Retina and retinal pigment epithelium Flashcards
What layer is the retina in relation to the three coats of the eye?
it is the innermost of the 3 coats
What are the 2 primary layers that the retina consists of?
- Inner neurosensory retina
- Outer simple epithelium: retinal pigment epithelium (RPE)
To what can the 2 primary layers of the retina (inner neurosesory retina and RPE) be traced embryologically?
inner and outer layers of the invaginated optic cup
In adults, what are the 2 primary layers of the retina continuous with anteriorly?
epithelial layers over the ciliary processes and posterior iris surface
What lies between the neural retina and RPE?
a potential space, the subretinal space, across which the two layers must adhere
At what points are the only attachments of the neural retina?
anterior termination the ora serrata, and margins of the optic nerve head
Where does detachment of the retina occur?
between the neural retina and RPE
What does the micrograph show?
the human retina
acronyms:
- NFL = nerve fibre layer
- GCL = ganglion cell layer
- IPL = inner plexiform layer
- INL = inner nuclear layer
- OPL = outer plexiform layer
- ONL = outer nuclear layer
- INS = inner segments
- OS = outer segment
- RPE = retinal pigment epithelium
- CC= choriocapillaries
What happens in retinal detachment?
the neural retina separates from the retinal pigment epithelium (RPE) thus reopening the embryonic intraretinal space or optic ventricle (analogous to ventricles of the brain), known in the adult as the subretinal space
What tends to fill the opened subretinal space in retinal detachment?
proteinaceous exudate
What 3 things normally maintain adhesion of the neural layer and RPE?
- negative pressure
- viscous proteoglycans in the subretinal spce
- electrostatic forces
What binds the retina a) externally and b) on its internal aspect?
- a) externally: Bruch’s membrane
- b) internally: vitreous
What is the relation of the retina to the optic nerve?
the retina is continuous with the optic nerve posteriorly, the site of exit of ganglion cell axons from the eye
What are the 6 key topographical regions of the retina?
- Posterior pole or central retina (area centralis)
- Macula lutea (fovea)
- Fovea centralis (foveola)
- Optic disc
- Peripheral retina
- Ora serrata
What is the posterior pole or central retina known as anatomically?
area centralis
What is the posterior pole or central retina?
5-6mm diameter circular zone of retina situated between the superior and inferior temporal arteries
Which photoreceptors dominate the posterior pole or central retina?
cones
What characterises the posterior pole or central retina histologically?
the presence of more than a single layer of ganglion cell bodies
What is the anatomical term for the macula lutea region of the retina?
fovea
What is the macula lutea?
a 1.5mm diameter area in the posterior pole, 3mm lateral to the optic disc
What colour is the macula lutea and why?
partly yellow
result of xanthophyll carotenoid pigments (zexanthin and lutein) in the cone axons
What may be the purpose of the colour of the macula lutea?
This may serve to act as a short wavelength filter protecting against UV irradiation
What is the anatomical term for the fovea centralis?
foveola
What is the fovea centralis?
central 0.35mm wide zone in the macula, consisting of a depression surrounded by slightly thickened margins
What is the distribution of photoreceptors like in the fovea centralis (foveola)?
cone photoreceptors are concentrated here at maximum density to the exclusion of rods
What is the arrangement of the inner retinal layers in the margins of the pit in the fovea centralis (foveola)?
the inner retinal layers in the margins of the pit are displaced laterally
What is the name of the pit in the fovea centralis (foveola)?
clivus
How does the foveal retina receive nutritional support?
it is avascular, relies wholly on the choriocapillaris
What is the location of the optic disc?
lies 3mm medial to the centre of the macula (fovea)
Why is the optic disc a blind spot?
there are no normal retina layers in this zone as ganglion cell axons from the retina pierce the sclera to enter the optic nerve
What is the diameter of the optic nerve and what happens at its edges?
diameter 1.8mm
slightly raised rim
What is the arrangement of blood vessels at the optic disc?
the central retinal vessels emerge at the centre of the optic disc, pass over the rim, and radiate out to supply the retina
the vein usually lies lateral to the artery
What is the usual relation of the central retinal vein to the artery at the optic disc?
the vein usually lies lateral to the artery
What is the peripheral retina?
the remainder of the retina outside the posterior pole
What is the distance from the optic disc to the ora serrata temporally vs nasally?
- temporally: 23-24mm
- nasally: 18.5mm
What is the thickness of the peripheral retina?
110-140 µm
What are the photoreceptors and neural layers like in the peripheral retina?
rich in rods
only one layer of ganglion cell bodies
What is the ora serrata?
the scalloped or dentate anterior margin of the sensory retina
at this transition zone, the neuroretina is continuous with the columnar non-pigmented epithelial cells of he pars plana
What cells is the neuroretina continuous with at the ora serrata?
the columnar non-pigmented epithelial cells of the pars plana
How does the relation of the ora serrata to the limbus compare temporal side vs nasal side?
the ora serrata is approx. 1mm closer to the limbus on the nasal than on the temporal side
How is the retina divided for descriptive purposes only?
nasal and temporal halves, divided by a vertical line through the fovea
What regions of the retina can the optic nerve head be used to help describe?
used as central point to describe supero- and inferonasal and supero- and inferotemporal quadrants
What is the area of the retina?
1250mm2
What is the range in thickness of the retina?
from 100 μm (periphery) to 230 μm (near the optic nerve head)
What is the retinal pigment epithelium (RPE)?
continuous monolayer of cuboidal/columnar epithelial cells, which extends from the margins of the optic nerve head to the ora serrata where it is continuous with the pigment epithelium of the pars plana
Which type of cells is the RPE composed of?
monolayer of cuboidal/columnar epithelial cells
Between which regions does the retinal pigment epithelium extend?
from the margins of the optic nerve head to the ora serrata
What structure is the RPE continuous with at the ora serrata?
pigment epithelium of the pars plana
What are 6 of the functions of the RPE?
- Maintaining adhesion of the neurosensory retina
- Providing a selectively permeable barrier between the choroid and neurosensory retina
- Phagocytosis of rod and (to a lesser extent) cone outer segments
- Synthesis of the interphotoreceptor matrix
- Absorption of light and reduction of light scatter within the eye, improving image resolution
- Transport + storage of metabolites and vitamins (especially vitamin A)
What is the embryological origin of the RPE?
neuroectoderm
What causes RPE cells to vary in shape and size and what typical pattern of variation do they follow?
vary depending on age and location
more columnar in the central retina (14 μm tall, 10 μm wide) and more flattened (10–14 μm tall, 60 μm wide) in the peripheral retina
What membrane/cells is intimately associated with the photoreceptor outer segments of the RPE?
basal aspect of the cells on Bruch’s membrane and their apical surface
What is the organisation of epithelial cells within the RPE when examined en face?
highly organised hexagonal pattern of homogenously sized cells
What is the number of RPE cells per eye?
varies 4.2 -6.1 million
Label the following on the diagram of the RPE:
- apical microvilli
- lysosomes
- junctional complex and laminal bar
- melanin granules
- lipofuscin
- Golgi apparatus
- basal infoldings
- rough and smooth endoplasmic reticulum
- mitochondria
What are 9 key features of the RPE to be aware of?
- apical microvilli
- lysosomes
- junctional complex and laminal bar
- melanin granules
- lipofuscin
- Golgi apparatus
- basal infoldings
- rough and smooth endoplasmic reticulum
- mitochondria
What is the function of the apical microvilli of the RPE?
aids adhesion, phagocytosis, increased surfaec area of metabolic exchange