Vision Physio & Clinical

Question 1

What benefits do convergence and divergence have? at what cost?

Answer 1

Conv: increased sensitivity, decreased acuity (i.e. rods)
Div: decreased sensitivity, increased acuity (i.e. cones, and projections from occ cx)

Question 2

What are M cells and P cells?

Answer 2

Magno- and parvo-cellular RGCs. M: large receptive field, sensitive, for peripheral/night vision. P: small receptive field, good acuity, central/macular vision

Question 3

To which cells does center-surround antagonism apply?

Answer 3

Bipolar neurons, RGCs, LGN

Question 4

What are ON and OFF cells?

Answer 4

ON: light in center excites neuron, dark inhibits
OFF: light in center inhibits, dark excites

Question 5

How do center and surround cells affect bipolar cell?

Answer 5

Center: direct to bipolar cell
Surround: via inhibitory horizontal cell (lateral inhibition)

Question 6

What is the function of ocular dominance columns? Ocular orientation columns? Blob channels?

Answer 6

ODC: depth perception
OOC: where/mvmt and what/shape
Blob: color

Question 7

What is amblyopia?

Answer 7

“Lazy eye” that affects ocular dominance columns to avoid diplopia; causes loss depth/spatial perception

Question 8

What is strabismus?

Answer 8

Misaligned eyes due to muscle problems, CN problems, etc. May cause diplopia, loss of depth/spatial perception

Question 9

What are treatment options for amblyopia?

Answer 9

Patch good eye and force use of bad eye, blur good eye with cholinergic blockers

Question 10

Describe the M-channel/movement pathway.

Answer 10

M-RGC (periphery retina) -> certain LGN layers -> certain V1 areas (OOC) -> certain visual assc areas -> post par cx

Question 11

Describe the P-channel/shape pathway.

Answer 11

P-RGC (central retina) -> certain LGN layers -> certain V1 areas (OOC) -> certain visual assc areas -> fusiform gyrus

Question 12

What deficit occurs with lesion of fusiform gyrus?

Answer 12

Inability to recognize familiar faces, even your own

Question 13

Describe the blob channel/color pathway.

Answer 13

Non-P/M-RGC (central) -> certain LGN layers -> certain V1 areas -> certain assc cx areas -> fusiform gyrus

Question 14

What is diabetic retinopathy? How does it affect type 1 and type 2 differently? What are signs of it?

Answer 14

Type 1: nearly all have some
2: Most (60%) have some
Microvessel problems lead to micro-aneurysms, -hemorrhages, vessel proliferation

Question 15

What are the clinical features and progression of retinitis pigmentosa?

Answer 15

Slowly progressive photoreceptor degen causing rod loss, tunnel vision, then cone loss and retinal degeneration

Question 16

How does light cause a neural signal?

Answer 16

Photopigments isomerize, increase cGMP PDE to decrease cGMP, close cGMP-gated Na channels -> hyperpolarize by decreasing glutamate release

Question 17

How do vitamins A and E and lutein affect retinitis pigmentosa?

Answer 17

E: adverse effects
A: beneficial effects
Lutein: no effects except positive in non-smokers with vit A

Question 18

How many people are affected by AMD? What is a recommended treatment?

Answer 18

20-50% >85 yoa; fruits, veggies, many antioxidants for 25% decreased progression; NOT lutein, zeaxanthin, omega-3 FAs

Question 19

What are three non-AMD age-related changes in vision?

Answer 19

Decreased contrast sensitivity (worse with AD), adaptation to change in light intensity, and depth perception

Question 20

What is a detached retina?

Answer 20

Neural retina detached from pigmented epithelium layer of retina leading to scotoma, floaters, flashes

Question 21

What is the pretectal area important for?

Answer 21

Consensual pupillary light reflex; input from RGCs, output to both CN3 nuc

Question 22

What is the superior colliculus involved in?

Answer 22

Reflexive head/eye movement to novel stimuli, and fixation to stimuli

Question 23

What is the pulvinar nuc of the thalamus?

Answer 23

Possible relay from retina to visual cortex, allowing “blind sight” in cortical blindness

Question 24

What does the suprachiasmatic nucleus produce, and what receptors does it have?

Answer 24

Produces vasoactive intestinal peptide (VIP), receptors for melatonin

Question 25

How does the foot activate visual cortex?

Answer 25

Lateral foot “vision acupoint” (sural, lateral planter nn) activates visual cortex in fMRI