embryology and anatomy of retina

1. Shreeji Shrestha

2. Rete = net
Thin, delicate, transparent multilayered
sheet of neural tissue lining innermost
aspect of eyeball (photochemical
transduction occurs where nerve impulse
are created and transmitted by visual
pathway to brain)
Extends from optic disc to ora serrata
Area = 266mm2
Thickest near optic disc (0.56mm)
Equator (0.18mm)
Ora serrata (0.10mm)

3. Retina extends more anteriorly on medial
side so, ora serrata lies closer to limbus on
medial side
Its landmark externally is insertion of
medial rectus in medially and lateral recuts
in laterally

5. Inner layer of neuroectodermal cells
Differentiation of cells begins within
1month producing 3-4 compat cells
At 7th week, Nuclei segregate in outer 2/3rd
of primodial retina = outer primitive zone
Nuclei absent in inner 1/3rd = inner
marginal zone

6. Differentition of neuroepthelialcells begins
from center to periphery
2 layers:- a) inner neuroblastic layer
Ganglion cells, muller cells, amacrine cells
b) outer neuroblastic layer
Rods, cones, bipolar cells, horizontal cells
Separated by tangled cell processes =
transient nerve fiber layer of Chievtz
(inner plexiform layer)

7.  Starts around 6 weeks
 Origin= Pseudostratified columnar epithelial
cells of outer wall of cup
 Adjacent cells are joined by zonulae
occludentes and zonulae adherentes
 6th week = melanogenesis begins
 Differentiation starts from posterior to anterior
& by 8th week = single layer of hexagonal
columnar cells
 After birth = enlargement and expansion of
individual cells

8. As retina matures from center to periphery,
disproportiante amount of expansion
occurs in periphery,
hence, ganglion cell = lower density

9.  Pale-pink, well defined circular, 1.5mm in
diameter
 Comparatively pale due to: absence of
vascular choroid and lamina cribosa with medullated
nerve fibers behind it.
 No rods and cones (insensitive to light)–blind spot
 Centrally – depression = physiological cup: =
a)centre retinal vessels
b)varies in size, shape, position, depth
Sometimes, disc is more pink, scarcely any cup, seen
when central retinal vessels divide before they come
to surface

10. Optic disc unlike surrounding retina
doesnot have cells of muller; these cells
hold nerve fiber together hence optic disc
easily swells up in papilloedema.
Sometimes retina doesn’t reach edge of
disc leaving crescent of pigmented choriod
visible on ophthalmoscope

11. 5.5mm
0.35mm
1.5mm
150micm

13.  location- posterior fundus, temporal to optic
disc, between temporal vascular arcade
 Corresponds to 15 degree of visual field
 Functions :- photopic vision and color vision
 Yellow color in cadaver eye :- carotenoid
pigment ( zeaxanthin and lutein) in ganglion
and bipolar cells
 L:Z ratio: central area – 1:2.4
peripheral – 2:1
corresponds to rods:cone ratio
Lutein more in rods

14. Clivus 22

15. Thickness – 0.13mm
4mm temporal, 0.8mm inferior to optic disc
Photoreceptor layers made up of cones
Area of highest VA
Center of foveola is umbo
Correspond 1 degree of Visual field

16. Color of fovea persist and even
accentuated = called as cherry red spot
when surrounding retina become cloudy
due to ischemia eg CRAO and in
metabolic Storage disease

17.  Located inside fovea and outside foveola
 Important landmark in treatment of
subretinal neovascular membrane by
laser photocoagulation
 Parafovea = 0.5mm in width surrounds
fovea
GCL, INL, OPL are thickest
 Perifovea = 1.5mm

18. Retina around equator = equatorial retina
Divided into 4 regions:
1. Near periphery: 1.5mm around area
centralis
2. Mid periphery: 3mm around near
periphery
3. Far periphery: extend from equator to ora
serrata
4. Ora Serrata: area of retina and pars plana

19.  Peripheral margin of retina which consists of
dentate fringe (denotes termination of retina)
 Ora is 2.1 mm temporally and 0.7-0.8mm
wide nasally
 Watershed zone between anterior and posterior
vascular system hence retinal degeneration is
relatively common at periphery

20. Photoreceptors are malformed and
overlying retina frequently appears
cystic in parafin section

22. Monolayer of hexagonal cells containing
pigments merges with pigmented
epithelium of ciliary body
Unequal pigmentation of cells leads
granular appearance of fundus
Firmly attached to bruch membrane
Loosely attached to photoreceptor (between
= Subretinal space)
RD = separation between RPE and sensory
retina

24. 1. Vitamin A metabolism
2. Maintenance of outer retina-blood barrier
3. Phagocytosis of photoreceptor outer
segments
4. Absorption of light
5. Heat exchange
6. Formation of basal lamina
7. Active transport of material in and out of RPE
8. Production of mucopolysachharide matrix
surrounding outer segment

25. Apices of RPE has multiple villous process
that engage with photoreceptor outer
segments embedded in
mucopolysaccharide matrix (chondroitin-6-
sulfate, sialic acid, hyaluronic acid)
Lack of laminin and
Fibronectin in matrix,
Junctional complex between
Microvilli (prone for RD)

26. Contiguous RPE cells are firmly attached
By junctional complex.
Zonulae occludentes and adherentes
provide structural stability and maintain
outer retinal barrier
Number – 4.2 to 6.1 million
RPE cells in fovea are taller and thinner
and contain more and larger melanosome
Hence decreased transmission of choroidal
fluorescence during FFA

27.  contains multiple round and ovoid pigment
granules :- 1)melanosomes (apex)
This melanin absorb stray light and
minimize scatter
2) Lipofuscin granules :- arise from outer
segment of photoreceptor, represent
residual bodies from phagosomal activity
Aka wear and tear pigment

28. 3) Phagosome = membrane enclosed
packets of disc outer segments engulfed
by RPE
4) Mitochondria = aerobic metabolism
5) RER
6) Golgi apparatus

29. Incompletely digested residual bodies,
lipofusin, phagosome = drusen
Located between basement membrane of
RPE cells and inner collagenous zone of
bruch membrane
in ocular albinism-loss of melanin in RPE
and uvea. O/E once can see through
iris(transillumination of iris) and visualize
ciliary process and pupil is red
In older age, melanin combine with
lysosome – breakdown – hence, fundus
appears less pigmented.

30. PDGF- cell growth and healing
VEGF- stimulate normal or pathologic
neovascular growth
TGF- moderates inflammation
PEDF- neuroprotectant

31. Composed of
neuronal,
glial
vascular elements

32. Photoreceptor layer - Rods and cones
Average 92 million rods and 4.6 million
cones
Consist- outer and inner segment
Outer segments, surrounded by
mucopolysaccharide matrix and make
contact with RPE

33. Highest density of cones is at fovea
Number of cones falls off rapidly outside
fovea
Cones are greater on nasal and inferior
Rods are absent at fovea but present in
large number in ring-shaped zone 5-6mm
from fovea

36.  Rod outersegment – cylindrical, multiple laminated
disc (600-1000) resembling stack of coin and cilium
(connects outer and inner segments)
 Microtubules of cilium have 9 plus 0 cross-sectional
configuration (nonmotile)
 Inner segment – a) outer eosinopilic ellipsoid –
mitochondria
b) inner basophilic myoid-
glycogen and ribosome (protein synthesis)
 Inner portion of cell consist of spherule formed by
single invagination accommodating 2 horizontal cell
process and 1 or more central bipolar process

38. Outer segments have different morphology
depending on location on retina
Extrafoveal cone have short conical
ellipsoids and myoids and nucleus tends to
be closer to ELM
Foveal cone have longer cylindrical inner
segments
Cones outersegment have more disc (1000-
1200) & attached to each other
Intradisc and interdisc space are wider

40. Cone inner segments: at fovea are long
and tapered but at periphery are conical
Ellipsoid part - more mitochondria (200-
300 per cells)
Unlike rod inner segment is directly
continuous with its nucleus
Cone pedicle synapse with other rods,
cones, horizontal and bipolar cells
process.

42. 3 classes of cones: red, green, blue
(sensitive at 560, 530 and 430nm)
Gene for cone is in X chromosome.
Color blindess more common in males

43. Bipolar cells are oriented vertically, axons
synapse with rods and cones forming outer
plexiform layer and with axons of
ganglionc cells and amacrine cell forming
inner plexiform layer
Form 1st order neuron

44. Rod- connect rod to ganglion cell
Flat- many cones with many ganglion
Midget- single cone with single ganglion

45.  Axons of ganglion cells bend to become
parallel to retina forming nerve fiber layer.
 Ganglion cell forms second order
neuron(nerve cells of LGB -3rd order)
 Nerve fiber from temporal retina follow
arcuate around macula entering sup and inf
pole of optic disc
 Visibility of nerve fiber is enhanced using
green illumination

46. Unna orcein polychrome stain
a) rods- colourless
b) cones- deep blue
Mallory trichome stain and fixation with
zenker fluid
a) rods – blue
b) cones – red
In foveola all photorecepter stain red,
indicates- absence of rods

47.  Muller cells – extend vertically from ELM to
ILM
 Nuclei located in INL
Fx :- a)structural support, nutrition to retina
b)insulin and GF produced by muller
cells helps in metabolism of sensory retina
c) degradation of glutamate and GABA
d)mRNA for CA II – buffering CO2
liberated into extracellular space by
neurosensory retina
 Contains :- retinaldehyde binding protein,
glutamine, taurine

48. Astrocytes
Microglia
Oligodendrocytes

49. Outer 4 layers- choriocapillaris
Inner 6 layers – central retinal artery
Outer plexiform layer supplied by both
Macula - superior and inferior temporal
branches of central retinal artery
30% - cilioretinal artery, branch of ciliary
circulation supplies inner retina
Retinal vessels are end arteries but
anastomosis occur bet retinal and ciliary
system with vessel which enter Optic nerve
head from arterial circle of zinn.

50. Retinal blood vessels forms Blood-retina
barrier fromed by
single layer of nonfenestrated
endothelial cells with tight junction
(presence of barrier is confirmed by absence
of fluorescein leak from capillary)
Basal lamina covers outer surface of
endothelium.
Contains an interrupted layer of pericytes (
mural cells)

51.  Pericytes are also surrounded by a layer of
basement membrane.
 Pericytes contain contactile protein so contract
in response to angiotensin and relax to CO2
and nitric oxide
 Young:- endothelial cell : pericytes = 1:1
 In DM relative decrease in pericytes
 With inc age gradual decrease in endothelial
cells
 Retinal blood vessels lack internal elastic
lamina and smooth muscle cell
 When venules and arterioles cross they share
common basement membrane. Hence venous
occlusive disorder are common at AV crossing

53. First branch of ophthalmic artery
Arises near optic foramen and course as
follows:
Outside optic nerve: runs a wavy course
forward below optic nerve, inferomedial
aspect of nerve it bends upwards to pierce
dura and arachnoid.
In subarachnoid space: it bends upwards
and invaginates pia reaching centre of
nerve (surrounded by sympathetic nerve-
nerve of Tiedemann)

54. In centre of optic nerve: bends forwards
and with vein lie in temporal side, pierces
lamina cribosa and appear in eye
In optic nerve head: lies superficial nasal
of cup and divides into 2 branches superior
and inferior which subdivides into temporal
and nasal branch near margin

55. In retina: 4 branches superior nasal,
superior temporal, inferior nasal, inferior
temporal divide dichotomously and
proceed towards ora serrata

56. Accompanies retinal artery
Diameter 1/3rd larger than artery
Artery tends to lie superficial to vein thus
tend to cross superficial to the vein
Drains to cavernous sinus or superior
ophthalmic vein

57. 1. ELM- outermost layer, not a true
membrane, formed by attachment sites of
adjacent photoreceptors and muller cells,
highly fenestrated
2. ONL- nuclei of cones and rods
(cones>rods).
Nasal to disc: 8-9 layers of nuclei
Temporal to disc: 4 rows
Fovea: 10 rows
Rest of retina except ora: 1 cone nucleiand 4
rods

58. 3. OPL-synapse between rod
spherules,cone pedicles with dendrite of
bipolar and horizontal cells. Thickest at
macula and contains more fibers and more
oblique as they deviate from fovea (henle
fiber layer)
4. INL- nuclei of Bipolar, muller, horizontal,
amacrine cells

59. 5. IPL- axons of bipolar and amacrine cells
and dendrites of ganglion cells
absent at foveola
6.GCL- cell bodies of ganglion cells
Single row except at macula 6-8 layered
In glaucoma, defect is in GCL, Inc IOP leads to
anoxia, reduced axonal transport and excess
glutamate (excitatory damage)- apoptosis of
GCL
7. NFL- formed of axons of ganglion cells,
unmyelinated, 0.5-2micm, converge at optic
nerve head, pass through lamina cribrosa.
It also contains: Centrifugal nerve fiber
Muller processes, Neuroglial cells

61. In some case ganglion nerve fiber sheath
are myelinated usually seen around optic
disc; such area are nonseeing and
produce a blind spot
Arterial branch run in NFL close to ILM.
ILM is extremely thin and transparent,
hence retinal blood vessels are easily seen
in ophthaloscope

62. SR
F
IRF
Superior Arcuate fiber
Inferior arcuate fiber
thinnestthickest

63. Papilloedema: first appear in nasal fibers
Rise in CSF pressure in meningeal sheath
that surrounds optic nerve impedes axon
flow and cause disc to bulge into eyeball
Arcuate nerve fibers – most sensitive to
glaucomatous changes
Macular fibers lateral quadrant most
resistant to glaucomatous damage.

64. ILM- formed by footplate of muller cells
and attachments to basal lamina.
Cells and process are oriented
perpendicular to RPE in middle and outer
layers but, parallel in inner layers.
Hence, deposits of blood or exudates tend
to form round blot in outer layers and flame
shaped in nerve fiber layer
At fovea,outer layer parallel to surface so
star shaped patterns arise when exudate
collects

65. Fundamentals and principles of
ophthalmology- AAO
Clinical anatomy of eye –snells
Wolf’s anatomy
Retina and vitreous- AAO section 12