Retina

retina

innermost layer of the eye b/t the vitreous and choroid; continuous with epithelial layers of ciliary body

phototransduction

complex biochemical process by which the retina changes light energy into a signal that can be transmitted along neural pathways in the retina, exits the eye through the optic nerve, and transmitted to various parts of the brain for processing

ILM, NFL, GCL, IPL, INL, OPL, ONL, ELM, PRL, RPE

what are the layers of the retina from inner most to outer most?

photoreceptors

first order neurons; rods and cones; site of phototransduction

bipolar cells

second order neurons, transmit signals from photoreceptors to retinal ganglion cells; synapse with horizontal cells and photoreceptor at OPL, synapse with amacrine cells and ganglion cells at IPL

retinal ganglion cells

3rd order neurons; transmit signals from bipolar and amacrine cells to brain via optic nerve

horizontal cells

form connections with photoreceptors & bipolar cells; modify & integrate signals

amacrine cells

project to ganglion and bipolar cells; modify & integrate signals

Bruch’s membrane

acellular extracellular matrix that lies b/t the metabolically active RPE and choriocapillaris; transports H2O, ions, metabolites, nutrients, and waste products

B

elasticity

the ______ of Bruch’s membrane helps the eye withstand changes in IOP or choroidal blood flow

blood retinal barrier

Bruch’s membrane forms part of this to keep choroidal vessels from passing into the retina

increases

Bruch’s membrane _______ with age

thicker

Bruch’s membrane is _____ centrally than peripherally

basement membrane of RPE, inner collagenous zone, elastic fiber area, outer collagenous zone, basement membrane of choriocapillaris

what is the order of layers of bruch’s membrane from inner to outermost?

brittle

elastic fibers in Bruch’s membrane become more ______ over time due to degradation and calcification

increasing collagen synthesis

what may contribute to trapping and accumulation of cellular debris in the collagenous zones?

lipofuscin

incomplete lysosomal degradation of photoreceptor outer segments causes accumulation of this

drusen

deposits of lipids, proteins, and other cellular debris

retinal pigment epithelium

• outermost retinal layer

• monolayer of hexagonal cells

• cells do not divide

• barrier between choroid and neural retina

• contains many melanosomes

• C

columnar

what shape are RPE in the macula?

cuboidal

what shape are RPE near the ora serrata

highly folded

the basement membrane of the RPE is said to be what?

microvilli

apical surface of RPE has ______ that extend up into photoreceptors and envelop photoreceptor outer segment tips

4-6 million

how many RPE cells are there?

30-40

how many photoreceptors does each RPE cell interact with?

melanosomes

located in RPE, help absorb stray light and reduce light scatter

pigment, vitamin A metabolism, secrete growth factors, transport nutrients & metabolites, phagocytosis of photoreceptor outer discs, blood retinal barrier, sub retinal space helps balance ions/pH/fluids

what are functions of the RPE?

blood-retinal barrier

prevents components of blood plasma to enter the retina, which could impede light

no

are retinal capillaries fenestrated?

zonula occludens

located between RPE cells and form tight junctions and prevents movement of large molecules

constantly

how often are discs shed?

10%

during disc shedding ___ of photoreceptor volume is shed

circadian rhythm

what controls the timing of disc shedding

disc shedding

old discs are pinched off at the tips, captured by microvilli, and engulfed by RPE

RPE

what cells are the most active phagocytic cells in the entire body?

phagosomes

engulfed outer segments in membrane bound sac, fuse with lysosomes

phagolysosome

formed when phagosome fuses with lysosomes

decreases, accumulates, retinal degeneration

with age, lysosome function ______, lipofuscin ______, and this can lead to ___________________

hyper

lipofuscin is ____fluorescent

fundus flavimaculatus

autosomal recessive genetic disorder affecting RPE ability to remove cellular waste, which accumulates

lactate

byproduct of anaerobic metabolism

aquaporins

aid in the movement of water with Cl- and K-

glucose transporter

located on both apical and basal sides of RPE to maintain a steady supply of nutrients to photoreceptors

rods

• sensitive to low light (scotopic) conditions

• poor VA

• low spatial resolution

• absent color vision

• very sensitive to light

rhodopsin (OPN2)

what is the opsin type in rods?

cones

• sensitive to bright light (photopic) conditions

• good VA

• high spatial resolution

• color vision present

• less sensitive to light

S, M, L

what are the 3 types of opsins in cones?

498nm

what is the peak wavelength for rhodopsin/OPN2?

420nm

what is the peak wavelength for S/blue/OPN1SW?

531nm

what is the peak wavelength for M/green/OPN1MW?

588nm

what is the peak wavelength for L/red/OPN1LW?

fovea

where are cones most concentrated at?

tapered tip

what is the shape of cones?

blunt tip

what is the shape of rods?

around fovea, not at

where are rods concentrated at?

outersegment

part of photoreceptors that contains photo discs for converting light into neural signal

spherule

synaptic terminal for rods

G on left

pedicle

synaptic terminal for cones

G on right

outer nuclear layer

where are the cell body nuclei located for photoreceptors?

F

outer plexiform layer

where are the axon terminals located for photoreceptors?

G

outer segment, connecting cilium, inner segment, outer fiber, cell body, inner fiber

what are the parts of the photoreceptor from outermost to innermost?

inner segment

metabolic apparatus for photoreceptors, higher concentration of mitochondria

C

photopigment

opsonin + chromophore

chromophore

11-cis-retinal

opsin

determines the wavelength the pigment responds to

shape

chromophore changes _____ in response to opsin wavelength

vitamin A

where does 11-cis-retinal come from?

no

can the human body synthesize vitamin A?

all-trans-retinal

what does 11-cis-retinal transform into when activated?

interphotoreceptor retinoid binding proteins (IRBP)

moves all-trans-retinal into the RPE where it is converted to 11-cis-retinal

no

are there any intercellular junctions b/t the RPE and photoreceptors?

retinal detachment

caused by vitreous fluid getting into the retina and separating the photoreceptor from the RPE if a retinal tear or hole occurs?

outer plexiform layer

contains synapses of photoreceptors with bipolar cells and horizontal cells; common site for retinoschisis

retinoschisis

separation of retina at the OPL

inner nuclear layer

contains cell bodies of bipolar cells, horizontal cells, and amacrine cells

H

amacrine cells

processes are in IPL; synapses w/ bipolar cells, ganglion cells, and other amacrine cells; generally inhibitory (GABA/glycine)

horizontal cells

processes are in OPL; synapses with photoreceptors, bipolar cells, and other horizontal cells; releases both excitatory and inhibitory neurotransmitters

1

how many types of rod bipolar cells are there?

10

how many types of cone bipolar cells are there?

ON

__ bipolar cell synapses with cone photoreceptor, and its axons synapses to the ON ganglion cell

sublamina B of IPL

where do ON bipolar cells synapse with ON ganglion cells

depolarized

how are ON ganglion cells affected by light?

OFF

__ bipolar cell synapses with cone photoreceptor, and its axons synapses to the OFF ganglion cell

sublamina A of IPL

where do OFF bipolar cells synapse with OFF ganglion cells?

hyperpolarized

how are OFF ganglion cells affected by light?

A2 amacrine cell

what is responsible for relaying rod signals to both ON and OFF ganglion cells?

greater

there is ____ convergence of rods onto ganglion cells than cones

1:1

ratio for bipolar to cone cells at the fovea

inner plexiform layer

consists of synaptic connections made between bipolar cells, amacrine cells, and ganglion cells

I

ganglion cell layer

consists of retinal ganglion cells and displaced amacrine cells

J

parvo (p-type) ganglion cells

• 90% of RGCs

• axons terminate in parvocellular layers of LGN

• small cell bodies

• small receptive fields

• sensitive to high spatial frequency stimuli and color

• concentrated at fovea

magno (m-type) ganglion cells

• 5% of RGCs

• axons terminate in magnocellular layers of LGN

• large cell bodies

• large receptive fields

• sensitive to high temporal frequency stimuli

• carries luminance signals

• achromatic

• aka parasol cells

P1 cells

• aka midget ganglion cells

• most common type

• 1:1:1 cone: bipolar: ganglion

P2 cells

densely branched and compact dendritic trees that spread horizontally

konio (k-type) cells

• axons terminate in koniocellular layers of LGN

• large cell bodies

• large receptive fields

• carries blue-yellow color signals

• not well understood

intrinsically photosensitive retinal ganglion cells

• >1% of RGCs

• contain melanopsin

• can respond to light independently of and in absence of rods and cones

• non-image forming

• axons project to SCN and PON

nerve fiber layer

made up of 1-2 million ganglion cell axons that converge at optic disc; makes right angle turn to exit the eye; forms optic nerve which carries electrical impulses to various areas of the brain

K

internal limiting membrane

faces the vitreous, formed by basal aspect of Muller cells called Muller end feet and covered by basement membrane

L

external limiting membrane

not a true membrane, located between ONL and photoreceptor layer; formed by apex of Muller cells

E

neural glial cells

cells not directly involved in visual information processing; Muller cells, microglial cells, astrocytes; provide support, nutrients, waste removal, homeostasis, response to injury/inflammation/infection