Physiology of Vision- Graf Flashcards
The eye requires coordination of many things.
If you add all the components of outline: color, color contrast, #d then you have a total picture of everything. ?????
Eye disease prevalence
Eye disease:
Myopia, hyperopia, cataracts, retinal
Almost 25% of the population suffer from eye diseases.
Examples of Eye disease
myopia: blurred vision
age related macular degeneration: area of sharpest vision is degraded
cataract: cloudy lens, blurred vision; is preventable
glaucoma: high intracranial pressure and retina gets destroyed from the periphery
diabetic retinopathy: occurs when high blood sugar levels cause damage to blood vessels in the retina; degeneration of BVs
The eye can only take in a narrow range of frequency. Why?
-narrow range of frequency we can see because we evolved from water dwelling animals
16 Hz – 20 kHz
400-700 nm (visible light)
Eye structure
Sclera is tough you need a razor blade to go through it.
Vitreous humour (flow out and eye will collapse) and aqueous humor produced by the ciliary body. It is evacuated by the Canal of Schlemm.
Pupil is defined by its surrounding (iris).
Iris means rainbow and is responsible for the color of our eyes.
Cornea are the strongest refractive surface. Lens has some refractory surface.
Choroid surrounds the eye and is abundant with BVs responsible for providing nutrients to the eye.
Retina have the photoreceptors.
Eye embryology
- eye comes from the optic vesicle which invaginates back on itself
- optic nerve is part of the brain (not a real nerve)
- eye is formed from the neural ectoderm (makes the retina) and the surface ectoderm (makes the cornea and lens)
all eyes have photoreceptors and lens to focus the images (no matter what species we’re talking about)
Ciliary muscle vs Iris
Ciliary muscle is a circular muscle for far/near objects. It is antagonist to the elasticity of the lens. Under normal conditions the ciliary muscle is relaxed and the lens are pulled flat. When you want to accomodate or look at something near, the ciliary muscle contract and pulls against the lens elasticity allowing focus. When you get older your eyes lose elasticity, so you need glasses to see things.
Iris is for constriction/dilation of pupil. Dilator pupillae is by sympathetic system and sphincter pupillae is by the parasympathetic system.
Atropine eye drops is a parasympathetic antagonist so parasympathetic muscle cannot work (sphincter pupillae cannot constrict and ciliary muscle cannot contract to make lens thicker for focus).
What are the external eye muscle?
- lateral rectus
- medial rectus
- superior rectus
- inferior rectus
- superior oblique
- inferior oblique
What is emmetropia, hyperopia, and myopia?
Emmetropia: normal sighted: image hits directly on the retina
Hyperopia: the image gets formed behind the retina getting a blurred image; to shorten the optical power; far-sighted; correct with convex lenses
Myopia: to long the optical power; the image gets formed in front of the retina and the image is blurred; near sighted; correct with concave lenses
What is astigmatism and presbyopia?
Astigmatism: non-spherical aberration of the cornea
Presbyopia: old sighted; need reading glasses; a gradual, age-related loss of the eyes’ ability to focus actively on NEARBY objects
Snellen Chart
- measures visual functions
- 20/20 vision is at the 8th line (a normal sighted person)
- the visual system works on two things: a linear system that works on spatial frequency (how much you can discern the minimum resolution you get which depends on your optical powers and density of photoreceptors) and contrast
high contrast means low spatial frequency AND
low contrast means high spatial frequency means you can’t see the letters
Snellen chart has sloan letters. They work on the spatial frequency detection of the visual system. One letter element 1 minute of arc. Period- 2 minutes of arc.
60 minutes an arch?????
Retina
100,000,000 photoreceptors in each eye (100 million)
- we have rods and cones
- 15 types of bipolar, horizontal, 30 types of amacrine, and 45 types of ganglion cells)
-retinal ganglion gives rise to the optic nerve (optic nerve are the axons of retinal ganglion)
lateral information flow: horizontal and amacrine cells
information throughput: bipolar and ganglion ??????
Rods and cone
rods and cones distributed preferentially
on the fovea you only have cones
parafovea you have rod peak. At the fovea you have cone peak???????
macula which contains the fovea; has 50% of input to brain
1:0.5 ??????
fovea: one cone for two retinal ganglion cells; receptor fields are very big and images are sharp
periphery: one cone for 50-100 retinal ganglion cells
We have 3 cone types, what are they?
We are tri-chromatic. Three cone photopigments.
red
green
blue
with different peaks in the light spectrum
photopic vision is color vision (cones)
scotopic vision is night vision (rods) ?????
One rod photopigment
- Rhodopsin
- colorblindness
can you read the number 8 image