Vision Physio & Clinical Flashcards
What benefits do convergence and divergence have? at what cost?
Conv: increased sensitivity, decreased acuity (i.e. rods)
Div: decreased sensitivity, increased acuity (i.e. cones, and projections from occ cx)
What are M cells and P cells?
Magno- and parvo-cellular RGCs. M: large receptive field, sensitive, for peripheral/night vision. P: small receptive field, good acuity, central/macular vision
To which cells does center-surround antagonism apply?
Bipolar neurons, RGCs, LGN
What are ON and OFF cells?
ON: light in center excites neuron, dark inhibits
OFF: light in center inhibits, dark excites
How do center and surround cells affect bipolar cell?
Center: direct to bipolar cell
Surround: via inhibitory horizontal cell (lateral inhibition)
What is the function of ocular dominance columns? Ocular orientation columns? Blob channels?
ODC: depth perception
OOC: where/mvmt and what/shape
Blob: color
What is amblyopia?
“Lazy eye” that affects ocular dominance columns to avoid diplopia; causes loss depth/spatial perception
What is strabismus?
Misaligned eyes due to muscle problems, CN problems, etc. May cause diplopia, loss of depth/spatial perception
What are treatment options for amblyopia?
Patch good eye and force use of bad eye, blur good eye with cholinergic blockers
Describe the M-channel/movement pathway.
M-RGC (periphery retina) -> certain LGN layers -> certain V1 areas (OOC) -> certain visual assc areas -> post par cx
Describe the P-channel/shape pathway.
P-RGC (central retina) -> certain LGN layers -> certain V1 areas (OOC) -> certain visual assc areas -> fusiform gyrus
What deficit occurs with lesion of fusiform gyrus?
Inability to recognize familiar faces, even your own
Describe the blob channel/color pathway.
Non-P/M-RGC (central) -> certain LGN layers -> certain V1 areas -> certain assc cx areas -> fusiform gyrus
What is diabetic retinopathy? How does it affect type 1 and type 2 differently? What are signs of it?
Type 1: nearly all have some
2: Most (60%) have some
Microvessel problems lead to micro-aneurysms, -hemorrhages, vessel proliferation
What are the clinical features and progression of retinitis pigmentosa?
Slowly progressive photoreceptor degen causing rod loss, tunnel vision, then cone loss and retinal degeneration
How does light cause a neural signal?
Photopigments isomerize, increase cGMP PDE to decrease cGMP, close cGMP-gated Na channels -> hyperpolarize by decreasing glutamate release
How do vitamins A and E and lutein affect retinitis pigmentosa?
E: adverse effects
A: beneficial effects
Lutein: no effects except positive in non-smokers with vit A
How many people are affected by AMD? What is a recommended treatment?
20-50% >85 yoa; fruits, veggies, many antioxidants for 25% decreased progression; NOT lutein, zeaxanthin, omega-3 FAs
What are three non-AMD age-related changes in vision?
Decreased contrast sensitivity (worse with AD), adaptation to change in light intensity, and depth perception
What is a detached retina?
Neural retina detached from pigmented epithelium layer of retina leading to scotoma, floaters, flashes
What is the pretectal area important for?
Consensual pupillary light reflex; input from RGCs, output to both CN3 nuc
What is the superior colliculus involved in?
Reflexive head/eye movement to novel stimuli, and fixation to stimuli
What is the pulvinar nuc of the thalamus?
Possible relay from retina to visual cortex, allowing “blind sight” in cortical blindness
What does the suprachiasmatic nucleus produce, and what receptors does it have?
Produces vasoactive intestinal peptide (VIP), receptors for melatonin
How does the foot activate visual cortex?
Lateral foot “vision acupoint” (sural, lateral planter nn) activates visual cortex in fMRI
