The document discusses the anatomy and physiology of the retina. It begins by describing the embryological origin and topography of the retina. It then describes the major anatomical structures in detail, including the optic disc, macula lutea, fovea, and layers of the retina. The microscopic architecture contains 10 layers arranged from the sclerad to the vitread side. The physiology section briefly outlines the process of phototransduction and visual signal transmission through the retina and visual pathways.

1. ANATOMY OF RETINA
PHYSIOLOGY OF VISION
VISUAL PATHWAYS
Dr. Sajjan Sangai
Dept. of Ophthalmology
MGM Medical College and Hospital

2. Embryology
• Structures that are derived from the optic
vesicle
Sensory layer of retina (Pars optica retinae)
Epithelial linings of cilliary body/iris (Pars
retinae cilliaris/ Pars retinae iridis)

3. Topography of Retina
• Diaphanous tissue: Purplish / red due to visual
pigment (rhodopsin).
• Most highly developed tissue of the eye.
• Extends from the optic disc to ora serrata.
• Surface area: 266 mm2
• Thickest near optic disc :0.56 mm
• Thinner towards periphery: 0.18 mm - Equator
0.10 mm - Ora

4. Retinal Equator
• Retinal Equator – Line where 4 vortex veins
exit , retina posterior to this is known as
posterior retina.

5. Retina
Optic Disc
Macula lutea
Peripheral Retina

6. 1. Optic Disc

7. • Colour :Pale pink
• 1.5 mm diameter, well defined circular area
• At the optic disc- All retinal layers terminate
except nerve fibres , which pass through the
lamina cribrosa to run into optic nerve.
• Physiological Cup: Depression seen in it ,
central retinal vessels emerge through the
centre of this cup.

8. 2. Macula Lutea/ Area Centralis
• Yellow spot – due to presence of carotenoid
pigment Xanthophyll.
• Dark area : 5.5 mm in diameter
• Situated in posterior pole of the eyeball ,
temporal to optic disc.
• Corresponds to 15 degrees of the visual field ,
accurate diurnal vision and colour
discrimination are primary functions.

10. Fovea
• Approximate centre of area centralis
• Posterior pole of globe
• 3-4mm temporal to the centre of optic disc.
• 0.8mm below horizontal meridian.
• Diameter-1.85mm – 5 degrees of visual field
• Avg. thickness- 0.25 mm

11. • Central concave indentation – Foveola is
produced.
• Downward sloping border which meets the
floor of foveal pit is known as CLIVUS.
• UMBO: Tiny depression in very centre of the
foveola ( Visible foveolar reflex on Direct
Ophthalmoscope).

12. Foveola
• Diameter: 0.35mm
• Thickness:0.13mm
• Highest visual acuity in retina corresponds to
only 1 degree of visual fields due to
I. Sole presence of cone photoreceptors.
II. Avascular nature.
• Foveal Avascular Zone: Located inside fovea
but outside foveola (clinically can be rendered
on FFA).

13. 3. Peripheral Retina
• Increases the field of vision
• Divided into 4 regions
I. Near periphery-1.5mm around area centralis
II. Mid periphery- 3mm wide zone around near
periphery
III. Far periphery- from optic disc- 9-10 mm on
temporal side and 16 mm on nasal side in
the horizontal meridian(asymmetry due to
optic disc on nasal side)
IV. Ora serrata

14. Ora serrata
• Serrated peripheral margins where the retina
ends and cilliary body starts.
• 6mm nasally- 7mm temporally from limbus.
• 6-8 mm from limbus
• 25mm from optic nerve on nasal side

15. Ora serrata

16. Microscopic Architecture of Retina
• Contains 3 types of cells and their synapses
arranged in following layers: (Sclerad to
Vitread) are as follows:

17. Retinal Pigment Epithelium
Photoreceptor cell layer
External limiting membrane
Outer nuclear layer
Outer Plexiform layer
Inner nuclear layer
Inner Plexiform layer
Ganglion cell layer
Nerve fibre layer
Internal limiting membrane

18. Retinal Layers

19. Layer Degree of neurons
Pigment epithelium Neuroepithelial layer
Photoreceptor layer Neuron I (rod and cones)
Ext. limiting membrane (Percipient Elements)
Outer nuclear layer
Outer plexiform layer
Inner nuclear layer Neuron II Cerebral Layer
Inner plexiform layer Conductive and
associative elements
( Bipolar cells, Horizontal
cells, Amacrine cells ,
Centrifugal bipolars,
Ganglion cell layer Neuron III Muller fibres,
Nerve fibre layer conductive elements Astrocytes.)
Internal limiting membrane

20. I. Retinal Pigment Epithelium
• Fine mottling due to unequal distribution of
pigmentation within individual cells, gives a
granular appearance.
• Single layer- 5 million cells , firmly attached to its
basement lamina, lamina vitrea of brusch’s
membrane.
• Cobble stone appearance ( 4.2 million – 6.1
million)
• Area centralis- 12-18 µm width, 10-14 µm height.
• Ora- 60 µm in width

21. Functions:
• Photoreceptor
renewal and recycling
of vitamin A.
• Maintain integrity of
subretinal space.
• Transport of nutrients
and metabolites.
• Mechanical support
to the processes of
photoreceptor.

22. II. Photoreceptor layer of Rods and Cones
• 77.9 -107.3 million ( avg.92 Million) Rods
• 4.08 – 5.29 million ( avg. 4.6 million ) Cones
• Arranged as mosaics with variation.
• Cone Density and Distribution:
Maximally at Fovea ( avg. 1,99,000 cones/mm2)
with increasing eccentricity from fovea , density
of cones decrease rapidly.

23. • Rod density and distribution:
Avg. Horizontal diameter of rod free area at
fovea is 0.35 mm
1.25 degrees of visual fields
Present in large number (1,60,000 / mm2) in a
ring shaped zone 5-6 mm from fovea.

24. Visual Pigments
Rods
• Scotopic vision
• Greatest sensitivity
for blue – green light (
493 nm)
• Visual Purple/
Rhodopsin.
Cones
• Trichromatic pigments
• Short-Blue- 440 nm
• Medium- Green-
540nm
• Long- Orange- 577 nm

25. • Structure of Photoreceptor (in relation to
various Layers):
Part of photoreceptor Layer
Cell body and Nucleus Outer Nuclear Layer
Cell process Outer Plexiform layer
Inner and outer segments Layer of rods and cones

26. Rod Cells
• 40-60 µm
• Cylindrical , highly
retractile ,
transversely striated
and contains visual
purple.
• Has rod spherules.

27. Cone Cells
• 40-80 µm, Largest at
fovea and shortest at
periphery.
• Contains iodopsin.
• Has cone pedicles/
cone foot.

28. III. External Limiting Membrane
• From optic disc to ora serrata and becomes
continuous with the basal lamina between the
pigmented and non pigmented portions of
cilliary epithelium.
• Functions:
1. Selective barrier for nutrients.
2. Stabilization of position of the transducing
portion of photoreceptor.

29. IV. Outer Nuclear Layer

30. • Contains: soma and nuclei of photoreceptor cells
• Width varies.
• Nasal to disc: 45 µm – 8-9 rows of nuclei.
• Temporal to disc- 22 µm – 4 rows of nuclei.
• Fovea- 50 µm – 10 rows
• Different nuclei can be differentiated because
nuclei stains with Mallory stain:
Rod nuclei forms the bulk of this multi-layered
outer nuclear layer except in foveal region
Rods Nuclei Orange
Cones Nuclei Red

31. V. Outer Plexiform Layer

32. • Synapses between rod spherules and cone
pedicles with dendrites of bipolar cells and
processes of horizontal cells
• Marks the junction of end organs of vision
and 2nd order neurons in retina.
• Thickest at macula 51 µm consists of
predominantly of oblique fibres that have
deviated from fovea also known as HENLE’S
LAYER.

33. Outer 2/3rd Layer:
Inner fibres ( Axons) of
photoreceptors.
Inner 1/3rd Layer:
Dendrites of bipolar and
horizontal cells as well as
Müller cells processes.

34. VI. Inner Nuclear Layer
• Very thin layer.
• Disappears at fovea
• Consists of :
a) Bipolar cells
b) Horizontal cells
c) Amacrine cells
d) Soma of Müller cells
e) Capillaries of central retinal arteries

35. Outermost Layer- Horizontal Cell Nuclei
Outer Intermediate Layer-
Bipolar Cell nuclei
Inner Intermediate Layer-
Muller nuclei
Innermost Layer-
Amacrine and inter plexiform cell nuclei

36. •Contribute to vertical
communication within
the retinal layer.
•Carry out paracrine
functions.
•As principal glial cells,
act as a supportive
framework and a
nutritive function.
•Synapses with the
processes of Amacrine
cells and cell bodies of the
diffuse ganglion cells.
•Neuronal
interconnections
between
photoreceptors and
bipolar cells .
Horizontal
cells
Bipolar
cells
Amacrine
cells
Müller
cells

37. • Horizontal Cell:
Flat cells having numerous horizontal
associative and neuronal interconnections
between photoreceptor and bipolar cells in
outer plexiform layer.
Unlike bipolar cells information is relayed
radially through the retina , horizontal form a
network of fibres that integrate the activity of
photoreceptor cell horizontally.

38. • Highest at fovea,
number decreases
towards periphery
but processes branch
extensively from
centre to ora.

39. • Bipolar cells:
2 Degree neuron in visual circuitry.
35,676,000 bipolar cells
Oriented radially
- Perikarya- Inner nuclear layer
- Processes- Outer/ inner plexiform layer
 9 µm at fovea, 5 µm at periphery.

40. Types of Bipolar Cells
Rod Bipolar cells
Invaginating midget
Invaginating diffuse
Flat midget
Flat Diffuse
On centre blue cone bipolar cell
Off centre blue cone bipolar cell
Giant bi-stratified bipolar cells
Giant Diffuse Invaginating

41. Bipolar Cells
Type Connections Peculiarity
1. Rod Bipolar Cells
20%, Large soma profuse
dendrites
Arborize only with rod
spherules
Axons of these bipolar cells
have synapses with soma up
to 4 ganglion cells
2. Midget Bipolar cells
Small
Make connections only in
triads of cone pedicle
Invaginating- Deeply
invaginate cone pedicle
Flat- Makes superficial contact
with cone pedicle
Axons synapses with SINGLE
ganglion cell.
3. Diffuse- Makes contact with cone
pedicles only
Not with their triads
Axons synapse with number of
ganglion cells of all types.
4. Blue cone bipolar cells Innervate more than one cone
pedicle
5. Giant Bipolar cells Distinguished by extent of
their dendritic spread

42. VII. Inner Plexiform Layer

43. • Synapses between:
Axons of Bipolar
cells
( 2nd order neurons)
Ganglion cells
( 3rd order neurons)

44. • Amacrine cells also mediate interactions
within the layer and the interplexiform cells
receive input from the Amacrine cells
• Also contains processes of Muller cells ,
abundant microvasculature , occasional
displaced nucleus of a ganglion / Amacrine
cells.
• Layer is absent at foveola
• Thicker: 18-36 µm
• More synapses per unit area >2 million /mm2.

45. VIII. Ganglion Cell Layer
• Mainly composed of cell bodies 3rd order cells.
• Others: Processes of Müller cells, other
neuroglia, branches of retinal vessels are also
present.

46. • Layer structure:
Layers Situation
Single layer Peripheral retina
2 layers Temporal side of optic disc
6-8 layers Edge of foveola
At foveola and optic nerve head, ganglion cell
layer is absent.

47. 1.2 million
ganglion cells
present in retina
Each produce a
single axon
Converge and
exit from the eye
as OPTIC NERVE

48. • Can be classified according to size, degree of
arborisation, spread of their dendrites,
pattern of synaptic connections with Amacrine
and bipolar cells.
• 2 major types:
• Project to magnocellular layer of
lateral geniculate body and exhibit
non opponent responses
M cells
(PARASOL)
• P1 – Midget cells-contribute 90% of
total ganglion cell layer @ foveola
• P2- Small Bi- StratifiedP cells

49. IX. Nerve Fibre Layer
Unmyelinated axons of ganglion cells
Converge at optic nerve head
Pass through lamina cribrosa
Become ensheathed by myelin
posterior to lamina cribrosa

50. • Contents:
1. Axons of ganglion cells- Centripetal nerve
fibre.
2. Centrifugal nerve fibre( Thicker than
centripetal).
3. Processes of Müller cells which interweave
with axons of ganglion cells .
4. Neuroglia cells present in nerve fibre.
5. Retinal vessels: Do not project on surface of
retina , rich bed of superficial capillary
network.

51. • 0.6- 2 µm non myelinated fibres.
• Contains microtubules, mitochondria, smooth
endoplasmic reticulum.

52. • Arrangement of nerve fibre in Retina:
• 1. Nasal Half: Directly to optic disc as superior
and inferior radiating fibres (Srf & Irf).
• 2. Macular region: Pass straight in temporal
part of disc as papillomacular bundle.(PMB)
• 3. Temporal retina: Arch above and below the
macular/ papillomacular bundle as superior /
inferior arcuate fibres. (Saf & Iaf).

53. • Arrangement in optic nerve:
Fibres from
peripheral part
Deep in retina
Occupy most
peripheral part
of optic disc
Fibres closer to
optic disc
Superficially in
retina and occupy
more central (deep)
portion of disc.

54. X. Internal Limiting Membrane
• Pas positive true basement membrane.
• Forms interface between retina and vitreous.
• Consists of 4 elements:
1. Collagen fibrils
2. Proteoglycans
3. Basement membrane
4. Plasma membrane
5. Plasma membrane of Müller cells and other glial
cells.

55. Retinal Layers Foveola Fovea Parafoveolar
region
Perifoveolar
region
RPE + +( Dark Area) + +
Photoreceptor
layer
C++++ C+++ C++R+ C++R+
ELM + + + +
ONL + + + +
OPL - + Thickest +
INL - + Thickest +
IPL - + + +
Ganglion cell
layer
- Multi-layered Thickest Multi-layered
Nerve fibre
layer
- + + +
Internal Limiting
membrane
+ (Thin) + + +

56. Blood Supply
• Outer four layers – Choriocapillaries
• Inner six layers- Central retina Artery
• Retina is supplied by Central Retinal Artery
Enters optic nerve on lower surface 15-20 mm
behind the globe.
Retinal arteries are end arteries and have no
anastomosis at ora serrata.

57. Arteries are distinguished from veins by being
brighter red and narrower.
Veins have purplish tint and are duller and of
wide calibre.
Choroidal vessels: Broader, ribbon like.
 Without any central streak
 Anastomose freely
 Easily visible in myopes and albinos.

59. Physiology of Vision
Initiation of vision (Photo
transduction)
Processing and
transmission of visual
sensation
Visual Perception

60. • Phototransduction:
Retina
Light falling upon
the retina causes
photochemical
changes
Photochemical changes
1.Rhodopsin
Bleaching
2. Rhodopsin
regeneration
3. Visual cycle
Electrical changes
Generation of
receptor potential

61. Rhodopsin Bleaching:
 Rhodopsin- the visual pigment present in rods
for scotopic vision.
 Maximum absorption spectrum- 500 nm
Rhodopsin
Protein- Opsin
Carotenoid- Retinine(
Vit. A aldehyde / 11
Cis Retinal)

62. 11 Cis
Retinal
Light
All Trans
Retinal
This process is known as photodecomposition and
rhodopsin is said to be bleached.

63. Rhodopsin
Bathorhodopsin
Lumirhodopsin
Metarhodopsin
All trans retinal
11 Cis retinal

64. Rhodopsin regenration:
All trans retinal +
Vitamin A ( retinal) from
blood
11 Cis Retinal + Opsin in
rod outer segment Rhodopsin

65. Visual Cycle: Equilibrium between the
photodecomposition and regeneration of
visual pigments is referred to as visual cycle.
All trans
retinal
11 Cis
retinal
Rhodopsin
Excitation of nerve
OpsinOpsin

66. Magnocellular, Parvocellular and
Koniocellular pathways
P cells/
Parvocellular
Smaller, thinner axons
of smaller calibre
Colour sensitive with
High Spatial
resolution
M cells
/Magnocelluar
Large cells, thicker,
larger axons , faster
conducting
Transmits high
temporal motion
related information of
low spatial frequency
unrelated to colour.

67. Visual Perception
Stimulation
Sensation
1.Light sense
2. Form Sense
3. Sense of contrast
4. Colour sense

68. • Light Sense:
Light falling upon retina is gradually reduced in
intensity , there comes a point when it is no
longer perceived. This is known as Light
minimum.
• Measured when eye is dark adapted for 20-30
minutes.
• Light minimum for fovea is considerably
higher than for the Para central and peripheral
parts.

69. • Form sense:
Cones play major role and most acute at fovea
where it is most closely set and highly
differentiated.
Visual acuity is measured in a variety of ways
1. Recognition- Snellen’s Chart, Landolt C chart .
2. Resolution- Acuity grating
3. Localisation- Vernier grating.

70. • Sense of Contrast:
• Ability to perceive slight change
in luminance between regions
which are not separated by
definite borders.
• Measurement of contrast
sensitivity:
1. Pelli- Robson’s Contrast
sensitivity chart.
2. Cambridge low-contrast
gratings.
3. Arden gratings.
4. Functional acuity contrast test.

71. • Colour Sense: Ability of the eye to
discriminate between colours excited by light
of different wavelengths.
Cones
Short
Stimulated by
blue light
(440nm)
Medium
Stimulated by
green light
(540 nm)
Long
Stimulated by
red light (577
nm)

72. White colour can be formed from combination
of these colours in suitable proportions hence
normal colour vision is trichromatic.
Theories of colour vision:
a) Young- Helmholtz theory
b) Opponent colour theory of Herring

73. Visual Pathway
Neural
epithelium of
rods and
cones( end
organs)
Bipolar cells
in inner
nuclear layer
with its axons
in inner
reticular layer
Ganglion cells
in retina
Optic nerve,
Chiasm to
lateral
geniculate
body
Optic
radiations to
Visual cortex

75. • Fibres from peripheral regions in retina forms
2 distinct groups corresponding to nasal and
temporal half of retina.
Fibres from
temporal half
Optic
Chiasma
Optic tract of
same side
Fibres from
nasal half
Optic
Chiasma
Optic tract of
opposite side