Physiology and anatomy of the healthy retina and macula Flashcards
which 2 are the synaptic layers where connections between cells occur
outer plexiform layer
&
inner plexiform layer
which layer contains axons of retinal ganglion cells and where do these axons exit through
retinal nerve fibre layer
exits through the optic nerve head
which layer is between the RPE and choroidal circulation and what does it form inbetween these layers
bruch’s membrane
a permeable barrier
which 2 parts of the retina are supplied by the underlying choroidal circulation
outer retina
and
foveal avascular region
which 4 parts of the retina are a primary site of AMD and hence affected by age
choroid
bruch’s membrane
RPE
photoreceptors
which is the vascular layer between bruch’s membrane and the sclera and what vessel is it supplied by
choroid
supplied by the long and short ciliary artery which is derived from the ophthalmic artery
how many layers does the choroid consist of and what are they called
3
Haller layer
Sattler Layer
Choriocapillaris Layer
where is the Haller layer of the choroid found and what does it contain
closest to the sclera
contains large sized vessels
where is the Sattler layer of the choroid found and what does it contain
in the middle (between Haller and Choriocapillaris layers)
contains medium sized vessels
where is the Choriocapillaris layer of the choroid found and what does it contain
closest to bruch’s membrane
contains a dense network of fenestrated capillaries
what is the property of a fenestrated capillary layer
it doesn’t form a blood retinal barrier and molecules can freely move in and out of vessels
what is the major function of the choroid and at which part of the retina is it particularly important and why
to supply the outer retina with metabolites
and remove the waste products
the foveal avascular zone of the
macula
where the inner retinal circulation is absent
which part of the retina contains the greatest density of vessels of the widest diameter and why is this
The area beneath the macula
To supply optimal blood supply to this area of metabolic demand
what 3 things do ageing changes cause to the choroid
reduced thickness of the choroid
increased intercapillary spacing
a reduction in the
number and diameters of vessels
which 2 things of the choroid decrease with increasing age and what impact does this have
Choroidal blood flow and volume
impact of metabolites and removal of waste products from the retina
how many layers is bruch’s membrane composed of and what are they called
5
RPE basal lamina
Inner collagenous layer
Elastic layer
Outer collagenous layer
Choriocapillaris basal lamina
what type of structure does the collagen and elastic fibres form with bruch’s membrane
a sieve-like structure
Bruch’s membrane provides _______ and _______ for the RPE
support
and
anchorage
for the RPE
what 3 things pass from the choroidal circulation to the
outer retina via bruch’s membrane
and what passes in the opposite direction from the photoreceptors and RPE to reach the choroidal circulation
nutrients
oxygen
retinoids
metabolic waste products
which 2 disruptions causes an increased density in the strands of the sieve in the ageing of bruch’s membrane
Normal turnover of collagen and elastin fibrils is disrupted
Ageing of Bruch’s Membrane
- Chemical changes & _______ cross-linkage of ______.
- Normal turnover of _______ and ______ fibrils is disrupted, resulting in increased ________.
- Deposition of waste materials from ____ in ______ ______.
- Becomes more resistant to passage of materials between ____ and ______, hence more waste accumulates.
- ______ accumulation reduces ______ permeability.
- General age-related increase in the _______ from approx __ μm at birth, to _____ μm in the tenth decade of life.
Ageing of Bruch’s Membrane
- Chemical changes & increased cross-linkage of fibrils.
- Normal turnover of collagen and elastin fibrils is disrupted, resulting in increased density.
- Deposition of waste materials from RPE in inner layers.
- Becomes more resistant to passage of materials between RPE and choroid, hence more waste accumulates.
- Lipid accumulation reduces water permeability.
- General age-related increase in the thickness from approx 2 μm at birth, to 4-6 μm in the tenth decade of life.
Name the 3 ways the choroid changes and 1 way bruch’s membrane with age
Choroidal thickness decreases vs age
Capillary diameter decreases vs age
Capillary density decreases vs age
Bruch’s membrane thickness increases vs age
Retinal Pigment Epithelium is a _______ of hexagonal cells
Monolayer
what does the basement membrane of the RPE form
part of bruch’s membrane
The RPE ______ membrane faces the _____ retina, and numerous _______ envelop tips of the photoreceptor ______ segments.
Apical membrane faces the neural retina, and numerous
microvilli envelop tips of the photoreceptor outer segments.
which 4 things prevents a physically attached connection between the RPE and brunch’s membrane
osmotic pressure
fluid transport
interphotoreceptor matrix
presence of vitreous
what are the 6 major functions of the RPE
secretion of VEGF and PEDF
phagocytosis - processing the material and releasing in into the choroidal circulation
visual cycle - to regenerate pigment after it being bleached
glia - for exchange of potassium (k+)
epithelial transportation - of water, CI-, vit A and glucose
light absorption - which improves image quality
what does the ageing of the RPE result in
accumulation called lipofuscin
Due to incomplete degradation of phagocytosed outer segment material by the RPE
(which is also extruded into Bruch’s membrane)
as well as lipofuscin, what else accumulates in the RPE/Bruch’s membrane due to an ageing RPE and why
dead cells
as cell density declines with age which results in increased demand on remaining cells
By age 80, __% of RPE cytoplasmic space is filled with lipofuscin, compared to __% at age 40
By age 80, 90% of RPE cytoplasmic space filled with lipofuscin, compared to 8% at age 40
how is lipofuscin seen on Fundus Autoflorescence
bright glow
where is the peak density of lipofuscin seen
parafovea
highest ratio photoreceptor:RPE cells
where is the highest ratio of photoreceptor:RPE cells found
parafovea
in which 3 ways is lipofuscin toxic to the retina
can break down organelle membranes
increases photo-oxidative damage
mechanically damages cells
how are short wavelength sensitive cones different in morphology to long and medium wavelength sensitive cones of the photoreceptors
short wavelength sensitive cones have longer inner segments and smaller pedicles
long and medium wavelength sensitive cones have a similar morphology
which layer of the retina is the outer segment located and what does it contain
the photoreceptor layer
contains tightly packed membrane discs full of visual pigment
where on the retina is the max rod photoreceptor density found
18 deg eccentricity from the fovea
where on the retina is max cone density found
the fovea
what is the estimated number of rod photoreceptors found in the retina
110-125 million
what is the estimated number of cone photoreceptors found in the retina
6.3 - 6.8 million
which photoreceptor changes with age and how/by how much
rods
Rod density decreased by 30% in central 28.5°retina
Rod density decreased by __% in central ____ retina
Rod density decreased by 30% in central 28.5°retina
where is the initial loss of rods in the retina in the ageing eye and what happens to the remaining rods
in parafovea
outer segments of remaining rods expanded to fill gaps
what do bipolar cells synapse/convey signals from and to with in the retina
from photoreceptors and horizontal cells in the OPL to amacrine and RGCs in the IPL
how many types of bipolar cells are there in humans and what is 1 of them exclusive to
11
one is rod pathway specific
the remainder are cone pathway specific
which 2 pathways are bipolar cells involved with
OFF pathway (inhibited by light on receptive field centre; synapse in the outer part of IPL)
ON-pathway (excited by light on receptive field centre; synapse in the inner part of IPL)
name 2 types of bipolar cells and state the difference between the 2
Midget and Diffuse
Midget - synapse with few PRs
Diffuse - synapse with many PRs
what are the 2 types of bipolar cells which process short wavelength information
blue
&
giant bi-stratified
name the 2 interneurons
horizontal and amacrine cells
Horizontal cells synapse with _____________ and _______ ____ at the level of the ____, and connect with each other via ___ __________.
Horizontal cells synapse with photoreceptors and bipolar cells at the level of the OPL, and connect with each other via gap junctions.
how do horizontal and amacrine cells communicate information
laterally across the retina
horizontal and amacrine cells provide a feedback signal to ___________ and feedforward to ________ _____
horizontal and amacrine cells provide a feedback signal to photoreceptors and feedforward to bipolar cells
Amacrine cells synapse with ________ _____ and _____ at the level of the ____
Amacrine cells synapse with bipolar cells and RGCs at the level of the IPL
how many amacrine cells are there in humans
at least 25
name 3 types of retinal ganglion cells
midget cells
parasol cells
bistratified RGCs
how much of the retinal ganglion cells do midget cells make up
80%
which pathway do the midget RGCs start and what does this do
parvocellular pathway
they have small receptive fields/small dendritic feet (high SF sensitivity), show colour antagonism.
which RGC has high spatial frequency sensitivity
midget RGCs
how much of the retinal ganglion cells do the parasol cells make up
10%
which pathway do the parasol RGCs start and what does this do
magnocellular pathway
have larger receptive fields/large dendritic feet/trees (low SF sensitivity), respond strongly to transient/fast moving stimuli.
which RGC has low spatial frequency sensitivity
parasol RGCs
what type of info do RGC parasol cells process
red green colour opponent info
Bistratified RGCs form start of _________ pathway, and carry _____-_______ colour opponent information.
Bistratified RGCs form start of koniocellular pathway, and carry blue-yellow colour opponent information.
ON-bipolars synapse with?
ON RGCs (respond to light onset or light on dark background)
OFF-bipolars synapse with?
OFF-RGCs (respond to light offset or dark on light background)
the retinal nerve fibre layer contains ____ axons and blood vessels of ________ _________ circulation
the retinal nerve fibre layer contains RGC axons and blood vessels of inner retinal circulation
Retinal nerve fibre layer
Peripheral fibres are overlaid by more _______ fibres with __________ distance from the optic nerve head > ________ in thickness of RNFL
Peripheral fibres are overlaid by more central fibres with decreasing distance from the optic nerve head > increase in thickness of RNFL
where in the retina is the RNFL thickest at
the closer you get to the optic disc - it is thickest at the optic disc margin
Retinal nerve fibre layer
Fibres from the ________ region form the spindle-like ____________ bundle, which enters the __________ sector of the optic nerve head
Fibres from the macular region form the spindle-like papillomacular bundle, which enters the temporal sector of the optic nerve head
Retinal nerve fibre layer
Temporal fibres describe an ________ path to the _____ (around the papillomacular bundle), whilst nasal fibres take a more ______ route
Temporal fibres describe an arcuate path to the ONH (around the papillomacular bundle), whilst nasal fibres take a more direct route
How much % of retinal blood flow does the choroid receive and via which 2 arteries
65-85%
via the short and long posterior ciliary arteries
how much % of blood flows into the inner retinal layers and which vessel does this flow through
20-30%
flows into the retina through the central retinal artery from the ONH
how much of the population has a cilioretinal artery
15-20%
how many branches does the central retinal artery have
how many layers of the retina does it supply
what are the names of the capillaries and which layer of the retina do each of them supply
4
3 layers of capillaries
1) the radial peripapillary capillaries (RPCs) (in RNFL)
2) an inner layer of capillaries (in ganglion cell layer)
3) an outer layer of capillaries (runs from IPL to OPL)
which retinal layer are the radial peripapillary capillaries found
RNFL
which retinal layer are the inner layer of capillaries found
ganglion cell layer
which retinal layer are the outer layer of capillaries found
IPL to the OPL
what does the blood in the capillaries drain into
into venules and through the corresponding venous system to the central retinal vein
what are endothelial cells of the arterioles and capillaries formed by
tight junctions
what surrounds the arteriole and hence maintains it’s integrity
smooth muscle
what surrounds the capillaries and hence maintains it’s integrity
pericytes
what condition causes the death of smooth muscle on arterioles and pericytes on capillaries and what does this result in
diabetic retinopathy
reduces the integrity of the vessels
what is the size of the macula in mm and how much degrees of visual angle is it responsible for
6mm
15-20 degrees visual angle
what is the ganglion cell layer thickness at the macula area
more than 1 ganglion cell layer thick
what 4 components does the macula consist of
perifovea
parafovea
fovea
foveola
what is the foveola encircled by and where does this pass from and to
vascular arcades
passing from the optic nerve head, superior and inferior to the avascular zone
how large is the fovea in diameter and how much of the visual field does it represent
- 85mm diamater
5. 5 deg of visual field
how much of the visual field does the foveola represent
1°20’ of the visual field
which part of the retina has the maximum cone density and of how much
the foveola
200,000 cells per mm2
how are the foveal cones structured and why
rod-like in shape than peripheral cones due to greater PR density
Approximately ___% of retinal ganglion cells (RGCs) are within ___°of the foveola
Approximately 50% of retinal ganglion cells (RGCs) are within 13°of the foveola
what is the peak density of RGCs at 1mm eccentricity of the foveola
and what is the consequence of this
35,100 (the highest density)
Ratio of cones to retinal ganglion cells is lowest in the macular region
what is the estimated cone:RGC ratio at foveal centre and what does this allow for as a result
1:2 - cone:RGC
Allows for each foveal cone to contribute to ON- and OFFpathways.
Results in a low level of neural convergence (small
receptive field size) and allows high sampling density of
foveal cones throughout the visual pathway
what does the high sampling density of foveal cones throughout the visual pathway maximise
spatial acuity at fovea
at the foveola, how are all the cells placed and where about
all cells proximal to the photoreceptors are
displaced laterally
as seen in OCT - which retinal layers are thicker when adjacent to the foveal pit
GC and IPL layers
what is the thinnest part of the retina and why
Foveola
due to displacement of second and third order neurones,
achieved by elongation of cone cell axons (Henle Fibre
Layer).
what is the consequence of the foveola being the thinnest part of the retina
Central vision is not disturbed by the scattering of light prior to absorption by the photoreceptors
As a result of displacement of the cells from foveal pit,
parafoveal region has ganglion cells up to 6 layers deep
and is the thickest part of the retina.
which part of the retina is thickest and why
parafovea
As a result of displacement of the cells from foveal pit, it has ganglion cells up to 6 layers deep
what is the foveal region free from
blood vessel and capillary
what does the ring of macular vessels arise from
branches of the superior temporal and infero temporal arteries
what is the advantage of there being no blood vessels are the fovea
Central vision is not disturbed by the scattering of light by the blood vessels
what is the foveal avascular zone reliant on any why
the underlying choroidal circulation
for nourishment and waste removal
what does macular pigment consist of and what 2 things are they called
mixture of dietary xanthophyll carotenoids
lutein and zeaxanthin
which 2 places of the retina are the macular pigments lutein and zeaxanthin found
in cone axons of Henle Fibre Layer
and
interneurones of the inner plexiform layer
what happens to the macular pigment with eccentricity and what does become
the distribution drops off dramatically with increasing eccentricity
it becomes negligible at 5 deg eccentricity
what role does the macular pigment lutein and zeaxanthin have and what does this result in
a protective role, acting as an antioxidant, and filtering out short wavelength light - helping to protect against photo oxidative photo damage
Improves image quality - by selectively absorbing short wavelengths of light and reducing chromatic aberrations
