retina and choroid

what are the 4 functions of the RPE

- metabolize/store vitamin A

- phagocytose outer segment discs

- produce interphotoreceptor matrix

- produce growth factor

how does the RPE breakdown outer segments of photoreceptors

lysosomes

if the outer segment discs aren't broken down sufficiently, what happens

the material accumulates as deposits of lipofuscin

what makes up the interphotoreceptor matrix

GAGs, proteoglycans

where is the interphotoreceptor matrix

apex of RPE, outer/inner segments of photoreceptors

what is the main function of the interphotoreceptor matrix

adhesive properties to hold the RPE/photoreceptors close together

what are the secondary functions for the interphotoreceptor matrix

-means of metabolite exchange between RPE/photoreceptors

-orienting photoreceptor segments toward the pupil

what would happen if the RPE didn't produce these growth factors

atrophy of capillaries that would further damage the retina

what is the function of the photoreceptors

phototransduction

what is the function of cone photoreceptors

photopic vision

what is photopic vision

vision in bright light, and the ability to recognize fine detail/discriminate colours

what is the function of rod photoreceptors

scotopic vision

what is scotopic vision

vision in dim light/darkness, poor fine detail recognition, gray shades

what is the function of horizontal cells

to integrate and regulate the input from several photoreceptors

what is meant by integrate/regulate input with horizontal cells

will amplify or diminish signals from photoreceptors

what is the function of bipolar cells

transmit information from photoreceptors to ganglion/amacrine cells

what is the function of amacrine cells

modify information from bipolar cells

what do ganglion cells form

optic nerve

where does the optic nerve course to

lateral geniculate nucleus

what is the function of the ganglion cells

bringing the retinal signal to the brain

how many functions do muller cells have

4

what are the 4 functions of muller cells

-provide structural support to neurons

-maintain extracellular pH

-recycle neurotransmitters

-make inner limiting membrane

how do muller cells maintain extracellular pH

absorbing metabolic waste products

what is the function of astrocytes in the retina

unknown, potentially similar to muller cells

astrocytes are only associated with one cell in the retina, which cell is it

ganglion cells

what is the function of microglial cells in the retina

immune response

what is the function of the blood retinal barrier

prevent components of blood from freely entering the retinal tissue

why is preventing blood entering the retina important

blood components will impede light and affect vision if leaked into the retina

what is the function of the retina

convert light energy into a neural signal

how does the retina carry the neural signal to the brain

optic nerve

how many functions does the RPE have

4

why does the RPE need to store vitamin A

the photoreceptors need vitamin A for phototransduction

how many outer segment discs does an RPE cell break down dialy

up to 2000

why would photoreceptor outer segments need to be oriented toward the pupil

for optimal light capture

what are the growth factors from the RPE intended for

maintenance of the choriocapillaris

how many factors contribute to the blood retinal barrier

3

what are the three factors that make up the blood retinal barrier

- RPE cell tight unctions

- central retinal artery tight junctions

- absence of fenestrations in the central retinal arteries

why do the RPE cells need to have tight junctions between them

to control what moves in/out of the retina

because of the tight junctions of the RPE cells, where do nutrients/waste pass through

through the RPE cells

where are the tight junctions in the central retinal arteries

between the capillary endothelial cells of the arteries

why are tight junctions necessary between the capillary endothelial cells of the central retinal arteries

to stop large molecules from leaving the retinal vessels

what are fenestrations

large holes within vessels that allow leakage of substances out

the absence of fenestrations in the central retinal artery capillaries does what

prevents large molecules from exiting the retinal vessels

why does the retina need a lot of nutrition

it's constantly using up energy

what processes in the retina are responsible for the need of constant energy

phototransduction, intracellular communication

where does phototransduction occur

photoreceptors

when is phototransduction happening

nearly constantly

the retina is an extensive network of ___ ___ ___

continual intracellular communication

what is the primary source of energy for the retina

glucose metabolism

how does glucose move from the capillaries into the retinal tissues

glucose transporters on the retinal capillaries and RPE

do the glucose transporters require energy?

no

what kind of diffusion does glucose use (simple/facilitated)

facilitated diffusion

what cells store glycogen in the retina

muller cells

what process do muller cells utilize to supply photoreceptors with glucose

glycolysis

where does aerobic glucose metabolism occur

photoreceptors

how much oxygen do photoreceptors use relative to other CNS neurons

3-4x more

what makes it possible for photoreceptors to use so much oxygen

choriocapillaris blood flow is significantly higher than in other tissues

what other energy producing pathway is found in the retina

pentose phosphate pathway

what does the pentose phosphate pathway produce

NADPH and pentoses

what resultant form the pentose phosphate pathway is needed for visual pigment regeneration

NADPH

why is visual pigment regeneration important

it's needed for phototransduction

what is the retina found between

the choroid and vitreous

the retina is the ___ ___ layer of the globe

inner neural

the outer retina is ___ to the choroid

inner

the inner retina is ___ to the choroid

outer

what is the anterior border of the retina

ora serrata

what is the posterior border of the retina

optic disc

what is another name for the anterior retina

far peripheral retina

what is another name for the central retina

posterior pole

what is the universal agreement on posterior pole boundaries

there isn't one, it's purely a clinical term

what does the posterior pole contain

macula, optic nerve, blood vessels out of optic nerve

where is the fovea found

in the macula

why does the fovea reflect light

it has it's own indentation

what is the point of highest visual acuity

fovea

what part of the retina is responsible for single vision

macula

what are the divisions of the optic nerve

optic disc, optic cup

what is the most anterior portion of the optic nerve

optic disc

where is the optic disc relative to the macula

nasal and superior

why is the optic disc orange

lamina cribrosa, choroidal vasculature

T/F: the optic disc is spherical

F

is the vertical or horizontal meridian of the optic disc larger

vertical is larger

what is the optic cup

a depression in the center of the nerve

what is the function of the optic cup

it's where the blood vessels enter/exit

what will cause a variation in optic cup size/depth

development and disease

what is the function of the equator

divide the globe into anterior/posterior poles

where is the midperiphery

between posterior pole and equator

where is the far periphery

equator to ora serrata

what is found in the mid periphery of the retina

vortex veins

how will we measure the size of the optic cup and disc clinically

compare how many times the cup will fit inside the disc vertically and horizontally

what will give us a more accurate measurement of the optic disc and cup

OCT

if the cup is really big, what has happened

we've lost axons of the ganglion cells

what are the three kinds of cells in the retina

epithelium, neurons, neuroglial cells

what cells are epithelial cells in the retina

retinal pigmented epithelium

what cells are neurons in the retina

photoreceptors, horizontal cells, bipolar cells, amacrine cells, ganglion cells

what cells are neuroglial cells in the retina

muller cells, microglial cells, astrocytes

what characteristic defines the central retina

2+ layers of ganglion cells and xanthophyll pigments

the peripheral RPE becomes what at the ora serrata

pigmented epithelium of the ciliary body

what happens to the nuclear layers of the peripheral retina at the ora serrata

they merge with the plexiform layers

what does the internal limiting membrane of the peripheral retina become at the ora serrata

inner basement membrane of the ciliary body

what region of the retina contains cones

central retina