anatomy of retina

1. Dr.Lhacha Wangdi
Resident
Ophthalmology, JDWNRH
RETINA AND LAYERS

2. OBJECTIVES
1. Macroscopic anatomy of Retina
2. Retinal layer anatomy
3. Clinical correlates

3. GROSS ANATOMY-REVIEW
The retina proper is a thin and delicate layer of nervous tissue- covers ¾ of inner eye wall
Grossly retina is divided into two parts;
Central retina
1. Foveala
2. Fovea
3. Para fovea
4. Peri
5. Macula
Rich in cones, has more ganglion cells per
area than elsewhere, and is a relatively
small portion of the entire retina.
Clinical function
• Designed for fine visual acuity,
• Photopic vision
• Stereopsis‘,
• Color vision
Peripheral retina
1. Near periphery
2. Mid periphery
3. Far periphery
4. Ora serrata
Makes up most of the retina, and rods
dominate
Clinical function;
• Designed for gross vision and
• Scotopic/night vision
• Sensitive to motion and stimulates
turning of eye/head

4. CENTRAL RETINA/POSTERIOR POLE- OVERVIEW
Macula-
-Demarcated by superior
and inferior temporal
arterial arcuate
-Elliptical shape
horizontally
-Average diameter of
about 5.5 mm/3.5DD
-Area centralis
corresponds to
approximately 15-18° of
visual field
Fovea
-center of macula
-It has a diameter of 1.5-1.85mm/1DD
-Represents 5° of the visual field)
Foveola/fovea centralis
-Centre of fovea ( highest visual acuity)
-4 mm temporal to the centre of the optic
disc
and about 0.8 mm below the horizontal
meridian
-0.35mm in D/0.3-0.4DD
-corresponds to FAZ and 1°
of visual field
-Umbo (Center of foveola)
corresponds to light reflex
0.8mm
4 mm
Parafovea
-0.5mm around the
fovea
Perifovea
-1.5mm around the
parafovea

5. MACULA
Macula-Dark area in the central retina
Protects central vision by following characteristics;
1. Highly pigmented tall epithelial cells of
RPE(highest pigmentation of entire retina)-
which give dark macula
2. Dense pigmentation helps to reduce scattering
of light
3. The choroidal capillary bed also is thickest in
the macula
4. It has also yellowish hue due to highest
concentration of xanthophyll pigments
Function of xanthophyll pigments;
• Act as filters, absorbs short wavelength visible light to reduce chromatic aberration
• Antioxidant effect,
• Protective role against UVR damage.

6. 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
A disc diameter central depression in macula- fovea
• Central depression foveola is formed by lateral
displacement of retinal neurons leaving only
photoreceptors in the center.
• 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
FOVEA
(Fovea)
Foveola

7. CTN…
• Six layers present in the foveola are ;
(1) internal limiting membrane
(2)Henle’s fiber layers
(3) ONL (which contains about 10 rows of cone nuclei),
(4) external limiting membrane,
(5) photoreceptor layers
(6) RPE
Note;
• Thin foveal layers and compact cone photoreceptor
helps to form sharpest vision and steoropsis
• Foveal reflex is caused by the parabolic shape formed
by the clivus.
• Loss of foveal reflux implies disruption of neural layers

8. Around the optic cup is neuroretinal rim
• Pink and sharp peripheral margin
• Contain nerve axon
• Broad inferior rim followed by superior> nasal>temporal ( ISNT rule)
• Optic disc is important landmark in retina
• The site where ganglion cell axons accumulate and
exit the eye
• The optic disc lacks all retinal elements except the
nerve fiber layer and an internal limiting membrane
• Vertically oval Vertical diameter-1.8mm Horizontal
diameter- 1.5 mm
• Anterior posterior width- 0.7-1mm in length
Pale center area-physiological cup
• Horizontally oval
• Free of nerve axon(cup)-0.3mm
• Normal CDR= 0.4
OPTIC DISC- SURFACE ANATOMY
Inferior
superior
Nasal temporal

9. • Optic disc contains no photoreceptor cells light incident
on the disc does not elicit a response; thus it represents
the physiologic blind spot.
• It is paler than the surrounding retina because there is
no RPE.
• The pale-yellow/salmon color of disc is due to
combination of the scleral lamina cribrosa and the
capillary network.
PAPILLEDEMA is edema of the optic disc secondary to an
increased in intracranial pressure (ICP).
• pressure within the meningeal sheaths causes fluid to
accumulate within the fibers so that they swell leading
to blurring of the disc margins
• Edema of the optic disc from any other cause is
referred to as simply “edema of the optic disc.”
CLINICAL CORRELATES- OPTIC DISC

10. PR is divide into four parts
1. Near periphery
• (1.5mm around the macula )
2.Mid-periphery
• (3mm around the near periphery )
3.Far periphery
• Extends 9-10 mm from optic disc on
the temporal side and
• 16 mm on the nasal side in the
horizontal meridian
4.Ora serrata.
PERIPHERAL RETINA (PR)
5.5mm
Macula
1.5mm
3mm
9-10mm16mm
• Anatomical equator is located approximately 2DD from the entrance of
vortex vein/about 24mm from the center of optic disc

11. ORA SERRATA
Normal variant of Ora serrata
• Oral bays- scalloped edges of pars plana between dentate
processes
• Dentate processes- teeth like extension of retina into pars
plana
• Enclosed oral bays- island of pars plna surrounded by
retinal tissue, can be mistaken for retinal hole
• Granular tissue- white opacity withion the vitreous
base(yellow circle), can be mistaken for peipheral opercula
• Meridional fold- thickened retinal tissue
It is transition zone between retina and par plana
Description Length
Width of ora serrata 2.1mm temporally
0.7-0.8mm nasallly
Location from limbus 6mm nasally
7mm temporally
From equator 6-8mm
From optic disc 25 mm nasally

12. Implication-
1. Posterior Vitreous detachment may case tractional retinal detachment
2. Blunt trauma may cause avulsion of thin ora serrata and vitreous base
and tearing of pars plana and anterior border of retina
• Vitreous base is 3-4mm wide stradding
the ora serrata
• Vitreous is strongly adhered at
vitreous base
CTN….

13. RETINAL MICROANATOMY
Retina is composed of 10 micro layers (Sclerad to vitread)
Retinal pigment epithelium;
Photoreceptor layer of rods and cones;
External limiting membrane;
Outer nuclear layer;
Outer plexiform layer;
Inner nuclear layer;
Inner plexiform layer;
Ganglion cell layer;
Nerve fibre layer;
Internal limiting membrane.
Neuron 1
( perception
elements )
Neuron 11
(conductive and
associative
elements)
Neuron 111
(conductive
elements )

14. • In far periphery it continues forward as the pigmented layer of the ciliary epithelium
• A single layer of outermost cuboidal epithelial
cells of the retina
• Located between the highly vascular
choriocapillaris and the outer segments of
photoreceptor cells
• 4- 6 million RPE cells per eye.
• Extends from the optic disc to the ora serrata,
RPE
RPE
Bruch’s
membrane
Choriocapillaries
Photoreceptor
layers

15. RPE are Cuboidal cells with three Cell Surfaces characteristics;
Clinical coorelates;
• No specialized junctional complex between RPE and
photoreceptors- loosely adhered
• Creates potential space( subretinal space- prone for RD)
RPE- ULTRASTRUCTURE
Apical surface
• Has microvillous processes- Increases Surface area
• Interdigitate with outer segments of photoreceptor cells
• Contains melanin granules – more in macular region
1.Apical surface –inner surface
2.Paracellular surface-intercellular surfaces
3.Basal surface – outer surface

16. Paracellular surface;
• Contains tight junction( Zonula Occluden & adheran, gap junctions)
• Junctional complex form blood-retinal barrier
• Maintains retinal homeostasis and prevents from toxic damages
RPE- ULTRA STRUCTURE
Basal surface;
• Attached to its basal lamina, the
lamina vitrea of Bruch's membrane.
• Nutrients from choriocapillaries
difusess to RPE through basal
lamina

17. RPE- FUNCTION
• Visual pigment regeneration
• Phagocytosis of shed photoreceptor outer-segment discs
• Transport of necessary nutrients and ions to photoreceptor cells and
removal of waste products from photoreceptors
• Absorption of scattered and out-of-focus light via pigmentation
• Adhesion of the retina
• Synthesis and remodeling of the interphotoreceptor matrix,
• Formation of the blood-retina barrier,
• Elaboration of humoral and growth factors.
Clinical notes
• Failure of the RPE to process cellular debris associated with outer segment turnover
cause deposition of Drusen in ARMD
• Disruption of blood retinal barriers causes retinal edema eg. Macular edema

18. PHOTORECEPTOR LAYERS
Density and distribution of photoreceptors
Cones- Rods
- 4.6 million - 92 million
- density is maximum at fovea - maximum density in 20°(3mm) from the fovea
(199 000 cones/mm2) (160,000 rods/mm2)
-minimum density- periphery - rod-free at the fovea ; 0.35 mm
-minimum density- periphery
- light sensitive molecule- Iodopsin - light sensitive molecule- rhodopsin
( color vision-photopic vision) ( night vision- scotopic vision)
( 3 types of iodopsin- trichromatic pigments - rhodopsin is sensitive to blue-green light- 493nm
1. S wavelength cones- 440nm blue light)
2.M wavelenght cone- 540nm green
3. L wavelenght cone- 577nm red
Clinical notes-
• Mutation of rhodopsin in retinitis pigmentosa causes maximum pigmentation 3mm around the
fovea
• With advanced of age there is progressive loss of photoreceptors (rods are affected more than
cone)- poor night vision in elderly

19. MORPHOLOGY OF PHOTORECEPTORS
Rods and cones are composed of several parts- 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

21. STRUCTURE OF ROD CELL:
1. 40-60 µm long.
2. Outer segment is cylindrical- contains visual pigments
3. Pigments are located in flattened double lamellae in the form
of discs.
4. Discs various between 600 to 1000/rod cell. There are no
special attachments bet. discs or bet. discs and plasma
membrane.
5. Discs contain 90% of the visual pigment remaining is
scattered on plasma membrane.
6. Inner segment of the rod is thicker than the outer. It has two
regions.
a. Outer eosinophilic ellipsoid which contains more
mitocondria.
b. Myoid which contains glycogen as well as usual
organelles
Clinical notes;
• Rod need great sensitivity to detect the small amount of light available
• Rod are numerous and contains a bout a million rhodopsin molecule in each sac/disc

22. CTN…
• The rhodopsin molecule is
composed of protein called opsin
and chromophore (aldehyde of
Vitamin A- 11-cis-retinal)
• Opsin protein is embedded in the
lipid membrane lamellar discs
• Opsin is made up of amino acids
• It has 7 helical loops.
• At 7th helical loop 11-cis-retinal
is attached lysine by a protonated
Schiff base linkage- molecular
antena!
Clinical notes
• Chromophore and opsin forms molecular antenna which transform single quantum of light
into electrical energy ( action potential ) process called phototransduction
• it is accomplished within the outer segments of the photoreceptors − the rods and cones
• Lack of vitamin A causes night blindness due to defective photo pigments

23. CONES- MORPHOLOGY
1. Conical in shape
2. 40 TO 80 µm long
3. Cone at periphery is short but in central fovea it is
tall and resembles rod
4. Outer segment contains photo pigments called
iodopsin.
5. The cone outer segment have more discs (1000-1200 per
cone) than do rod outer segments
6. Lamellar disc are attached to the membrane
1. Inner segment is similar to rod structures.
2. Ellipsoid contains a large number of mitochondria.

24. • Not a true membrane
• Composed of the terminal bars
(zonulae adherentes) between
Muller cells and photoreceptors
• Fenestrated membrane
• Extents from the ora serrata to
the edge of optic disc.
Main function-
• Selective barrier for nutrients
• Stabilization of transducing
portion of the photoreceptors.
OUTER NUCLEI LAYER(ONL)
• Formed by nuclei of rods and cones.
• Rod nuclei form the bulk of this layer.
RPE
ELM
EXTERNAL LIMITING MEMBRANE .
ONL
Muller cells

25. OUTER PLEXIFORM LAYER:
• It marks the synaptic junction of
photoreceptor and second order neurons
in retina( between ONL and INL)
• The outer plexiform layer is thickest at
the macula
• In the fovea there is no synaptic
terminals, because cone pedicles are
displaced laterally to the extrafoveal
region.
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- eg.dark maroon dot and blot
hemorrhage in deep retinal hemorrhage

26. Cone pedicle are pyramidal in shape with three type of neuronal axon/processes ( triad arrangement)
1. Central axons of midget bipolar cell that may contact the same cone at 10-25 different points.
2. Two dendrites on either side of the triad which originates from different horizontal cells
• Have total synaptic complex of 25 per pedicle which helps to spread light excitation over a large
portion of the connections in the outer plexiform layer
• Synaptic terminal are formed by the photoreceptor
terminal and the dendritic processes of INL cells
• The rods has a round or oval cytoplasmic
expansions called spherules with few synaptic
terminals
• Cone have larger cytoplasmic expansions known as
pedicles with multiple synaptic terminals
Two type of dendritic processes contact with spherules
1. One Deep horizontal cell axon
2. 1-4 Shallow bipolar cell axon
(this form total synaptic complex of 2-7 per spherules)
PHOTORECEPTOR SYNAPTIC TERMINAL

27. Located betweeen OPL and IPL
Consists of following 8-12 rows of cells:
• Bipolar cells- 9 types
• Horizontal- 3 types(H1,H11,H111)
• Amacrine
• Supportive Muller’s cells
Four layers can be distinguished by light microscopy
1. Outermost layer -horizontal cell nuclei
2. Outer intermediate layer- bipolar cells
3. Inner intermediate layer -Muller cell
4. Innermost layer-amacrine and interplexiform cell nuclei.
INNER NUCLEATED LAYER
Numerous cells and extensive cellular connection of INL is essential for transduction and
amplification of light signals.

28. Horizontal cells
• Flat cells,
• Has numerous neuronal
interconnections between photo
receptor and bipolar cells in the outer
plexiform layer.
• highest concentration in fovea
• Their processes branch extensively as one
proceeds from the central retina towards
the ora serrata.
• This arrangement expands the receptive
field of the photoreceptors beyond their
dendritic field.
HORIZONTAL CELLS
Function-
• Modulate and transform visual information received from the
photoreceptors

29. HORIZONTAL CELLS
Divided into 3 types
1. HI
• Has stout dendrites that connects only cones at traid and
rod spherules
• The HI cells connects more with L-cone and M-cones
2.HII
• The HII cells have slim overlapping dendrites and a short
curved axon
• Connects all types of cones
3.HIII
• The Hlll cells are 30% larger than the HI cells and contact
more cones, but are otherwise similar with H1
Specific Functions-
• HI cells connects longer wavelength cones and functions as luminosity cells- enhances visual clarity
• HII types connects shorter wavelength cones and act as chromaticity cells- enhances color vision

30. BIPOLAR CELLS- 2ND ORDER NEURON
• Oriented radially in the retina
• Located in the inner nuclear layers
and their processes extend to the
outer and inner plexiform layers
• Receive extensive synaptic feedback
from amacrine cells
Function-
• Bipolar cells relay information from photoreceptors to horizontal,
amacrine, and ganglion cells .

31. Under light microscopy nine types
a. Rod bipolar cells(RB)
b. Invaginating midget bipolar(7) –
smallest(MB)
c. Flat midget bipolar
d. Invaginating diffuse bipolar
e. Flat diffuse bipolar
f. On-centre blue cone bipolar
g. Off-centre blue cone bipolar
h. Giant bistratified bipolarGBB)
i. Giant diffuse invaginating bipolar
Rod bipolar interacts only with rod photoreceptor rest contacts with cones
There are about 35.68 million Bipolar cells in retina with highest concentration at fovea
Number & Axonal complexity for- Amplification and modulation of visual perception
BIPOLAR CELLS – 2ND ORDER NEURON

32. CNT…
Clinical application;
• The OFF bipolar depolarizes in dark and hyperpolarizes in light- activated by cones
• The ON bipolar depolarizes in light and hyperpolarizes in dark- activated by rods
• Bipolar cells transfer information to retinal ganglion cells, which are the first cells in the visual
pathway to respond with an action potential
• Bipolars cells which respond with
depolarization(inactivation) are OFF bipolars
• Bipolar cells which respond with hyperpolarization
(activated state) called are ON bipolars.
• OFF bipolars synapse in the outer part of the IPL
• ON bipolars synapse in the inner tier, closest to the
ganglion cell layer

33. AMACRINE CELLS
Amacrine cells are flusk/urn shape cell located in inner
nucleated layer close to the inner plexiform layers
Upto 24 varieties has been described but two major types are
based on their characteristics;
1. Diffuse Amacrine cells (A11)
• processes extend throughout the entire inner plexiform
layer
• Further subdivided into narrow, medium, or wide field
types, depending on the width covered by their axonal
fields
2. Stratified Amacrine cells(A)
• fibers run in the outer half of the inner plexiform layer
The remarkable feature of amacrine cells is the broad distribution of their axonal processes through all
strata of the inner plexiform layer
• Amacrine cell processes indicates that these cells play an important role in the modulation of electrical
information reaching the ganglion cells

34. • Consists of synapses bet. Axons of bipolar
cells and dendrites of ganglion and
amacrine cells.
• Two elements are present at synapse in an
arrangement that is known as a 'dyad‘
• In this type of synapse, the bipolar cell
contracts two processes, one from a
ganglion cell and the other from an
amacrine cell
INNER PLEXIFORM LAYERS
Two distinct synapses are unique to the amacrine cells in IPL:
1. The reciprocal synapse
• Connecting amacrine cell synapse back to the nearby bipolar cell terminal, suggesting a local feedback
mechanism between these cells.
2.The serial synapse-
• Amacrine cell process synapsing with an adjacent amacrine cell process
The reciprocal
synapseSerial synapse

35. Ganglion cells transmits signal from the bipolar cell to the lateral geniculate
body
1.2 million ganglion cells are present in the retina each with a single
axon
• 3rd order neuron of ganglion
cells lie in this layer.
• Single row in Peripheral retina
• At the adge of foveola (macula)
it is multi layer(6-8 layered) and
on temporal side of disc it has
two layers.
• It is absent in foveola and optic
disc
GANGLION CELL LAYERS-

36. CTN..
1.P ganglion cells- The midget cells
• Monosynaptic ganglion cells, show dendrites that
synapse exclusively with axon terminals of midget
bipolar cells and amacrine cell processes
• P cells are concentrated in central retina,
• Constitute 80% of the ganglion cell population.
2.M ganglion/Paasol cells-polysynaptic•because they
make synapses over a wide area.
• They synapse with all types of bipolar cells except the
midget bipolars
• M cells constitute 5% of the total ganglion cell
population at the fovea and 20% at the periphery of
the retina
18 types of ganglion cells described- two main types are

37. CTN…
P Ganglion cells
• The P ganglion cells project to the
parvocellular layers
• P cells seem to be specialized cells in
primates for color vision
M ganglion cells
• M ganglion cells projects to
Magnocellular layers of LGN
• M cells have expansive processes and cover a large area of retina, they can
respond rapidly to moving or changing stimuli.
• Sensitive to luminance changes in dim illumination (scotopic conditions)

38. NERVE FIBER LAYERS
• The nerve fibre layer contains the
axons of the ganglion cells
• Optic nerve consists of approximately
1.2- 1.5 million axons of retinal
ganglion cells
• Their course runs parallel to the retinal
surface
• The fibers proceed to the optic disc at a right angle, and exit the eye
through the lamina cribrosa as the optic nerve.
• The fibers generally are unmyelinated within the retina

39. ARRANGEMENT OF NERVE FIBRES IN THE RETINA
1. Fibres from the nasal half of the retina come
directly to the optic disc as superior and
inferior radiating fibres (srf and irf).
2. Fibres from the macular region pass straight
in the temporal part of the disck as
papillomacular bundle (pmb).
3. Fibres from the temporal retina arch as
superior and inferior arcuate fibres (saf and
iaf).
• The nerve fibre layer is thickest at the nasal edge of the disc, where it measures 20-30
microns
• The thickness decreased with increasing distance from the disc margin, becoming 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

40. ARRANGEMENT OF NERVE FIBRES OF THE OPTIC
NERVE HEAD:
• Fibres form the peripheral part of the retina lie deep in
the retina but occupy the most peripheral part of the
optic disc.
• While the fibres originating closer to the optic nerve
head lie superficially in the retina and occupy a more
central (deep) portion of the disc.
THICKENSS OF NERVE FIBRE LAYER AT THE DISC:
• Thickness of the nerve fibre layer around the different quadrants of the optic disc
margin progressively increases in the following order:
1. Most lateral quadrant (thinnest)
2. Upper temporal and lower temporal quadrant
3. Most medial quadrant
4. Upper nasal and lower nasal quadrant (thickest)

41. CLINICAL SIGNIFICANCE OF DISTRIBUTION AND THICKNESS OF
NERVE FIBRES AT THE OPTIC DISC MARGIN:
1. Papilloedema appears first of all in the thickest quadrant (upper nasal
and lower nasal) and last of all in the thinnest quadrant (most lateral).
2. Arcuate nerve fibres are most sensitive to glaucomatous damage,
accounting for an early temporal arcuate visual scotoma in glaucoma
3. Macular fibres occupying the lateral quadrant are most resistant to
glaucomatous damage and explain the retention of the central vision till
end.
The loss of tissue seems to be associated with compaction and fusion of the laminar
plates . It is most pronounced at the superior and inferior poles of the disc

42. INTERNAL LIMITING MEMBRANE
• The internal limiting membrane forms the innermost layer
of the retina and the outer boundary of the vitreous
• Both the retina and the vitreous contribute to the formation
of this membrane.
• Consists of four elements:
(1) collagen fibrils and
(2) proteoglycans (mostly hyaluronic acid) of the vitreous;
(3) the basement membrane;
(4) the plasma membrane of the Muller cells and possibly
other glial cells of the retina
• In the posterior retina the internal limiting membrane attains a thickness of 0.5-2.0 Um.
• 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

43. THANK YOU

44. REFERENCES
• Wolff's ANATOMY OF THE-EYE AND ORBIT , 8th edition
• AAO, section 2 fundamental and section 12
• LEE and Remington- clinical anatomy and physiology of visual system-3rd edition
• Yanoff and Duker- Ophthalmology- 3rd edition
• Images and graphics- internet sources