VETS2011 Lecture 12: VETS2011 Neurophysiology Lecture 12
Vision
Light refraction
Bending of light waves when they hit a surface due to differences in times
they hit the surface, decreased velocity of transmission and changes
in wavelength. A convex lens refracts light as the beams
go from the air through the eye.
The eye
• 4 refractive interfaces
1. Air and anterior cornea
2. Posterior cornea and aqueous humor
3. Aqueous humor and surface lens
4. Posterior lens and vitreous humor
•Les can increase/decrease curvature for accommodation
•Les focuses the image on retina as inverted
Errors of refraction
1. Emmetropia: Normal vision
2. Hypertropia: Far light not bent enough, short eyeball or weak lens. Focal
point after the retina
3. Myopia: Cat fous ea ojets, log eyeall o too uh efatio.
Focal point before retina.
4. Astigmatism: Planes focus differently due to difference in curvature of
lens planes
5. Cataracts: Cloudy lens obscures light transmission.
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Common cause of blindness in dogs
- Cataract
- Solution: Remove the lens. Still got vision because got other surfaces to
refract light, just not that good.
- Or more expensive, replace lens.
Depth perception is achieved by:
Size of image of known objects on retina
- Knowing the size and comparing it with image size. If you know tree is
big, if you see it small you auto assume it is small.
Moving parallax
- Used by birds
- Moving head from side to side. Close by images move quicker (e.g.
Moving train)
Stereopsis
- For creatures with eyes on front of head.
- Image from 2 eyes slightly different on each retina.
Different animals have different visual fields
- Because different eye positions
- Different visual fields evolved to match the purpose.
- Stereoptic vision: Good for estimating distance accurately when hunting.
- Eyes either side: Less good for depth perception, but good for big visual
field to see all around to keep eye out for predators. (Horse only blind
spot is at the back, so flight or fight reaction when approached from
behind)
Sensory Detection
- Changing light stimulus to neural, to carry action potentials from back of
retina to optic nerve to brain to intepret.
Light reception: Changing light to neural
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Bending of light waves when they hit a surface due to differences in times they hit the surface, decreased velocity of transmission and changes in wavelength. A convex lens refracts light as the beams go from the air through the eye. The eye: 4 refractive interfaces, air and anterior cornea, posterior cornea and aqueous humor, aqueous humor and surface lens, posterior lens and vitreous humor, le(cid:374)s can increase/decrease curvature for accommodation, le(cid:374)s focuses the image on retina as inverted. Errors of refraction: emmetropia: normal vision, hypertropia: far light not bent enough, short eyeball or weak lens. Focal point after the retina: myopia: ca(cid:374)(cid:859)t fo(cid:272)us (cid:374)ea(cid:396) o(cid:271)je(cid:272)ts, lo(cid:374)g eye(cid:271)all o(cid:396) too (cid:373)u(cid:272)h (cid:396)ef(cid:396)a(cid:272)tio(cid:374). Focal point before retina: astigmatism: planes focus differently due to difference in curvature of lens planes, cataracts: cloudy lens obscures light transmission. Still got vision because got other surfaces to refract light, just not that good. Size of image of known objects on retina.
