Lecture 6- Vision I: The Retina Flashcards
Describe the anatomy of the eye:
-cornea right at the front= clear surface, the light passes through -lens bends the light and this is focused on the retina -retina= 5/6 of the back of the eyeball -eyeball like an onion= outer layer= there for keeping strength, -middle layer= lot of blood vessels for nutrition -and the inside layer= retina= constitutes all of the nerves that allow us to see, -optic nerve= contains the axons of the ganglion cells as they go off to the brain
What does the retina look like normally?
-when you look into it with an opthalamoscope(expensive torch) -whitish thing= where the axons go into the brain pinky thing= fovea (also called macula)
What does the fovea (macula) do?
-this is the most important of the eye, allows you to see centrally, allows you to read, see faces, and see dead centre, all the rest is for peripheral
What are the optical factors affecting visual acuity?
- Pupil size 2.Clarity of optical media- cataracts, corneal opacities 3.Refractive errors-myopia, hypermetropia, astigmatism and presbyopia
How does pupil size affect visual acuity?
-the smaller the pupil size, the clearer the vision -if a large pupil can’t see as well at night
How does the clarity of optical media affect visual acuity?
-how the light passes through the eye: if any of the structures that the light must pass through are effected (scarred) then this will effect the baility to see
How do refractive errors affect visual acuity?
-if the size of the eyeball is not the right length= then the focusing doesn’t work and vision= blurry -if the eyeball is mismatch (size-wise) = refractive error
What is myopia?
-shortsighted= the eyeball is too long and the light focuses it is too early, in front of the back of the eye= shortsigted
What is hypermetropia?
-Hypermetropia= the eyeball is too small=the light is focused behind the back of the eye, not focused as much on the retina
What is astigmatism?
-Astigmatism:surface of the eye is squashed a bit (like rugby ball) as the light goes through the cornea it creates two focuses, one might be clear in one domain and the other domain it’s completely blurry
What is presbyopia?
-feel like arms not long enough= the process that allows us to read, to focus on sth closer becomes impaired and eventually may need glasses
Why are the photoreceptors of the retina at the bottom?
cross section through the back of the eyeball -series of neuron layers -follow the light- it has to go through all the layers of the retina before it hits the photoreceptors -they are the light detectors, they respond to light and create the neural signal that allows us to see -why does it seem back to front? -because of the cells that sit underneath the retina: retinal pigmental epithelial cells, very important to keep the retinal cells alive, if it were switched around then the pigmented cells wouldn’t let light through= too dense -the retinal pigmented cells= provide nutrition to retinal cells
What are the characteristics of rods?
-night vision (scotopic) -very sensitive -only one type -black and white, no colour vision -100million =95% of all photoreceptors -absent from the fovea
What are the characteristics of cones?
-day vision (photopic) -less sensitive -three types (red, blue and green) -allow colour vision -5 million (only about 5% of the photoreceptors) -densest in the fovea
What is the ratio of rods to cones?
20:1