Download VS 206D-Fall10 Retina

R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
I. A NATOMY OF THE R ETINA
Introduction
The retina is the light-sensitive layer of the eye that, via the
phototransduction that takes place in its rods and cones, first detects the image
focused upon it by the eye’s optics, and then signals the brain about aspects of
the real-world objects represented in that image. Together with the optic nerve,
the retina comprises the “nervous tunic”-- the innermost of the eye’s three major
tunics (connective = outer, vascular = middle). The English word “retina” comes
from the Latin “rete,” which refers to a net or network. The retina is commonly
considered to be central nervous system tissue displaced into the eye.
1. Functional Aspects of the Retina
Nutritive: The retina has an extremely high metabolic rate, especially its
photoreceptors. As a result, it enjoys an unusually abundant, dual supply of blood to 1)
provide it with oxygen, 2) carry away its metabolites and 3) keep it from over-heating.
Structural: The retina is a dense, compact, but very fragile tissue that is
tenuously attached internally to the vitreous body and externally to the retinal pigment
epithelium (RPE). The IOP normally acts to hold the retinal sheet smooth and in
apposition to the RPE. The retina is thickest (560 µm) around the optic disc (i.e., in the
peripapillary region), and thinnest peripherally (100 µm), where it merges with the
ciliary body (pars plana) in the ora serrata region. Much of the structural integrity of the
retinal tissue is owed to the presence of the Müller cells, a network of large glia whose
cell bodies span its full thickness and branch extensively within its various layers.
Neurophysiological: The retina not only transduces fluctuations in incident light
energy to changes in neural membrane potential, it processes these neural signals and,
via the long axons of its ganglion cells, conveys action potentials to neurons in
numerous visual areas in the brain.
Page 1 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
2. Layers of the Retina
Overview: Classically, the retina has been described as consisting of 10
“layers,” some of which contain the cell bodies of epithelia, neurons or glia, and others
the processes (e.g., dendrites, axons) of neurons and their interconnections (i.e.,
synapses), and glia. Two were historically described as “membranes,” but are now
understood to consist of the junctions between neurons and glia or glial expansions:
(most external )
1. Retinal Pigment Epithelium (RPE)
2. Rods and Cones (Photoreceptor Layer)
3. Outer (External) Limiting Membrane (OLM/ELM)
4. Outer (External) Nuclear Layer (ONL/ENL)
5. Outer (External) Plexiform Layer (OPL/EPL)
6. The Inner (Internal) Nuclear Layer (INL)
7. Inner (Internal) Plexiform Layer (IPL)
8. Ganglion Cell Layer (GCL)
9. Nerve Fiber Layer (NFL)
10. Inner (Internal) Limiting Membrane (ILM)
(most internal )
Page 2 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Cell types in the mammalian retina
Page 3 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
1. Retinal Pigment Epithelium (RPE): The outermost (or most external) retinal
layer consists of a single sheet of heavily pigmented, hexagonally-shaped epithelia – 46 million of them per eye. The RPE cells are smaller (~14 µm across), but more heavily
pigmented, near the center of the retina than they are in the peripheral retina, near the
ora serrata (~60 µm across). RPE cells undergo little postnatal mitosis; instead they
stretch to accommodate growth of the globe and do not regenerate if they are lost. The
RPE is critical to the normal functioning of the rod and cone photoreceptors, whose
outer segments its cells partially engulf. The RPE’s functions include 1) maintaining the
adhesion of the remainder of the retina, 2) providing a selectively permeable barrier
between the choroid and the retina, 3) phagocytosis of the rod and cone outer
segments, 4) synthesis of the inter-photoreceptor matrix, 5) absorption of stray
light/reduction of scatter within the eye, and 5) transport and storage of metabolites and
vitamins. Externally, Bruch’s membrane separates the RPE from the choriocapillary
layer of the choroid.
Page 4 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Page 5 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
2. Rods and Cones (Photoreceptor Layer): The rod and cone cells are
modified cilia containing specialized photo-labile pigments that are the key ingredient in
the phototransduction process. Each eye contains 90-100 million rods and 4-5 million
cones nonlinearly arrayed across the retina (see below). Each photoreceptor cell
consists of 1) an outer segment that is partially engulfed by the RPE and contains a
stack of discs impregnated with photopigment molecules, 2) an inner segment that is
filled with mitochondria and is continuous with the cell’s nucleus and its axon, and 3) a
narrow connecting cilium that joins the two segments.
Page 6 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
3. Outer (External) Limiting Membrane (OLM/ELM): The OLM lies in a 1µmthick plane at the internal end of the photoreceptor cells’ inner segments, separating
them from their nuclei and synapses. Historically thought to be a fenestrated
membrane through which the photoreceptors poked, the OLM is now known to consist
of a two-dimensional array of adhering junctions (maculae adherens) between 1)
photoreceptor inner segments and processes of Müller cells (glia), 2) adjacent
processes of Müller cells, and 3) occasionally between neighboring inner segments.
The OLM’s function is not certain, although it is clearly structural. It’s barrier-like feature
also affects the way ionic currents flow around the photoreceptors.
Page 7 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
4. Outer (External) Nuclear Layer (ONL/ENL): The ONL contains the soma of
the rod and cone photoreceptor cells with their nuclei.
5. Outer (External) Plexiform Layer (OPL/EPL): The OPL consists of the
synaptic endings of the rod and cone photoreceptor cells onto the processes of the
horizontal and bipolar cells, along with processes of the Müller cells (glia).
6. The Inner (Internal) Nuclear Layer (INL): Contains the soma (and nuclei) of
the horizontal, bipolar and amacrine neural cells, as well as those of the Müller cells.
7. Inner (Internal) Plexiform Layer (IPL): The IPL consists of the processes
and synapses of the bipolar, amacrine and ganglion cells, as well as processes of the
Müller cells.
Page 8 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
8. Ganglion Cell Layer (GCL): This layer contains the nucleated cell bodies of
the around 1.1 million ganglion cells that are found in each retina.
9. Nerve Fiber Layer (NFL): This layer is composed of the axons of the
ganglion cells, which converge in a distinctive pattern from all parts of the retina to the
optic disc (see below), where they leave the eye and form the optic nerve (CN II).
These unmyelinated axons are surrounded by processes from astrocytic and Müller glial
cells.
10. Inner (Internal) Limiting Membrane (ILM): The 1-to-2µm-thick ILM covers
the internal surface of the entire retina (but not the optic disc), and is formed by the
expanded “foot-like” processes of the Müller glial cells. Again, like the OLM, the ILM is
not a true membrane but rather a barrier between the retina and the vitreous chamber.
The collagen fibers of the vitreous body are adherent to the ILM, which can lead to
traction on the internal surface of the retina and even retinal detachments as the
collagenous portion of the vitreous shrinks with age.
Page 9 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
3. Regional Anatomy of the Retina
Overview: The cells in the ten layers of the retina are not uniformly arrayed
across the retinal sheet. Instead, the retina is characterized by distinct regional
specializations, where not all the layers are present and the density of the different cell
types varies dramatically. These areas of retinal specialization have a profound impact
on the way our visual system perceives the outside world.
Central Retina: Various terms are used to describe the 5-6mm-diameter region
at the center of the retina that represents the central 180 of our visual field. Anatomists
use specific changes in the histological features of the 10 layers of the retina to define
the boundary of this central region and to distinguish several sub-regions within it.
Clinicians use appearance of the funduscopic image, the architecture of the retinal
blood vessels and linear dimensions (expressed in optic-disc-diameter units) to refer to
some of these same regions.
Macula/Macular Region/Central Retina/Posterior Pole: These terms
are used (often rather loosely) to refer to the 5-6mm wide region of the retina at the
posterior pole of the eye. Histologically, its peripheral limit is precisely defined as the
point where the multi-layered ganglion cell layer is reduced to just a single layer of cells.
The peripheral limit of this region is much harder to define based on gross anatomical
changes or characteristics of the ophthalmoscopic image. Hence, clinicians typically
refer to it as the approximately 4-disc-diammeter region whose center lies slightly below
and 2.5-disc diameters temporal to the optic disc. Note that the nasal boundary of the
macula is roughly tangent to the temporal rim of the optic disc.
MACULA. This figure shows the
relationship between the central
retinal regions with the macula to
their histological features. The
boundaries of the regions as they
appear in a fundus photograph are
aligned with their equivalent
histological landmarks in a
meridional section of the retina.
The fundus photograph indicates
the locations of the foveola (a),
fovea (b), parafovea (c) and
perifovea (d). The approximate
dimensions of these various
regions are indicated in the space
between the two images.
Page 10 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Sketch, redrawn from the previous figure to show the location of the macula lutea and to
indicate the number of rows of ganglion cells present within each region of the macula.
Page 11 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Fovea (Central Fovea, Fovea Centralis): At the center of the macula
lies the fovea, an approximately 1.5mm-diameter region whose center is located about
4mm temporal and 0.8mm below the center of the optic disc. The retina thins to a
thickness of only about 130µm in the central fovea as its inner layers are progressively
displaced centrifugally, toward the outer edge of the fovea. Thus, the central fovea
contains only the RPE, photoreceptor, OLM, ONL, OPL and ILM layers. The fact that
the bipolar cells to which the central foveal photoreceptors have to connect have been
displaced to the sides means that the elongated axonal processes of the photoreceptors
have to run obliquely to make their synapses. These radially oriented, elongated
processes are stacked upon on each other, creating a new retinal layer in the fovea
known as Henle’s fiber layer. There are only cone photoreceptors in the central
300µm (1o of visual angle) of the fovea, a subregion known as the foveola. These
central foveal cones are highly elongated and narrow, so that they appear almost rodlike. They are also very densely packed -- their density reaches 200,000 cones/mm2.
Thus, the foveola, which represents the central 1o of our visual field (your little finger,
held at arm’s length, subtends about 1o), contains a total of only around 4,500 cones.
The internal surface of the fovea is concave, and when viewed ophthalmoscopically its
smooth ILM reflects and condenses light, creating the “foveal reflex.”
This figure shows the displacement of the retinal layers, with the subsequent formation
of Henle’s fiber layer, that occurs in the fovea.
Page 12 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Parafovea: The 0.5mm-diameter annulus of retina immediately
surrounding the fovea is known at the parafoveal. Henle’s fiber layer is very thick here
and this region contains the highest density of neurons in the retina, owing to the
displacement of cells out of the central fovea.
Perifovea: The outermost annular ring of the macula, measuring 1.5mm
in width, is known as the perifovea.
Macula lutea: Within the macula, there is a zone centered on the fovea
that measures about 2mm horizontally and 0.9mm vertically and is characterized by the
presence of a special pigment (xanthophyll), which turns a bright lemon-yellow color in
freshly excised retinas. This pigment, which is distributed throughout the retinal layers,
is especially dense in the OPL, and is thought to provide protection to the retinal cells by
filtering out potential harmful UV light. The macula lutea also gives rises to the clinically
useful entoptic phenomena known as “Maxwell’s spot” and “Haidenger’s brushes.”
Page 13 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Peripheral Retina: At its periphery, the retinal layers thin and ultimately merge
with the layers of the ciliary body.
Ora serrata: This term, which translates from the Latin to “serrated ring,”
refers to the serrated (“teeth and bays”) appearance of the retinal termination at its
border with pars plana of the ciliary body. The retina thins peripherally as its layers
gradually disappear, proceeding generally from internal to external. The collagen fibers
of the vitreous body are particularly well attached to the ILM near the ora serrata and
this, together with its thinness and the normal degenerative changes it undergoes with
aging (e.g., cystoid retinal degeneration), makes the retina susceptible to detachments
in this region.
Page 14 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Photograph of ora serrata region in an elderly patient. a) small or accessory ciliary
processes of pars plicata of the ciliary body. b) typical dentate processes (or “teeth”) of
the ora serrata, with “scalloped bays” in between. c) enlarged dentate process that
forms a meridional fold (d) in pars plana of the ciliary body that merges with one of the
major ciliary process of pars plicata (unlabeled white structures at top). e) cystoid
retinal degeneration typical for eyes of this age. arrow) hole in the peripheral retina.
Page 15 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Variations in the Density of Retinal Cells: The horizontal distribution of cells
across the retinal expanse is highly non-uniform. Cone photoreceptors are at their
highest density (about 200,000/mm2) in the foveola, where there are no rods. The rods
reach their peak density (about 150,000/mm2) about 20o from the foveal center, near the
outer edge of the macula. There are few-to-no ganglion cells in the foveola, and their
density rises to its peak (about 35,000/mm2) around 1.5mm from its center, in the
parafoveal region.
Rod and cone density as a function of eccentricity along the retinal horizontal meridian.
Photographs are optical sections through inner segments, showing rods and cones at
different distances from foveal center. Distances (above each photograph) are in mm,
and locations of various images are mapped onto rod and cone density curves below.
Except for central image (0.0), which contains only cones, larger cells in each image are
cones and smaller rods. Gap in nasal side of density curves marks location of optic
nerve head.
Page 16 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
4. Blood Supply of the Retina
Overview: The retina is extremely metabolically active, with the highest oxygen
consumption (per weight) of any human tissue. Like the rest of the brain, the retina has
a highly selective blood-tissue barrier that maintains a regulated homeostatic
environment in this sheet of specialized neural tissue. The retina has a dual blood
supply, with its inner layers (ILM, NFL, GCL, IPL, INL and OPL) being fed by branches
of the central retinal artery, and its outer layers (ONL, , OLM, Photoreceptor and RPE)
receiving blood from the choroid. Hence, reviewing the blood supply of the retina
requires an understanding of the ocular blood supply.
Central Retinal Artery and Vein: Typically the first branch of ophthalmic artery
(itself the seventh branch of the internal carotid artery), the central retinal artery arises
from the ophthalmic in the posterior orbit and runs beneath the optic nerve to a point 1213mm behind the globe, where it pierces the nerve, passes to the its center and
emerges inside the eye at the center of the optic disc. In the eye, the central retinal
artery bifurcates into superior and inferior branches, which run on the internal surface of
the retina, in turn bifurcating into nasal and temporal branches. This bifurcating
Page 17 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
branching pattern continues as the artery distributes blood across the retina in eversmaller branches. The central retinal vein and its branches accompany those of the
artery. The central retinal vessels support four intra-retinal capillary beds (i.e., layers)
that lie on both sides of the GCL and on both sides of the INL. An exception to this
pattern occurs in the fovea, the central 500µm of which is capillary-free.
The pathway taken into and out of the eye by the
central retinal artery and vein, respectively.
Funduscopic image showing optic nerve head, retinal arteries (lighter)
and veins (darker) with their characteristic bifurcating branching pattern,
and macular pigment. Note how vessels radiate across the retina nasal
to the optic disc, but arch around the foveal region temporally.
Page 18 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Page 19 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Choroid: Together with the iris and the ciliary body, the choroid forms the
middle or vascular tunic of the eye, which is also known as the uveal tract. The choroid
is to the retina as the pia and arachnoid maters are to the rest of the brain. The
choroid’s principal function is to nourish the outer layers of the retina (ONL, , OLM,
Photoreceptor and RPE), but it also helps to thermoregulate the photoreceptors and it
absorbs stray light via its heavily pigmented outer region, which is known as the
suprachorid. Internally, the choroid contributes to the formation of Bruch’s membrane,
which lies between the choroid and the RPE.
Blood is supplied to the choroid via branches of or derived from the ophthalmic
artery, including the two long posterior ciliary arteries, numerous short posterior ciliary
arteries and the seven anterior ciliary arteries. Blood is drained from the choroid via the
four vortex veins, seven anterior ciliary veins and numerous pial veins. Progressing
from external-to-internal through the choroid, the caliber of the blood vessels goes from
large (in the external or Sattler’s region of the choroid) to medium (in the middle or
Haller’s region) to capillaries (in the internal choriocapillary layer or choriocapillaris).
The rate of transition from large vessel to capillary occurs more rapidly here than
anywhere else in the body.
The flattened capillaries of the choroid are extra-wide (capable of passing 2-3
RBC’s abreast) and fenestrated on their internal surfaces, and they are thought to be
even more permeable than those elsewhere in the brain. Blood flows through them at a
rate around seven times higher than that in the retinal capillaries.
A) Diagram of choroidal
blood supply. (LPCA –
long posterior ciliary
artery; SPCA – short
posterior ciliary artery)
B) Choroidal histology.
(CC – choriocapillaris; HL
– Haller’s Layer; SL –
Sattler’s Layer)
C) Plastic cast of choroid,
viewed from external side.
(VV – vortex vein)
D) Diagram of “hexagonal
units” in choriocapillaris
fed by small arterioles.
E) Plastic cast of
choriocapillaris, viewed
from internal side.
Page 20 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Page 21 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Page 22 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Page 23 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Diagram illustrating the dual but essentially non-overlapping nature of the retinal
blood supply. At the top, the choroid (via the choriocapillaris) nourishes the external
retinal layers, including the RPE, OLM and photoreceptors (inner and outer segments).
At the bottom, the central retinal artery and vein nourish the inner retinal layers,
including the OPL, INL, IPL, GCL, NFL and ILM.
Page 24 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
5. Clinical Considerations of the Retina
Retinal Imaging Techniques
Funduscopy: The use of visible light to view the fundus of the eye
(“funduscopy”) traces its origin to Helmholtz, who in 1851 realized that by peering at the
eye through a peephole in a mirror held at 45o to the visual axis and shining light into
the eye, he could see the light reflected from the retina. Ophthalmoscopy, as it came to
be called, moved forward with the invention of the hand-held, direct illumination
ophthalmoscope by Welch and Allyn in 1915. The principle of shining visible light onto
the retina and viewing the reflected image is behind many modern viewing systems,
including the binocular indirect ophthalmoscope (BIO) and fundus camera (see fundus
image on page 18). Many aspects of the diagnosis and treatment of ocular (and even
systemic) diseases still rely upon this 150-year-old technique for viewing the anatomical
features of the fundus.
Fluorescein Angiography: Although many of the larger blood vessels
responsible for nourishing the retina can be viewed ophthalmoscopically, others are
hidden by the retinal layers and/or too small to resolve. In addition, funduscopy
provides limited information about the movement of blood through the intraocular
vascular system. Fluorescein angiography utilizes the intravenous injection of a
harmless fluorescent dye (sodium fluorescein) and video funduscopy performed with
ultraviolet light to reveal the progression of fluorescein-labeled blood through the retinal
vessels (arteries  capillaries  veins). Since the large dye molecule normally does
not leak out of the retinal or choroidal capillaries, any dye left behind in the eye reveals
places where seepage has occurred, and dye-free regions indicate areas where the
circulation has been compromised.
Diagram of the procedure for performing fluorescein angiography.
Page 25 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Normal fluorescein angiographic images (from three different eyes). On the left, the
arteries have filled and the veins are just beginning to fill. Note the slight lamination of
the die in the veins. In the middle image, venous filling has progressed and lamination
is more pronounced. The image on the right is from a slightly later stage in the
procedure. The venous lamination is much less pronounced and the overall density of
the die in the arteries and veins is similar.
Optical Coherence Tomography (OCT): Tomography (from the Greek
word tomos, which means "a section," "a slice" or "a cutting") refers to imaging of tissue
produced by combining sections or slices. In OCT, changes in the coherence of light
reflected from the fundus compared to that in a reference beam reflected from a mirror
are used to generate noninvasive, in-vivo, 3-D images of the fundus tissues to a depth
of 2-3mm. Current OCT methods can resolve structural details in the sub-micron range,
delivering high-resolution images and
quantitative analysis of tissues,
including the retina. These images
and the data provided by their
analysis have greatly improved both
the diagnosis and the treatment of
retinal disease.
OCT Instrument (Zeiss)
Page 26 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
High-resolution images of the internal retinal structure can be taken with optical coherence
tomography (OCT), and this figure demonstrates the processes involved in using this technology.
(A) Low-coherence infrared light is transmitted into the eye through use of an interferometer. (B)
The infrared light is transmitted through the pupil and then penetrates through the transparent
layers of the retina. Subsequently, the light backscatters and returns through the pupil, where
detectors can analyze the interference of light returning from the layers of the retina compared
with light traveling a reference path of identical length (mirror #2). An algorithm mathematically
uses this information to construct a gray-scale or false-color image representing the anatomy of
the retina (shown in the upper right portion of the figure). (C) A fundus image from the OCT
device, showing the optic disc appropriately centered and surrounded by the target image
circumference marker for analysis of the retinal nerve fiber layer.
Page 27 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
OCT image of normal retina. Cross-sectional image taken through the fovea.
Top – Funduscopic image of normal retina. Bottom – Spectral OCT image from scan taken
through the macula, showing foveal region, retinal layers and choroidal vessels.
Page 28 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Top -- OCT image through foveal region of normal retina with computerized
determination of the boundaries between major retinal layers. Bottom – Portion of top
image, enlarged to show change in retinal layering in the foveal rim.
Page 29 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Spectral OCT. 3D optical-coherence tomography (OCT) at 800 and 1060nm of (a)–(d) a
normal retina and (e)–(h) a patient with retinitis pigmentosa. (b, f) High-definition (4096 depth
scans) 800nm 3D OCT scan over 35°. (d, h) High-definition (2048-pixel) 1060nm 3D OCT scan
over 35°. (c, g) En-face wide-field (35°×35°). (a, e) En-face zoomed-in fundus image of the
choroid using 1060nm 3D OCT. Arrows indicate enhanced choroidal visualization.
Page 30 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
3D visualization of volumetric retinal OCT data. Image A shows the whole retinal volume.
Image B shows the left part of the volume removed by XZ clipping plane. Image C shows the
left part of the volume removed by YZ clipping plane. Image D shows a segmented region of
the volume.
Page 31 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Top – Spectral OCT image of scan through the fovea of normal retina, rendered in false
color. Bottom -- High-magnification, 3D-reconstruction (from individual 2D scans like
the one above) of the central retina, showing the foveal “pit.”
Page 32 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Retinal Detachments: Embryologically, the inner, “neural” layers of the retina
and its outer “epithelial” layer (RPE) are derived from the inner and outer layers of the
invaginated optic cup, respectively. During development, the primitive space that lies
between these two layers ultimately disappears. However, the legacy of this intraretinal
space remains -- the interface between the neural retinal and the RPE is tenuous even
into adulthood. Although normally only a potential space, the subretinal space can
reappear as a result of the accumulation of fluid between the retina and the RPE. When
this occurs, the retina “detaches” from the RPE. The contributing factors to retinal
detachment are many. They include trauma to the eye, physical traction on the inner
surface of the retina (pulling it away from the RPE) as well as edema caused by the
seepage of fluid (e.g., blood, exudates) into the intraretinal space.
Page 33 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Page 34 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Retinal Hemorrhages and Exudates: Aspects of retinal anatomy determine the
ophthalmoscopic appearance of a retinal hemorrhage or exudate (fluid that has filtered
from a blood vessel into the retina). Thus the appearance of a hemorrhage or an
exudate is a clue as to its retinal location. Since the NFL is oriented parallel to the ILM,
hemorrhages in this layer appear to be “flame-shaped” ophthalmoscopically. Since the
“grain” of the deeper retinal layers is oriented perpendicular to the ILM, hemorrhages in
these layers (e.g., (IPL, INL, OPL, ONL) are seen “end-on” and appear to be “dots.”
Exudates typically accumulate and diffuse in the OPL, especially in the macula, and
they have a more amorphous appearance (e.g., clumped, cloud-like).
Page 35 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Retinal Signs of Systemic Hypertension: Chronically elevated systemic blood
pressure may cause the walls of the retinal arterioles to thicken, resulting in a narrowing
of their lumina. These sclerotic arterioles may compress the softer veins wherever they
cross over them. Exudates, produced by damaged retinal vessels, may accumulate in
the OPL
Page 36 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Drusen: Material sometimes accumulates within Bruch’s membrane, pushing
the photoreceptors inward, away from the choriocapillaris. The nature of this material
(e.g., proteins, lipids) and its appearance (e.g., yellow, white) varies according to the
condition causing it to form. The local aggregations can have borders that are sharply
delineated (“hard or calcified”) or more diffuse (“soft”), but in each case they are called
drusen. Drusen that are numerous and spread over a region of the retinal are said to
be “confluent.” If a druse becomes large, the overlying photoreceptors can degenerate,
causing a loss of vision.
Fundus image showing soft and hard drusen.
Histological image of a druse (a) in Bruch’s membrane from older eye. (b) shows age-related
accumulation of dense material in Bruch’s membrane. Note RPE disruption above the druse.
Page 37 of 38
R.C. V AN S LUYTERS
VS 206D
F ALL 2010
N EUROANATOMY / PHYSIOLOGY OF THE E YE & V ISUAL S YSTEM
Fundus photograph of soft, confluent drusen in an older eye.
Page 38 of 38