1. 12/07/2010EC. MuezA 1
Anatomy of the Retina
Presenter; Muez A. (1st year
Ophthalmology Resident)
Moderator; Dr Demoze (Consultant
vitreoretinal Surgeon)
3. Introduction
Inner posterior 2/3rd of the eye ball
Continuous posteriorly as optic nerve,
anteriorly with the ciliary body
Bordered by the vitreous internally & the Bruch’s
membrane externally
It has pigment epithelium and neural layer
Surface area of about 266 mm2
Thickest in the papillomacular bundle near the optic
nerve (0.23 mm)
thinnest in the foveola (0.10 mm) and ora
serrata (0.11 mm).
Site of transformation of light energy into a neural
signal.
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4. Gross anatomy
The major landmarks of the retina
The area centralis
The peripheral retina
The optic disc
The retinal blood vessels
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5. Central Retina
Rich in cones, has more ganglion cells per area than elsewhere
Small portion of the entire retina.
1. Foveola
2. Fovea
3. Para fovea
4. Perifovea
5. Macula
Clinical function
• Fine visual acuity
• Photopic vision
• Stereopsis‘
• Color vision
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6. Macula
Demarcated by superior and inferior temporal arterial arcuate
Dark area in the central retina
Elliptical shape horizontally
Average diameter of about 5.5 mm/3.5DD
15-18° of visual field
Protects central vision by following characteristics;
Highly pigmented tall epithelial cells of RPE(highest pigmentation )
reduce scattering of light
The choroidal capillary bed also is thickest in the macula
Highest concentration of xanthophyll pigments
Act as filters, absorbs short wavelength visible light to reduce
chromatic aberration
Antioxidant effect
Protective role against UVR damage.
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8. FOVEA
center of macula
Diameter of 1.5-1.85mm/1DD
Represents 5° of the visual field
Central depression foveola
The inner nuclear layer and ganglion cell layer are
displaced laterally and accumulate on the curved walls of
the fovea called Clivus
The fovea has the highest concentration of cones
(199,000-300,000 cones/mm)
The photoreceptor fibers(cones) become longer as they
deviate away from the center; these fibers are called
Henle’s fibers
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9. Foveola
Central depression in the fovea
1° of visual field
0.35mm in D/0.3-0.4DD
Six layers present in the foveola
Internal limiting membrane
Henle’s fiber layers
ONL
External limiting membrane
Photoreceptor layers
RPE
form sharpest vision and steoropsis
Umbo (Center of foveola) corresponds to light reflex
Foveal reflex is due to the parabolic shape formed
by the clivus.
Loss of foveal reflux implies disruption of neural layers
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10. Clinical correlates;
• Lack of blood vessels and neural tissue in foveola allows
light to pass unobstructed into the photoreceptor outer segment
Chronic retinal oedema may result in the deposition of hard exudates
around the fovea in the layer of Henle with a macular star
configuration
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12. Rods reduces and are replaced by malformed cones
The nuclear layers merge with the plexiform layers,
Finally, neural retina becomes a single layer of
irregular columnar cells
that continue as the nonpigmented epithelium of the ciliary
body.
TheRPE is continuous with the outer pigmented epithelium
of the ciliary body,
the internal limiting membrane continues as the internal
limiting membrane of the ciliary body.
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13. Ora Serrata
The ora serrata is the boundary between the retina and the
pars plana.
A firm attachment between the retina and vitreous
Its distance from the Schwalbe line is between 5.75 mm
nasally and 6.50 mm temporally.
In myopia, this distance is greater; in hyperopia, it is
shorter.
The Bruch membrane extends anteriorly, beyond
the ora serrata, but is modified because there is no
choriocapillaris in the ciliary body
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14. Topographically, the ora serrata is relatively smooth
temporally and serrated nasally.
Retinal blood vessels end in loops before reaching the
ora serrata.
The ora serrata is in a watershed zone between the
anterior and posterior vascular systems
peripheral retinal degeneration is relatively common.
The photoreceptors are malformed, and the overlying
retina frequently appears cystic (Blessing Iwanoff cysts)
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17. PERIPHERAL RETINAL DEGENERATION
Cystic spaces and atrophied areas often are
found in peripheral retina
and their incidence increases with age.
poor blood supply in the extreme retinal periphery.
others might predispose the affected dilated fundus
examinations.
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19. cont….
The number of nerve fibers appears to be positively
correlated with the size of the optic nerve head
larger discs have relatively more fibers than
smaller discs
Smaller discs may demonstrate optic nerve head
crowding.
Fiber number decreases with age.
The pale-yellow or salmon color of the optic disc
is a combination of the scleral lamina cribrosa and
the capillary network.
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21. Optic DISC ASSESSMENT
The color of the disc
configuration and depth of the physiologic cup
cup-to-disc ratio
appearance of the rim tissue
disc borders are assessed during an ocular
health examination.
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24. Retinal pigment epithelium
The first retinal layer to be formed (3-4
month)
the earliest pigmentation evident in the
embryo
one cell thick, the cells are cuboidal to
columnar in shape
the base of each cell is external toward the
developing choroid
the apex internal toward the inner layer of
the optic cup
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25. The neural retina
week 7, cell migration occurs, forming the inner and
outer neuroblastic layers
Outer neuroblastic layer differentiates to photo
receptor cells,bipollar cells and horizontal cells (outer
plexiform)
Inner neuroblastic layer differentiates to Ganglion
cell, amacrine, and Müller cells (inner plexiform
layer)
The photoreceptor cells are the last cells of neural
retina to differentiate (5th month)
Differentiation of the neural retinal cells begins in
central retina and proceeds to the periphery
The Muller cells forms the internal limiting membrane
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26. 6 months dense accumulation of nuclei in the macular
area makes this region thicker than the rest of the
retina
the ganglion axons from the periphery
take an arched route above and below the
macular area to reach the nerve head.
Foveal development consists of three stages
(1) displacement of inner retinal components to
form the depression;
(2) migration of photoreceptors toward the center,
which increases cone packing
(3) maturation of the photoreceptors.
At 7month the ganglion and inner nuclear layer cells
begin to move to the periphery of the macula.
By 4 months postpartum, both these layers are
displaced
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27. The foveal depression continues to deepen until about age 15
months
The foveola, the retinal area of sharpest visual acuity, is the
last to reach maturity.
migration of the cones centrally, increasing cone density.
The cone inner fibers elongate and adopt an oblique
orientation
(forming Henle’s fiber layer) in order to synapse with the
cells of the inner nuclear layer, which have been displaced
to the sloping walls
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28. CLINICAL COMMENT: COLOBOMA
Incomplete closure of the
optic fissure may affect
The developing optic cup
or stalk and the adult
derivations of these
structures,
resulting in an inferior nasal
defect in the optic disc,
retina, ciliary body, or iris.
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31. 1.Retinal pigment Epithelium
4-8 million cells firmly attached to its basal
lamina
Single cell thick and consists of pigmented
hexagonal cells
Columnar in the area of the posterior pole
densely pigmented in the macular area.
Larger and more cuboidal less pigmented as
the layer nears the ora serrata,
Phagocytic cells
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32. Contain numerous melanosomes,pigment granules
Pigment density differs in various parts of the retina
Densest at the macula and at the equator
decreased transmission of choroidal fluorescence
observed during fundus fluorescein angiography
Lipofuscin granules arise from the discs of
photoreceptor outer segments and represent
residual bodies arising from phagosomal
activity
This so-called wear-and-tear pigment
less electron dense than the melanosomes
increases gradually with age.
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33. Other material are excreted beneath the basal
lamina of the RPE
formation of drusen( accumulations of this
extracellular material)
can vary in size and are commonly classified by
their funduscopic appearance as either hard or
soft.
located between the basement membrane of the
RPE cells and the inner collagenous zone of the
Bruch membrane.
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34. RPE - Cell Surfaces characteristics
Clinical significances;
No specialized junctional complex between RPE
and photoreceptors- loosely adhered
Potential space exists (subretinal space)- prone for
RD)
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Apical surface
• Has microvillous processes- Increases Surface
area
• Interdigitate with outer segments of
photoreceptor cells
• Contains melanin granules – more dense in
macular region
1.Apical surface –inner surface
2.Paracellular (lateral) surface-intercellular surfaces
3.Basal surface – outer surface
35. Paracellular surface;
Contains tight junction( Zonula Occluden & adheran, gap junctions)
Junctional complex form blood-retinal barrier
Maintains retinal homeostasis and prevents from toxic damages
35
Basal surface;
• Attached to its basal
lamina, the lamina vitrea
of Bruch's membrane.
• Nutrients from
choriocapillaries difusess
to RPE through basal
lamina
36. Sensory neural retina
Transparent layer
Contains 3 basic cell types
photoreceptor cells
Rods and cons……120 million vs 6 million respectively
Constitutes the outer nuclear layer and the outer plexiform layer.
Neuronal cells
Bipolar cells
Horizontal cells 1st order neurons
Amacrine cells
Ganglion cells 2nd order neurons
Glial cells
Muller cells
Astrocytes
Microglial cells
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37. Müller cells are large neuroglial cells that extend much of
the retina.
Supportive role, and providing structure
Fill in most of the space of the retina not occupied by
neuronal elements
Ensheathe dendritic processes within the synaptic
layers,
providing insulation from electrical and chemical
activation,
Involved in glucose metabolism by synthesizing and
storing glycogen
Buffer in regulating concentrations of potassium ions
(K+),GABA, and glutamate in the extracellular space.
Apex in the photoreceptor layer, basal aspect is at the
inner retinal surface
Apical villi, fiber baskets (of Schultze), terminate
between the inner segments of the photoreceptors.
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39. Microglial cells are wandering phagocytic cells
found anywhere in the retina.
increases in response to tissue inflammation and
injury.
Astrocytes star-shaped fibrous cells
found in inner retina, usually in the nerve fiber and
ganglion cell layers.
perivascular cells form an irregular supportive network
encircles nerve fibers and retinal capillaries.
contribute to the internal limiting membrane
Amacrine cells
No axons.
Stimulated by the Bipolar cells & then they excite
the Ganglion cells
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40. Bipolar cells
First order neuron in the visual pathway.
Its dendrite synapses with photoreceptor and horizontal
cells
Axon synapses with ganglion and amacrine cells
Eleven types of bipolar cells have been classified on the
basis of morphology, physiology, and dendritic contacts
with photoreceptors
Horizontal Cells
They have one long & several short processes.
Inhibitory function by releasing GABA.
highest concentration in fovea
Modulate and transform visual information received
from the photoreceptors
Have a role in sharpening contrast
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41. Ganglion cells
2nd order neurons
W cells project to the midbrain, carrying information
for the pupillary response and reflexive eye
movements.
Y cells project to the lateral geniculate body, with
some having collateral branches that travel to the
midbrain, perhaps with pupillary information
X cells primarily respond in visual discrimination and
project to the lateral geniculate body
P ganglion cells ; color vision stereopsis
M ganglion cells ; rapidly to moving or changing stimuli.
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42. 2. Photoreceptors
CONES
4_8 million cells
density is maximum at
fovea (199 000
cones/mm2)
-minimum density-
periphery
light sensitive molecule
Iodopsin ( color vision-
photopic vision)
( 3 types of iodopsin
trichromatic pigments
1. S wavelength cones-
440nm blue light)
2.M wavelenght cone-
540nm green
3. L wavelenght cone-
577nm red
RODES
100-130 million cells
maximum density in 20°(3mm) from
the fovea(160,000 rods/mm2)
rod-free at the fovea ; 0.35 mm
minimum density periphery
light sensitive molecule- rhodopsin (
night vision- scotopic vision)
rhodopsin is sensitive to blue-green
light- 493nm
Main for white and black
Clinical notes
Mutation of rhodopsin in retinitis
pigmentosa
With advanced of age there is
progressive loss of photoreceptors
(rods are affected more than
cone)
poor night vision in elderly
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43. Morphology of Photoreceptors
Rods and cones have six main parts
1. The outer segment, containing the visual
pigment molecules for the conversion of
light into a neural signal
2. A connecting stalk, the
cilium(cytoplasmic isthmus)
3. The inner segment, containing the
metabolic apparatus;
4. The outer fiber;
5. The cell body- forms outer
nucleated layers
6. The inner fiber, which ends in a synaptic
terminal outer plexiform layer
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45. the outer segments of the rods and cones
difference.
Rod discs are not attached to the cell membrane
Cone discs are attached to the cell membrane
renewed by membranous replacement.
cone synaptic body, or pedicle, is more complex
than the rod spherule.
Cone pedicles synapse with other rods and cones
as well as with horizontal and bipolar cell
processes.
Foveal cones have cylindrical inner segments
similar to rods but otherwise are cytologically
identical to extrafoveal cones.
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46. The Rods
The most light sensitive cells
Components of disc membranes are produced in
the inner segment
Discs contain 90% of the visual pigment remaining is
scattered on plasma membrane.
move along the connecting stalk to be discs
at the outer segment
The discs gradually displaced outward and form new discs
and sloughed off and phagocytosed
the rod outer segment renewal system
shed regularly, with mostly occurring in the early morning.
The inner fiber extends from the cell body and terminates in
structure called a spherule
The spherule forming a synaptic complex with
bipolar dendrites and horizontal cell
Rods release the neurotransmitter glutamate
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47. Cones
The cone outer segment is
shorter
Don’t not reach the RPE
layer.
Tubular processes protrude
from the apical surface
of the epithelial cell to
surround the cone outer
segment
Cone at periphery is short
but in central fovea it is
tall and resembles rod
As with rods, cones use
glutamate for
aneurotransmitter.
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48. The photoreceptor cell layer and the RPE layer.
Passive forces
intraocular pressure (IOP)
osmotic pressure
fluid transport across the RPE
presence of the vitreous
physical closeness between the two entities
RPE microvilli and the rod and cone outer
segments
interphotoreceptor matrix (IPM )
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49. Retinal detachment
Separation RPE cells and the photoreceptors
because no intercellular junctions join these cells.
The RPE cells remain attached the choroid
separates the photoreceptors from their blood supply,
the layers are not repositioned quickly, the affected area
will necrose.
Anargon laser often is used to photocoagulate the edges
of the detachment, producing scar tissue.
This photocoagulation prevents the detachment from
enlarging and facilitates the repositioning of the
photoreceptors.
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50. 3.External limiting membrane (ELM).
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Not a true membrane
formed by attachment of
photoreceptors and Müller
cells
highly fenestrated.
Extents from the ora serrata to
the edge of optic disc.
Main function-
• Selective barrier for nutrients
• Stabilization of transducing
portion of the photoreceptors.
4. Outer nuclear layer
formed by nuclei of rods and
cones.
Rod nuclei form the bulk of
this layer.
51. 5.The outer plexiform layer (OPL)
Synaptic junction of photoreceptor and
the horizontal and bipolar cells.
In the fovea there is no synaptic because
cone pedicles are displaced laterally to the
extrafoveal region.
At the edge of the foveola, it lies almost
parallel to the internal limiting
membrane.
marks the junction of the end organs of
vision and first order neurons in retina
Function
Transmission and amplification of
electrical potential
The presence of numerous
junctions-Aids in the homeostasis
of the retina.
Act as a functional barrier to
diffusion of fluids and metabolites
dark maroon dot and blot hemorrhage
in deep retinal hemorrhage
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52. 6.The inner nuclear layer (INL)
Located betweeen OPL and
IPL
Consists of following 8-12
rows of cells: 4 nucli
Bipolar cells- 9 types
Horizontal- 3
types(H1,H11,H111)
Amacrine
Supportive Muller’s cells
for transduction and
amplification of light signal
The retinal blood vessels
ordinarily do not extend
beyond this point.
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53. 7.The inner plexiform layer (IPL)
Synapses bet. Axons of bipolar
cells and dendrites of ganglion
and amacrine cells.
The bipolar cell contracts two
processes, one from a
ganglion cell and the other from
an amacrine cell
8. The nerve fiber layer (NFL)
Formed by axons of the
ganglion cells.
Normally, these axons do not
become myelinated until
they pass through the lamina
cribrosa of the optic nerve
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54. Overall, cells and their processes in the retina
oriented perpendicular to the RPE in the middle
and outer
but parallel to the retinal surface in the inner layers.
For this reason, deposits of blood or exudates
form round blots in the outer layers (where small
capillaries are found)
linear or flame-shaped patterns in the nerve fiber
layer.
At the fovea, the outer layers also tend to be
parallel to the surface (Henle fiber layer).
radial or star-shaped patterns form
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55. Arrangement of nerve fiber in the Retina
Fibres from the nasal half superior and
inferior radiating fibres (srf andirf).
Fibres from the macular regiontemporal
part of the disck as papillomacular bundle
(pmb).
Fibres from the temporal retina arch
above and below the macular and
papillomacular bundle as superior and
inferior arcuate fibres (saf and iaf) with a
horizontal raphe in between.
The nerve fibre layer is thickest at the nasal edge
of the disc, where it measures 20-30 microns
decreased with increasing distance from the disc
margin
8 to 11 microns just posterior to the ora serrata
The papillomacular bundle represents
the thinnest portion of the nerve fibre
layer around the optic disc
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56. ARRANGEMENT OF NERVE FIBRES OF THE OPTIC
NERVE HEAD
Fibres form the peripheral
part of the retina lie
deep in the retina but
superficial part of the
optic disc.
fibres originating closer to
the optic nerve head lie
superficially in the
retina
central (deep) portion
of the disc.
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57. THICKENSS OF NERVE FIBRE LAYER AT THE DISC:
Thickness of the nerve fibre layer around
the different quadrants of the optic disc
margin progressively increasing order:
Most lateral quadrant (thinnest)
Upper temporal and lower temporal
quadrant
Most medial quadrant
Upper nasal and lower nasal quadrant
(thickest)
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58. Clinical significance
Papilloedema appears
first in the thickest quadrant (upper nasal and
lower nasal)
last of all in the thinnest quadrant (most lateral).
Arcuate nerve fibres which occupy the
superior temporal and inferior temporal
quadrants
most sensitive to glaucomatous damage
Macular fibres occupying the lateral quadrant
most resistant to glaucomatous damage
retention of the central vision till end
The loss of tissue seems to be associated with compaction
and fusion of the laminar plates
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59. 9. internal limiting membrane
innermost layer of the retina and the outer boundary of the vitreous
Both the retina and the vitreous contribute
Collagen fibrils
proteoglycans (mostly hyaluronic acid) of the vitreous;
the basement membrane;
the plasma membrane of the Muller cells and possibly other
glial cells of the retina
It continues uninterrupted at the fovea where it is thickest
At the periphery of the retina, the membrane is continuous with
the basal lamina of the ciliary epithelium
It gives the posterior retina a characteristic sheen when
observed with the ophthalmoscope
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60. Retina blood suplay
The outer retinal layers receive nutrition from the
choroidal capillary bed
The central retinal artery provides nutrients to the inner
retinal layers.
The artery enters the retina through the optic disc
slightly nasal of center, and branches into a superior and
inferior
nasal and temporal branches, and continue to bifurcate
The nasal branches run a relatively straight course toward
the ora serrata,
but the temporal vessels arch around the macular area en route to
the periphery.
located in the nerve fiber layer just below the transparent
internal limiting membrane
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62. A capillary-free zone 0.5 mm in diameter is free of all
retinal vessels.
Retinal blood vessels lack an internal elastic lamina & a
continuous layer of smooth muscle cells.
Retinal vessels are said to be “end vessels” because
they do not anastomose with any other system of
blood vessels.
Retinal vessels terminate in delicate capillary arcades
approximately 1 mm from the ora serrata.
The retinal capillaries are made up of a single layer of
unfenestrated endothelium
The endothelial cells are one part of the blood-retinal barrier
because they are joined by zonula occludens.
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63. Two capillary networks are formed.
The deep capillary network lies in the inner nuclear
layer near the outer plexiform layer
The superficial capillary network is in the nerve
fiber layer or ganglion cell layer.
The retina outer to the outer plexiform layer is
avascular
The outer plexiform layer is thought to receive its nutrients
from both retinal and choroidal vessels.
The middle limiting membrane usually is regarded as the
border between the choroidal and retinal supplies.
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64. A dense peripapillary network of capillaries, radially
arranged around the optic nerve head, follows the
arcuate course of the nerve fibers as they enter the
disc.
A cilioretinal artery is a vessel that enters the retina
from the edge of the disc
origin in the choroidal vasculature.
nourishes the macular area, is found in approximately 15%
to 20% of the population
A cilioretinal artery can maintain the viability of the macula
if blockage of the central retinal artery occurs.
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65. Fundus view of vessels
The retinal blood vessels are readily visible with the
ophthalmoscope, and because
the vessel walls are transparent,
the clinician actually is seeing the column of blood within the
vessel.
The lighter-colored blood is the oxygenated blood of the artery
the venous deoxygenated blood is slightly darker.
The artery generally lies superficial to the vein.
With aging and some disease processes, such as hypertension,
the arterial wall may thicken and constrict the vein; this is called
arteriovenous nicking.
In some individuals the pigmented choroid and it svessels are
visible through the retina, and the choroidal
vessels appear as flattened ribbons
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Neuroglial cells, although not actively involved in the transfer of neural signals, provide structure and support and play a role in the neural tissue reaction to injury or infection. Types of neuroglial cells found in the retina include Müller cells, microglial cells, and astrocytes.
