Introduction to Basic Anatomy and
Physiology of Vision
Alan D. Letson, MD
Professor & William H. Havener Chair in Ophthalmology
Department of Ophthalmology
Alan.Letson@osumc.edu
Primary Objective
 Describe the organization of the retina and mechanisms
involved in photo transduction.
Objectives
 Describe the arterial blood supply to the orbit, retina
and anterior optic nerve
 Describe the blood supply to the visual cortex
 Describe venous drainage of the eye and orbit.
 Describe retinal anatomy and histology
 Describe the visual cycle of 11 –cis-retinal to all-trans
retinal and the relationship of the photoreceptor to the
retinal pigment epithelium in this cycle
 Describe the relationship of the visual cycle to photo
transduction.
 Describe photo transduction and the resultant change
in photoreceptor cell polarization and effects at the
photoreceptor –bipolar cell synapse
 Describe the relationship of retinal anatomy to
production and organization of visual stimuli
Note
 This module contains a number of “demonstration
slides”. These are included to enhance your appreciation
of the complexity of the retinal neural organization but
are not required for testing purposes. These will be
indicated in the notes and narration as “elective” slides.
Additional Resources utilized for this
module
 Ryan (editor): Retina, vol 1, 5th edition, 2013 Pages 330430
 Basic and Clinical Science Course*:
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Volume 2 Fundamentals and Principles of Ophthalmology
Volume 5 Neuro-Ophthalmology
Volume 12 Retina and Vitreous
* American Academy of Ophthalmology
What does the retina do?
Blood supply to the visual system
A
Internal and
external
carotid artery
collateral
systems
Rod outer segments
furrows
cleft
Insert fig 8-2 spencer
IRBP
Figure 4-6 Photoreceptor mosaic
in the primate retina. At the fovea,
the cones are small and tightly
packed. With increasing
eccentricity, rods appear between
the cones until, in the periphery,
they are numerically dominant. In
this photo the cones are larger
than rods. The distance is
measured from the foveal center
(From Wikler KC, Williams RW,
Rakic P. Photoreceptor mosaic:
number and distribution of rods
and cones in the rhesus monkey
retina. J Comp Neurol
1990:297:499-508.
Figure 4-6 Photoreceptor mosaic in the
primate retina. Farther from the fovea, the
numbers of rods increase while cone
numbers decrease. Distance is measured
from fovea. From Wikler KC, Williams RW,
Rakic P. Photoreceptor mosaic: number
and distribution of rods and cones in the
rhesus monkey retina. J Comp Neurol
1990:297:499-508.
Figure 4-10 The mosaic of red, green and
blue cones in the human retina. This
image, taken from a human subject using
adaptive optics, shows the distribution of
the three cone classes. Blue cones make
up a small fraction, 10%, but make a
regular mosaic. Red and green cones
have a clumpy, random distribution. In
this subject, the red cones outnumber the
green cones but this ratio is highly
variable, even in subjects who have
normal color vision. Image courtesy of
Austin Roorda, after Roorda A, Williams
DR. The arrangement of the three cone
classes in the living human eye. Nature
1999;397:520-522..
Vertical retina:
Glutamate - excites
Horizontal
retina:
inhibitory
Parallel pathways. A highly
filtered image, 13 x 20
pixels containing mostly low
spatial frequency
information. At first, it may
be hard to recognize
because it is natural to
focus on the pixel edges.
However, if you squint to
blur the image, the true
identity of the picture may
suddenly be more obvious.
This is a direct
demonstration that the
visual system carries
several (approx. 15) parallel
streams of visual
information with different
spatial properties mediated
through different ganglion
cell types.
Figure 4-19 ON and OFF pathways.
The opposite responses of ON and
OFF cone bipolar cells are generated
by the expression of different
glutamate receptors. OFF bipolar
cells are depolarized by glutamate,
the photoreceptor transmitter, hence
the + for a sign conserving synapse.
ON bipolar cells are hyperpolarized
by glutamate, hence the - for a sign
inverting synapse. This unusual
receptor is called the mGluR6
receptor. It is selectively activated by
the glutamate analog APB and it is
responsible for the separation of ON
and OFF signals through the visual
system. Furthermore, the inner retina
is functionally stratified. OFF bipolar
cells ramify in sublamina a and ON
bipolar cells descend to sublamina b.
Both bipolar cell types use glutamate
and they make excitatory synapses
with amacrine and ganglion cells.
Glutamate receptors map the
rod/cone mosaic. mGluR6
receptors (red) mark the tips of rod
bipolar cells where they enter the
rod spherule. A small cluster of ON
cone bipolar dendrites are also
lightly marked at each cone pedicle.
GluR5 receptors (blue) mark OFF
bipolar cell basal contacts at each
cone pedicle. Thus, this
combination of glutamate receptor
antibodies conveniently marks the
positions of rod and cone terminals.
Courtesy of Pan and Massey SC.
OFF bipolar cells contact
cones. An OFF bipolar cell
was filled with Lucifer
yellow (green). In
wholemount, with the
focus at the OPL, fine
dendrites extend to
contact every cone within
the dendritic field. The
positions of rod and cone
terminals are marked with
a combination of
glutamate receptor
antibodies mGluR6 (red)
and GluR5 (blue).
Figure 4-15 B-type horizontal cells in the rabbit retina. A, A single B-type horizontal
cell filled with Lucifer yellow contacts all the cone pedicles (white outlines) within its
dendritic field. Arrow shows the axon leaving the frame. A, courtesy of Li W and
Massey SC; A series of biotinylated tracers distinguishes three types of gap junction
in retina. J Neurosci 2000;20: 8629-8636. With permission from the authors and the
society for Neuroscience.
B, The rod/cone mosaic is shown by labeling postsynaptic glutamate receptors,
GluR5 (blue) and mGluR6 (red). The A-type horizontal cells contact every cone in the
frame.
Figure 4-14 A-type horizontal
cells in the rabbit retina. A,
The coupled matrix of A-type
horizontal cells following the
intracellular injection of
Neurobiotin (green) in the
rabbit retina. B, The rod/cone
mosaic is shown by labeling
postsynaptic glutamate
receptors, GluR5 (blue) and
mGluR6 (red). The A-type
horizontal cells contact every
cone in the frame. C, At high
resolution, fine horizontal cell
dendrites (green) converge at
individual cone pedicles. D, In
the triple label image, the
horizontal cells terminate at
cone pedicles. The green, red
and blue labels are not colocalized. They label
independent neuronal
structures: horizontal cells,
ON bipolar cells and OFF
bipolar cells, respectively.
Courtesy of Pan and Massey
SC.
Figure 4-33 Amacrine cell morphology. This figure shows the
comparative morphology of 24 distinct amacrine cell types from the
rabbit retina. Courtesy of Masland D. Neuronal diversity in the
retina. Curr Opin Neurobiol 2001; 11:431-436. With permission from
the author and Elsevier.
Figure 4-36 S1/S2 matrix. A,
The S1/S2 matrix (green),
stained by serotonin uptake,
from wholemount rabbit retina.
B, Rod bipolar terminals (blue)
fill holes in the S1/S2 matrix.
Figure 4-36 S1/S2 matrix. A,
The S1/S2 matrix (green),
stained by serotonin uptake,
from wholemount rabbit retina.
B, Rod bipolar terminals (blue)
fill holes in the S1/S2 matrix. C,
AII dendrites (red) also contact
the same rod bipolar terminals.
D, Merged triple label image
shows S1/S2 processes and AII
dendrites surrounding every rod
bipolar terminal. From Zhang J,
Li W, Trexler EB and Massey
SC. Confocal analysis of
reciprocal feedback at rod
bipolar terminals in the rabbit
retina. J Neurosci 2002;
22:10871-10882. With
permission of the authors and
the Society for Neuroscience.
Figure 9-34 The midget system of the primate retina. The red and green cones each
activate two bipolars (ON and OFF) that subserve ON and OFF ganglion cells. The
blue system is different: blue cones connect with ON-bipolars, but not OFF-bipolars,
and the blue cone bipolars are represented by a special class of bistratified bipolar
cell. These cells feed into the parvocellular layer of the lateral geniculate. (From
Schiller PH. Prog Retin Eye Res 1995; 15:173-196.)
Figure 9-35 The parasol, or M ganglion, cell system is one in which a single, large field ganglion cell
receives input from all three cone types, producing a cell that is less interested in color and more
interested in luminosity or brightness discrimination. These cells feed into the magnocellular layer of
the lateral geniculate. (From Schiller PH. Prog Retin Eye Res 1995; 15:173-196.)
Summary items to know:
 The blood supply of the inner retina and superficial
optic disc is derived from the central retinal artery.
 The outer retina (photoreceptor layers), optic disc
and choroid receive blood from the short posterior
ciliary arteries,
 All these are branches of the ophthalmic artery – the
first intracranial branch of the internal carotid
Summary items to know
 Our external world is organized point by point, spatially,
through sequential synapses from the retina through the
visual cortex, each particular portion having a different
blood supply.
Summary items to know
 The vitamin A visual cycle between the retinal
pigment epithelium and the photoreceptor recycles
and provides the material sources (Rhodopsin,11-cis
retinal and all-trans retinal) that are required to
initiate photo transduction. The specific biochemical
steps do not need memorizing, but the general
process should be understood.
Summary items to know
 Photo transduction converts light energy into a neural
impulse. While the specific biochemical steps do not
need memorized, a general description of what
happens when light is absorbed by Rhodopsin, the
changes that occur when the cation gate is closed
and the subsequent hyper polarization of the cell with
its subsequent effect on glutamate release at the
synapse should be understood.
Summary items to know
 The electrical and subsequent neurotransmitter changes
that are initiated by photo transduction are transmitted
“vertically” through the retina by photoreceptors, bipolar
cells and retinal ganglion cells. The axons of the retinal
ganglion cells synapse in the LGN or pretectal nuclei.
Summary items to know:
 This vertical transmission of neural impulse is heavily
modulated by “horizontally” inhibitory actions by horizontal
cells and amacrine cells, and the receptive fields with onoff zones. This modulation results in the final output from
the ganglion cells. This output is in the form of graded
responses of various types of simultaneously streaming
visual channels of information that provide the
components of our vision ( color, contrast, contour, etc).
Thank you for completing this module
Questions? Contact me at:
Alan.Letson@osumc.edu
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