Anatomy and Physiology of retina

1. ANATOMY OF
RETINA
MODERATOR : DR MANOJ SASWADE
PRESENTOR : DR VIVEK ADWE

2.  DEVELOPMENT OF RETINA
 GROSS ANATOMY
 MICROSCOPIC STRUCTURE
 BLOOD SUPPLY OF RETINA

3. Retina is the innermost tunic of eyeball.
Thin (200 micron) , transparent membrane.
Continuous posteriorly with the optic nerve, while anteriorly with the
ciliary body & iris epithelium.
Bordered by the vitreous internally & the Bruch’s membrane externally.
Firmly attached at the margins of optic disc and at its anterior termination
at the ora serrata .

5. DEVELOPMENT
It is developed from the 2 parts of optic cup
Inner layer neurosensory retina
Optic cup ---
Outer layer Retinal pigment
epithelium

7. GROSS ANATOMY
Extent : Optic disc to ora serrata. Surface area : 266 sqmm.
posterior pole --- 0.56 mm
Thickness equator -------- 0.18- 0.2 mm
ora serrata ----- 0.1 mm
Regions
Optic disc Macula lutea Peripheral retina

8. • OPTIC DISC
Pale pink, well defined circular area.
1.5-1.8 mm diameter
At Optic disc all the retinal layers terminate except Nerve Fibre Layers
In the centre nerve, fibres are thinnest hence lamina shines brightly. The grey
spots in lamina when seen are due to non medullated nerve fibres reflecting less
light than white connective tissue
Blurring of margins with swelling- Disc edema; Unilateral/Bilateral.
 Physiological Cup of Optic disc: depression seen in the disc
The cup varies in size, shape, position and depth in different eyes.
Central retinal vessels emerge through the cup.

9. MACULA LUTEA
= Yellow spot
-(Oxygenated carotenoids – Lutein , Zeaxanthine
-antioxidant properties filter blue wavelengths of light – prevents photopic damage)
Temporal to optic disc, 5.5 mm in diameter situated at posterior pole between the
temporal vascular arcade
= 15 degree of visual field
Primary function: Colour vision and Photopic vision.
Macula lutea mainly comprises of following areas
• Foveola
• Fovea
• Parafovea
• Perifovea

11. Umbo : tiny depression in the centre of foveola --- foveal reflex
Diameter : 150-200 microns.
Thin foveal layers and compact cone
photoreceptor helps to form sharpest
vision and stereopsis
Foveal reflex is caused by the reflection
of light form walls of foveal pit
Loss of foveal reflex implies
disruption of neural layers

12. • Foveola
• central floor of fovea.
• 2 DD away from temporal edge of Disc and 1 mm below horizontal
meridian.
• Diameter :0.35mm, thickness 0.15 mm.
• Fovea
Central depressed part of Macula a/k/a Fovea centralis.
Corresponds to 5 degree of visual field.
Diameter 1.5 mm, thickness 1.5 mm.
Thus Fovea represents the excavation in retinal centre and consists of a
margin k/as Margo fovea , ring like reflection of internal limiting
membrane.

13. Parafovea
0.5 mm belt that surrounds foveal margin : 4-6 layers of ganglion cells, 7-11
layers of bipolar cells
Perifovea
1.5 mm that surrounds parafoveal area.
Several layers of ganglion cells, 6 layers of bipolar cells
Foveal Avascular Zone-FAZ
0.5mm
FA, OCTA- Structural vs Functional FAZ
FAZ dimensions strongly positively correlate with capillary non perfusion over
post.pole

14. • PERIPHERAL RETINA
Near periphery : 1.5 mm circumscribed region around area centralis.
Mid periphery : 3 mm zone around near periphery. Outer limit
correspondes to equator.
Far periphery : equator ---- ora serrata. Width varies depending on ocular
size and refractive error. Average width 6 mm
average circumference : equator – 72 mm , ora serrata – 60 mm.
Extreme periphery : area of ora serrata and pars plana.

16. • ORA SERRATA
• It is a serrated peripheral margin where retina ends and ciliary body
starts.
• Oral bays- post extension of pars plana towards retinal side
• Dentate processes- teeth like extension of retina into pars plana
• Enclosed oral bays- dentate processes may wrap around a portion of ora
bay to form enclosed ora bay. May be mistaken for retinal hole
• Granular tissue- white opacity within the vitreous base(yellow circle),
can be mistaken for peripheral opercula
• Meridional fold- thickened retinal tissue extended into pars plana. MC
in supero-nasal quadrant

17. • ORA SERRATA
• enclosed ora bays
ora bays dentate
process
meridional fold granular tissue

18. At ora serrata sensory retina is firmly attached both to vitreous and retinal
pigment epithelium
Width : 2.1mm temporally
0.7-0.8 mm nasally
Location from limbus: 6 mm nasally, 7 mm temporally
6-8 mm away from equator and 25 mm from Optic nerve on nasal side
Ora serrata is watershed zone between anterior and posterior vascular
systems
Vitreous base is 3-4mm wide stradling the ora serrata
Vitreous is strongly adhered at vitreous base

19. 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

20. MICROSCOPIC STRUCTURE

21. 1.) RETINAL PIGMENT EPITHELIUM
1. Outer most layer, consists of single layer of hexagonal shape cells
2. It is firmly attached to underlying Bruch’s membrane and loosely
attached to layer of rods and cones.
3. Space bet. RPE and sensory retina is called sub retinal space.
Separation of RPE from sensory retina is called retinal detachment.
4. On electron microscopy the adjacent RPE cells are connected with
each other by tight junctions( Gap junctions , zona oclludens and zona
adherens) and constitute the outer blood retinal barrier
5. Zona oclludens forms the external component of the Blood retinal
Barrier.
6. Rest of intercellular space is filled by Extra cellular matrix.

22. RPE CELL
A single layer of outermost hexagonal Bruch’s membrane
cuboidal epithelial cells of the retina Rpe chorio-
Located between the highly vascular capillaries
choriocapillaris and the outer segments
of photoreceptor cells
4- 6 million RPE cells per eye. photoreceptors
Extends from the optic disc to
the ora serrata,

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

24. FUNCTIONS OF RPE
Important role in photo receptor renewal and recycling of Vit.A.
Maintain integrity of subretinal space by forming the outer blood retinal
barrier
Absorption of scattered light by Melanin Granules.
Transport of nutrients and metabolites through outer blood retinal barrier.
Inter photo receptor matrix participates in retinal attachment of the retina
to RPE and facilitates Phagocytosis of the shed discs of the outer cone
segments.
On the basal surface RPE cells produce type 4 collagen, heparin sulphate
and laminin which become incorporated in lamina vitrea of Bruch’s
membrane.

25. • LAYER OF PHOTO RECEPTORS
There are about 120 million rods and 6.5 million cones.
End organs of vision which transform light energy to visual impulse.
Rods contain photo sensitive substance rhodopsin which is responsible for
peripheral vision and vision of low illumination.
Cones contain iodopsin responsible for central vision and colour vision.
Highest density of cones is at fovea.
Rods are absent at fovea and are maximum below the optic disc.

26. ROD CELL
40-60 µm long.
Outer segment is cylindrical. It contains flattened
double lamellae in the form of discs.
No. of Discs varies between 600 to 1000/rod cell.
Discs contain 90% of the visual pigment
remaining is scattered on plasma membrane.
Inner segment of the rod is thicker than the outer.
It has two regions. Outer eosinophilic ellipsoid
which contains more mitocondria.
Inner Myoid which contains glycogen as well as
usual organelles

27. CONE CELL1.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
7.Inner segment is similar to rod structures.
8. Cone Ellipsoid contains a large number of
mitochondria than rods.

28. EXTERNAL LIMITING MEMBRANE
• Not a true membrane
• Composed of the terminal bars (zonulae
adherentes) between Muller cells and
photoreceptors
• Appears as Fenestrated membrane
• Extends from the ora serrata to the edge of
optic disc.
Main function-
• Selective barrier for nutrients
• Stabilization of transducing portion of the
photoreceptors.

29. OUTER NUCLEAR LAYER
• Formed by nuclei of rods and cones.
• Rod nuclei form the bulk of this layer.
• No. of rows of nuclei and thickness of
this layer varies from region to region-
Nasal to disc-8-9 layers and 45micron
thickness
• Temporal to disc-4 layers and 2
2 micron thickness
• In foveal region (thickest)- 10 layers
and 50 micron thickness

30. OUTER PLEXIFORM LAYER
It marks the synaptic junction of
photoreceptor and first order
neurons in retina( between ONL and
INL)
The outer plexiform layer is thickest
at the macula.
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.

31. Clinical significance
Hard exudates
-Formed in outer plexiform layer by deposition of lipid and lipo-proteins.
-results from abnormal vascular permeability of retinal or sub-retinal vessels.
Haemorrhage
-The dark maroon dot and blot hemorrhage in deep retinal hemorrhage are
found in this layer.

32. INNER NUCLEAR LAYER
Consists 8-12 rows of following
cells:
 Horizontal- (outermost layer)
 Bipolar cells (outer intermediate)
 Supportive Muller’s cells (inner
intermediate)
 Amacrine cells (innermost)

33. BIPOLAR : 1ST ORDER NEURONS
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 .
Bipolars cells which respond in dark state are OFF bipolars.
depolarization(inactivation). They synapse in the outer part of
IPL. Off bipolars are activated by cones
Bipolar cells which respond in presence of light with
hyperpolarization (activated state) called are ON bipolars.
They synapse in the inner tier near the ganglion cell layer
On bipolars are activated by rods

34. HORIZONTAL CELL
Flat cells.
Highest concentration in fovea
Their processes branch extensively as one proceeds
from the central retina towards the ora serrata thus
expanding the receptive field
Function-
Modulate and transform visual information horizontal
received from the photoreceptors cell
Type A cell: 7 group of dendrites --- triad of 7 cone pedicles
Type B cell: 7 group of dendrites--- rod receptors only

35. AMACRINE CELLS
Amacrine cells are pyriform shaped cell located in inner
nuclear layer close to the inner plexiform layers
These form connections with the axons of bipolar cells
and dendrites and soma of ganglion cells.
The remarkable feature of amacrine cells is the broad
distribution of their axonal processes through all strata
of the inner plexiform layer
an important role in the modulation of electrical
information reaching the ganglion cells

36. MULLER CELLS
• Major glial cells ;
• Stretching across thickness of retina.
• Homeostatic and metabolic support to neurons.
• Nucleus and cell bodies are within the inner nuclear layer.
• By uptake of glutamate, directly involved in regulation of synaptic activity.
• Subset of muller cells may differenciate into progenitor/stem cells. (development of
new therapeutic approach)

37. INNER PLEXIFORM
LAYER
Consists of synapses bet. Axons of bipolar
bipolar cells (1st order) and dendrites of ganglion (2nd order)
and amacrine cells
and Two distinct synapses are unique to the amacrine
cel cells in IPL:
1. 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

38. GANGLION CELL LAYER
2nd order neuron of ganglion cells lie in this layer. Single row in Peripheral retina
• At the edge 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
P ganglion cells- The midget cells (80% population)
• 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. They project to Parvocellular layer
M ganglion/Parasol cells- polysynaptic•. They synapse over 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
• They project to magnocellular layer

39. NERVE FIBRE LAYER
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
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 retina
Cotton wool spots
• white fluffy patches that lie in nerve fibre layer
• Occur in diseases causing micro vascular ischemia like:
Diabetes, HTN, SLE & venous infarcts.
Nerve fibre layer hemorrhages
linear, flame shaped due to tracking along the axons

40. ARRANGEMENT OF
NERVE FIBRE LAYERS
 Fibres from the nasal half of the retina come
directly to the optic disc as superior and inferior
radiating fibres (srf and irf).
 Fibres from the macular region pass straight in the
temporal part of the disc as papillomacular bundle
(pmb).
 Fibres from the temporal retina arch above &
below macular & pmb as superior and inferior
arcuate fibres (saf and iaf).
NFL is thickest at the nasal edge of the disc, where
it measures 20-30 microns
The thickness decreases with increasing distance
from the disc margin, becoming 8 to 11 microns just
posterior to the ora serrata.

41. • Arrangement of NFL
Fibres from 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.
CLINICAL SIGNIFICANCE
Papilloedema : 1st at thickest quadrant (upper and lower
Nasal quadrant)
Glaucomatous damage : Arcuate fibres (most sensitive)
early temporal arcuate visual scotoma.
Macular fibres occupying the lateral quadrant (most resistant)
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 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 (2) proteoglycans (most hyaluronic acid)
(3) the basement membrane; (4) the plasma membrane of the Muller cells
• In the posterior retina : thickness of 0.5-2.0 microns.
• 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. BLOOD SUPPLY OF RETINA
Outer 4 layers of retina (till outer nuclear layer) is supplied by choriocapillaris.
The inner six layers gets its supply from central retinal artery which is a branch
of ophthalmic artery.
The outer plexiform layer is the water shed area with dual blood supply
The fovea is avascular and is mainly
supplied by choriocapillaris.
Two capillary networks :
Superficial – lies at the level of NFL
Deep – lies between inner nuclear and
outer plexiform layer

44. BLOOD RETINAL BARRIER
• Outer – tight junction between RPE cells.
• Inner – endothelial cells of retinal capillaries are bound closely by intercellular
junction of zonula occludens - thus prohibiting free flow of fluid and solutes.
• These endothelial cells are encircled by
a layer of pericytes & basement membrane.
• Retinal blood vessels lack an internal elastic
lamina & a layer of smooth muscle cells.
• The retinal arteries are end arteries & have
no anastomosis. The only place where the retinal
system anastomoses is in the neighbourhood of
lamina cribrosa.

45. 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.

46. PHYSIOLOGY OF VISION
Main mechanism concerned with
vision :-
• 1)Transduction
• 2) Transmission of visual
sensation
• 3) Visual perceptions

47. • 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

48. 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)

49. 11 CIS
RETINA
L
Light
All Trans
Retinal
This process is known as photodecomposition
and rhodopsin is said to be bleached.

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

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

52. 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

53. 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.

54. VISUAL
PERCEPTION
Stimulation Sensation
1.Light sense
2. Form Sense
3. Sense of contrast
4. Colour sense

55. • 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.

56. • 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.

57. • 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

58. • 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)

59. 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

60. VISUAL PATHW
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

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

64. THANK YOU