vision in animals

Question 1

what is required for a large visual field and stereopsis (depth perception)

Answer 1

two eyes

Question 2

what is the job of the visual cortex

depth

Answer 2

creating 3D image form projections on 2D retinas

Question 3

angles of projection lines, and their intersection serve as:

Answer 3

range finders in stereoscopic depth detection

Question 4

green diamond

Answer 4

on plane of fixation of both eyes, so seen at same angle by both eyes, projected onto both retinas

Question 5

both purple circle and red square

Answer 5

outside plane of fixation, so seen at different angles by both eyes, projected onto disparate (but corresponding) retinal regions

Question 6

purple circle

Answer 6

closer than object of fixation, so projection lines from both eyes intersect before plane of fixation

Question 7

red square

Answer 7

further away, so projection lines from both eyes intersect after plane of fixation

Question 8

visual cues

Answer 8

• picture is 2D
• relative size, perspective, partial obstruction, and texture gradient provide depth perception of the scene

Question 9

what is visual acuity affected by

Answer 9

• refractive error of eye (where image is focused)
• accommodation (bringing image into focus on retina by changing lens curvature or position)
• pupil size, globe size
• rod and cone concentration

Question 10

what is snellen chart

Answer 10

size of letters that patient can read at distance of 20 ft, or 6m

Question 11

veterinary patients nonverbal, so calculate acuity based on:

Answer 11

• behavioral discrimination tests
• electro-physiologic recordings to determine smallest pattern that elicits ERG or cortical response
• eye responses to determine smallest stimulus that elicits tracking eye movements
• theoretical calculations based on cone or RGC density

Question 12

larger globe size

Answer 12

• longer posterior focal distance (between lens, retina)
• results in larger retinal image, higher visual resolution
• image can be sampled, processed by more photoreceptors, ganglion cells than in smaller globe

Question 13

AC depth and lens thickness

Answer 13

• light exiting lens has relatively long path before it reaches retina in human, short path before it reaches retina in cat
• feline lense needs to have significantly greater power than human lens; this is made possible by greater curvature
• dog has intermediate values in AC depth, lens location, lense curvature