lack of removal of aqueous humor resulting in the build up of pressure. This can be due to angle closure from the cornea adhereing to the iris blocking drainage. Can also have open angle where the veins thicken which reduces reabsorption. It can be treated with surgery or a beta blocker to reduce secretion of aqueous humor.
In the retina which cells create the inital action potential?
The ganglion cells not the photoreceptors or bipolar cells
What is the structure of organisation of cells in the retina?
Light is detected by photoreceptor cells which pass this information on to bipolar cells that pass it to ganglion cells. There are horizontal and amacrine cells which modulate the transmission. Photoreceptors are at the bottom and ganglion cells at the top closest to the light.
What is the structure of rod cells and what chemicals do they contain?
Rods have a large number of intracellular membrane discs which contain only the chemical rhodopsin. This large surface area created by the many discs results in very sensitive vision so used at night
What is the structure of cone cells and what chemicals do they contain?
Cones have folds in their surface membrane to form the light sensitive area. This has a smaller surface area than the rods so is less sensitive. It contains 3 opsins for red, green and blue.
What causes the blind spot?
The optic disc where the optic nerve enters the eye.
Why is the periperal vision more sensitive to light?
There are more rods than cones so more pigment
Each ganglion connects to more than one rod so all signals are combined from low light intesity so can create an action potential.
Due to this though it has low visual acuity.
Why does the fovea have better acuity than the periphery?
Fovea has low sensitivity to light but high visual acuity
Has 1:1 cone to ganglion cell, therefore has to be receiving high enough intensity of light to cause an
AP to be transmitted.
Also displacement of other cells so light can directly hit photoreceptors
What happens to both types of photoreceptors in terms of volttage when light hits them?
They hyperpolarise
What is rhodopsin made up of?
It is made up of retinal (chromophore) and opsin (g protein coupled receptor
What happens in rods in the dark and then in the light?
In the dark rhodopsin is inactive and this means that the cation channels are open that allows mainly Na+ through. This is called a dark current and causes depolarisation. Resting potential of -30mV.
When light hits it retinal activates GPCR opsin and this closes the channel so sodium cannot enter and the cell hyperpolarises.
