Retina Flashcards
What is the nervous coat of the orbit called?
Retina
What must light pass through to reach retina? 4
cornea, aqueous humor, lense, vitreous body
What is the fovea centralis?
central point of retina with only cones
What does the abundance of cones in fovea do?
gives high level of visual aquity
Maculua lutea
Yellow area surrounding fovea
what gives maculua lutea its yellow color?
Accumulation of lutein and zeaxanthin, carotenoids
what do the carotinoids of the maculea do?
antioxidant activity, absorb excess blue/ultraviolet light.
why is there a blind spot?
The optic dist is where axons and central artery exit the orbit, there are no receptors.
What supplies blood to retina?
Brance of internal carotid, the central artery.
What surface of retina does central artery exit onto?
Central artery exits onto the inner surface of retina
What are the 4 retinal layers?
RPE retinal pigmented epithelium, Photo receptors, neural cells and ganglion cells
What do photo receptors do?
absorb visible light
What do neural cells due?
they integrate light information,
What form are neural cells?
bipolar, (horizontal and amarcrine)
Job of ganglion cells?
project visual information to thalamus, superior colliculus and more, their axon leaves the eye
What does the outer layer of rods and cones contain?
stacks of pigmented disks.
Pigmented disks in rods?
rhodopsin
Pigmented disks in cones?
iodopsin
what does the inner segment of photoreceptors, the part with the nucleus contain?
synaptic terminal that releases glutamate
Visable light is part of whats frequency spectrum
electromagnetic radiation
where are the pigments in photoreceptors located?
inside vescular disks on the terminal end
What spectrum of visable light do pigments respond to?
450 - 700 nm
What happens to photo receptor upon exposure to light?
Hyperpolarization that inhibits release of glutamate
What channels close to hyperpolarize cell?
Na and Ca++
what type of messenger signal closes the channels to cause hyperpolarization?
Opsin activates Phosphodiesterase PDE via a transducen
What type of messenger is transducen?
G protein
Light converts retinal how?
from cis retinal to trans retinol
Photopic
vision in bright light, low sensitivity
Scotopic
vision in dim ligh, highly sensitivity, night vision
What receptor is photopic?
cones, best in bright light
What receptor is scotopic?
rods, good for ight vision
What receptor gives the best acuity?
cones, because they are concentrated in fovea
what gives best spacial resolution, ie acuity?
cones
What receptor is achromatic?
cones,, color vision through 3 pigmented cells.
What receptors are more sensitive to scattered light?
rods, good for ight vision
What receptor is better at detecting visual motion?
rods.
Where are cones in the retina?
everywhere but they are most abundant in the fovea
Where are rods in the retina?
The are not in the fovea but are extreamly abundant everywhere else.
Why would the fovea have the most cones?
because it is the center of the visual field. So wants the best visual aquity
How are cells arranged in the fovea?
The shallower cells, the ganglion and bipolar cells are pressed away to the side allowing light more direct acess to the cones for increased acuity
Why is it good that the photo receptors are so deep in the retina?
IT puts them closest to the choroid body
Why do rods and cones need to be near blood supply, choroid body?
because pigment turnover requires lots of oxygen
How does light get past the ganglion and bipolar cells?
light passes through them, they refract just like aqueous humor
What is the layer deep to the photoreceptors?
retinal pigment epithelium RPE
What are the 5 jobs of the RPE?
Visual acuity, antioxidant, maintain photoreceptor excitability, nutrients provider, phagocytosis of cell debries
How does RPE effect visual acuity?
limits reflection of light back to receptors after the first pass, prevents blurred image
Why would RPE absorbe blue light?
blue light increases free radical formation in retinal cells
what brings retinol to photoreceptors?
RPE retinal pigmented epithelium, Photo receptors, neural cells and ganglion cells
what would deficient uptake of membrane fragments cause?
separation of receptors from choroid.
if receptors separate from RPE, what would happen?
anoxia and cell death
why is fovea avascular?
improved acuity without vascular interference
how does waste and water get transported from extracellular space at fovea to choroid?
Membrain transporters in the RPE
Why is retinal detachment relatively easy?
Attachment of REP to photoreceptors is unstable, there is nothing physically keeping them together.
What can cause retinal detachment, 2?
Buildup of cellular waste under the retina or leaking blood vessels under RPE
What is detached retina called?
macular degeneration
What does optic nerve consist of? 3
Axons of ganglion cells, GLIAL cells, central artery and vein
Why should optic nerve be called tract?
Because it has menegies just like the CNS
What type of CNS glia does optic nerve have?
Oligodendrocytes and astrocytes
oligodendrocytes do what?
myleinate axons
astrocytes do what?
surround cell bodies and dendrites, and also contract blood vessels.
Papilledema
increased CSF pressure that limits venous return from retina causing edema under optic disc.
how to idea papilledema?
blurred disk margin when viewed with opthalmoscope
What does papilledema do in additon to edema under optic disk?
Expaned CSF space around CN II, More veins in eye, axoplasmic stasis of ganglion cells.
why do we not notice our blind spot?
binocular vision, info within blind spot is interpolated from adjacent areas of retina during eye movements or by visual cerebral cortex activty.
