Lecture 10: RPE Flashcards
what are the 10 layers of the retina
- Internal limiting membrane (ILM)
- Nerve fiber layer (NFL)
- Ganglion cell layer (GCL)
- Inner plexiform layer (IPL)
- Inner nuclear layer (INL)
- Outer plexiform layer (OPL)
- Outer nuclear layer (ONL)
- External limiting membrane (ELM)
- Photoreceptor layer (PR)
- Retinal Pigmented epithelium (RPE)
the RPE (10th layer of the retina) is what type of layer?
Monolayer of polarized cuboidal cells that separate photoreceptors from their underlying blood supply (choroid)
what are the 6 RPE functions
- Absorption of stray light
- Protection against toxic and oxidative damage
- Blood-retina-barrier
- Selective transport of substances to and from the retina
- Elimination of metabolic waste
- Processing Vitamin A metabolites
cell density is greatest where
fovea (~5000 cells/mm2)
peripherally (~2000 cells/mm2)
Are RPE and PRs are arranged apex- to-apex or base to base? what is this due to… and what is the result of this?
RPE and PRs are arranged apex- to-apex due to embryoloigcal development. Thus, a potential space, the subretinal space, is located between them.
what fills the subretinal space? what does it control?
Interphotreceptor matrix fills the space, is very strong, but no junctions. Controls trafficking of nutrients
RPE basement membrane is innermost layer of what?
Bruch’s membrane
RPE extends from
ora serrata (transitions from pigmented ciliary epithelium) to just before the optic disc
what is at the apical end of the RPE projecting between the OS of PRs
microvilli
Apical Membrane Specializations
Apical Na+/K+ ATPase pumps
Each RPE cell faces how many PRs
30-40 PRs
when do rods and cones shed?
- Rod discs are shed in the early morning
* Cone discs are shed during the evening
why is the RPE cell unique
it has Na+/K+ATPase pumps on its apical surface.
why is a Na+/K+ATPase pumps on its apical surface of RPE needed?
To regulate fluxes to keep the sensory retina (PR) adhered to the RPE
nutrient in
waste out
RPE does what to PR discs?
RPE digests, and recycles PR discs
what happens if the RPE can’t do its job?
If RPES can’t do its job it will dump the partially digested materials (hydrophobic) onto bruch’s membrane (DRUSEN), if stays within the cell
Drusen =
lipofuscin (increases with age)
what are the 10 ultrastructure features of the RPE
- apical microvilli
- lysosome
- junctional complex and terminal bar
- phagosomes
- melanin granules
- lipofuscin
- golgi apparatus
- basal infoldings
- RER and SER
- mitochondria
Ultrastructure function: apical microvilli
aids adhesion, phagocytosis, increased SA for metabolic exchange
Ultrastructure function: lysosome
contains hydrolytic enzymes which digest PRs
Ultrastructure function: junctional complex and terminal bar
component of blood- retinal barrier and ensures cell-cell adhesion
Ultrastructure function: phagosomes
contains phagocytosed PR segments
Ultrastructure function: melanin granules
absorbs excess visibile light and UV – reduces free radical damage
Ultrastructure function: lipofuscin
‘ageing pigment’, residual bodies from phagocytotic activity
Ultrastructure function: golgi
secretion and sulphation of GAGs
Ultrastructure function: basal infoldings
increase surface area for cell absorption and secretion
Ultrastructure function: RER/SER
protein and lipid synthesis
Ultrastructure function: mitochondria
large numbers indicate active ‘pumping’ epithelium
Lateral membrane (specialization of RPE): tight junction
blood - retina - barrier
RPE: blood -retina- barrier has tight junctions between what two cells
- Tight junctions (zonulae occludentes) between the RPE cells
- Tight junctions between the non-fenestrated endothelial cells of the retinal capillaries
TF: Retinitis pigmentosa (PR) is an autosomal recessive retinal dystrophy
F: An autosomal dominant retinal dystrophy
what is a progressive loss of RPE and PR function
Retinitis pigmentosa
RP Apoptosis:
rods and cones
Functional in peripheral retina
rods
functional in the Fovea
cones
“tunnel vision”
RP
(RP) Bone-spicule pattern:
RPE degenerates
and pigment migrates and deposits around blood vessels
RP treatment:
• To slow down progression
• High Doses of VitaminA (15000
IU/day)
• DHA, Omega 3, Vit C 1000mg, Lutein, Zeaxanthine (no solid evidence)
Congenital hypertrophy of the retinal pigmented epithelium (CHRPE) lesions are typically
solitary, flat, well-demarcated, hyperpigmented lesions of the retina, seen in a grouped configuration like “bear tracks”
Both solitary lesions and “bear tracks” are
benign
multiple, bilateral lesions can be associated with Gardner’s syndrome
an autosomal dominant disease which invariably results in colon cancer by the fifth decade of life
Retina:
window into CNS and Cardiovascular systems
retinal detachment (RD) usually separate at
RPE and PR
layer (as no intracellular junctions)
T/F: RPE remain attached to choroid and
can not be separated without difficulty
T: RPE remain attached to choroid and
can not be separated without difficulty
RD separates PR from their blood
supply, if not attached quickly what will happen to PR cells
if not attached quickly PR cells
will necrose and die
Argon laser is used to produce scar at
edges of RD to prevent
enlargement
and to reposition the layer
what can be used to reattach the retina and prevent fluid leakage in to breaks and subretinal space
Silicon oil (72% success rate) or gas temponade perfluropropane (87% success)
