The document discusses the histology of the normal corneal layers and pathology in endothelial decompensation. It describes the five layers of the cornea - epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium. The stroma makes up 90% of the corneal thickness and contains lamellae of collagen fibrils and keratocytes. Endothelial decompensation occurs when the endothelial pump fails, allowing stromal edema and clouding.

1. HISTOLOGY OF THE NORMAL
CORNEAL LAYERS AND PATHOLOGY
IN ENDOTHELIAL
DECOMPENSATION
Presenter:Dr.Mugabi Barnabas
Moderator:Dr.Otiti.

2. OUTLINE
 HISTOLOGY OF THE NORMAL CORNEAL LAYERS
 ENDOTHELIAL DECOMPENSATION
 RETROCORNEAL FIBROUS MEMBRANE.
 CORNEAL HEALING

3. INTRODUCTION
 The cornea is a clear avascular tissue consisting of 5 layers:
 Horizontal diameter 11.7 mm wide and in the vertical diameter 10.6 mm.
 The posterior surface of the cornea appears circular, about 11.7 mm in
diameter.
 The axial thickness of the cornea is 0.52 mm with a peripheral thickness of
0.67 mm.

6. INTRODUCTION
 At birth the cornea is slightly thicker than that in children, perhaps
reflecting the onset of endothelial function close to the time of birth.
 Its surface area is about 1.3cm2 and forms 1/6 of the surface area of the
globe.
 In its central third the optical zone the radius of curvature of the anterior
surface is about 7.7 mm and that of the posterior 6.9 mm in adults.
 The peripheral cornea is more flattened.

7. INTRODUCTION
 epithelium.
 Bowman layer.
 stroma
 Descemet membrane.
 Endothelium
 Dua’s layer

8. INTRODUCTION
 Functions:
 The main function of the cornea is refraction.
 Its forms the principal refractive surface and accounts for 70% (40-45
dioptres) of the total refractive power of the eye.
 Refractive requirements are met by the regular anterior curvature of the
cornea and the optically smooth quality of the overlying tear film.

9. INTRODUCTION
 The resistance of the cornea, which provides a protective layer and
contains the ocular pressure.It is due to the collagenous components of
the stroma.
 Most of the refraction of the eye occurs not in the lens but at the front
surface of the cornea at the tear/air interface.

11. Characteristics of the Central and
Peripheral Cornea
 The central cornea:
 Spherical
 Peripheral cornea:
 Flattens
 Contact lens fitting

12. Epithelium and Basal Lamina
 Its a lipophilic, nonkeratinized, stratified squamous epithelium
 It is continuous with that of conjunctiva but no goblet cells.
 The epithelium is 50-90 um thick.
 Consists of five or six layers of nucleated cells .

13. Epithelium and Basal Lamina
 The basal cells:
 The deepest layer.
 Arranged in a palisade-like manner well alignment on a basal lamina.
 They form the germinative layer
 These basal cells are columnar (10μm wide &15μm tall) with rounded
heads and flat bases.
 Each nucleus is oval and oriented parallel to the cell's long axis.

14. Epithelium and Basal Lamina
 The wing or umbrella cells:
 consists of polyhedral cells convex anteriorly which cap the basal cell and
send processes between them.
 Become wider and increasingly flattened towards the surface.
 The most superficial cells may be as wide as 50 μm and 4 μm depth retain
their nuclei and do not show keratinization.
 Their flattened nuclei project backwards

16. Ultrastructure of the epithelium
 The cells of the epithelium are joined with their neighbours with an
intervening space of no more than 20 nm.
 The basal cells join by desmosomes and to the underlying basal lamina by
hemidesmosomes.
 Both the wing and basal cells possess numerous tonofibrils about 8 nm in
diameter and basal cells filaments pass through the hemidesmosomal
structures to be inserted into the basal lamina.

18. Ultrastructure of the epithelium.
 The mode of attachment between superficial and deep epithelial cells.in
addition to the desmosomal connections.
 Tight junctions (zonulae occludentes) run circumferentially between
contiguous surface cells.
 Impermeable to small molecules like sodium ions which renders the
epithelium semipermeable in respect to the precorneal tear film.
 No restriction from stroma permiting epithelial oedema and widening of
the intercellular space incase the endothelial pump fails.

20. Ultrastructural Features Of The
Epithelium
 The most superficial cells of the epithelium have a hexagonal shape firmly
attach
 They exhibit surface microvilli or microplica, sometimes regarded as an
exaggeration of the plasma membrane infoldings.
 Microvilli are about 0.5mm high, 0.3 mm wide and 0.5 mm apart.
 It is likely that the microvilli serve a physical function in stabilizing the
deep precorneal tear film.
 Light and dark cells with varying density and type of microvilli present.
 It has been suggested that the dark cells are older and about to
desquamate.

22. Immune Cells Inside The Epithelium
 Langerhans cells which are antigen presenting cells that present the
antigen to the T lymphocytes.
 Present in fetal corneal but disappear in the mature corneal except in
peripheral epithelium.
 They are almost totally absent from the central cornea but will populate
this region in response to infection.

23. Ultrastructural Features Of The
Epithelium
Stem cells:
Epithelial cells are firmly attached to one another by desmosomes, they migrate
continuously from the basal region toward the tear film.
They also migrate centripetally from their stem cell source at the limbus.
Division of these cells gives rise to a progeny of daughter cells whose division
serves to maintain the corneal epithelium
Damage to limbal stem cells
Chronic epithelial surface defects.

24. Basal Lamina Of The Epithelium.
 Secreted by the basal cells, which also synthesize the hemidesmosomes
concerned in attachment of epithelium to the lamina.
 Irregular zone (0.51μm wide) of granuloamorphous and filamentary
materials.
 A deep osmiophilic lamina densa (30-60 nm) and a superficial lamina
Iucida (24 nm).
 It is thicker peripherally and is thickened in diabetes and certain corneal
disorders.
 It stains a deep pink with periodic acid-Schiff reagent.

25. Bowmans layer
 Modified region of the anterior stroma.
 Bowman's layer is a narrow, acellular homogeneous zone, 8-14 μm thick
just below the basal lamina of the cornea epithelium.
 It readily seperates from the endothelium under certain pathologies.
 The anterior surface is smooth and parallel to that of the cornea though
it’s infiltrated by the lamina densa and merges into the stroma behind.
 The perimeter of Bowman's layer, which has a rounded border, delineates
the anterior junction between cornea and limbus and is marked clinically
by summits of the marginal arcades of the limbal capillaries

26. Ultrastructural Features Of The
Bowman’s Layer.
 Bowman's layer consists of a felted meshwork of fine collagen fibrils of
uniform size, lying in a ground substance.
 Fibril diameter (24-27 nm) is less than that of substantia propria.
 Become progressively more orderly in their orientation posteriorly
blending and interweaving with the fibrils of the anterior stroma.
 Bundles of the stromal lamella insert into the Bowman's layer.

27. Ultrastructural Features Of The
Bowman’s Layer.
 The compacted arrangement of the collagen confers great strength to this
zone.
 Once destroyed it is not renewed but is replaced by coarse scar tissue.
 It is perforated in many places by unmyelinated nerves in transit to the
corneal epithelium.

28. Stroma (Substantia Propria).
 The stroma, about 500 μm thick, consists of regularly arranged lamellae of
collagen bundles 200-300 centrally and 500 μm in the periphery.
 These vary between 9-260 μm in width and 1.15-2 μm in height and lie in
a proteoglycan ground substance together with keratocytes.
 The lamellae are arranged in layers parallel with each other and with the
corneal surfaces.
 From limbus to limbus although this arrangement is less precise in the
anterior third of the stroma and still under study.

29. Stroma (Substantia Propria).
 In the deeper stroma the lamellae form strap-like ribbons which run
approximately at right-angles to those in consecutive layers.
 At the limbus, the bundles appeared to take a circular course. This
anatomy may influence the different effects of corneal or limbal incision
during cataract surgery on postoperative corneal shape.

30. Ultrastructural Features Of The
Stroma.
 Fibrils show the typical 64-nm periodicity of connective tissue collagens
with a micro period of 6 nm.
 The alternating bands of varying electron density within the 64-nm .
 There is a unique uniformity of fibril diameter: although there is a slight
increase in fibril diameter passing from the front to the back of the cornea
(27 nm opposed to 35 nm), there is no general agreement.
 Each stromal lamella comprises a band of collagen fibrils arranged in
parallel.

31. Ultrastructural Features Of The Stroma.
 Keratocytes:
 Occupy 2.5-5%.
 Synthesize stromal collagen and proteoglycan during development and
maintaining it thereafter.
 In transverse sections of the cornea they appear as long, thin, flattened
cells (maximally 2 μm thick) running parallel to the corneal surface.
 Occupy the entire cornea and they’re found predominantly between
lamellae occasionally within lamellae.
 Anteroposterior connections between keratocytes in adjacent planes do
not occur.

32. Ultrastructural Features Of The Stroma.
 Long flattened nuclei and while their sparse cytoplasm contains a full
complement of organelles, they are few in number.
 In normal cornea there is a limited rough endoplasmic reticulum but it
becomes extensively developed in activated keratocytes of injured or
inflamed cornea .

33. STROMA
 Less compacted posteriorly
 Intrastromal ring segments for keratoconus.

35. Stroma
 Lamellae:
• 200
• Narrow,small,auniform diameter
• Lattice arrangement of the collagen fibrils.
• Regular seperation
Transparency of the cornea

36. Stroma
 In stromal corneal oedema, increased separation of collagen fibrils is due
to formation of 'fluid lakes’ leading to the formation
Stromal clouding.
 Type 1 is the most abundant
 There are aswell types V, VI, VII, XII, and XIV.
 Type 111 associated with wound healing
 ', and results in stromal clouding.

37. Stroma
 90% of the total corneal thickness.
 keratocytes.
 ground substance.
 Collagen fibrils:
• Obliquely oriented lamellae.
• Perpendicularly oriented lamellae

39. Stroma
 Keratocytes:
 Both collagen and proteoglycans.
 2.4 million
 The density
 Active cells
 Flat profile and even distribution in the coronal plane

41. Immune Cells Of The Stroma.
 There are three types of immune cells that occasionally occur in normal
corneal stroma:
• Lymphocytes
• Macrophages
• Polymorphonuclear leucocytes (very rarely)

42. Descemet’s membrane
 Basement membrane.
 First appears at the second month of gestation.
 Thickness increases with age:
• It’s only 3-4 μm thick at birth,5μm thick in childhood and reaches a
thickness of 10-12 μm in the adult reflecting a difference between it foetal
and postnatal components.

43. Descemet’s membrane.
 Banded zone:
 Synthetic function of the endothelium.
 Rich in type IV collagen.
 Descemet's membrane is a strong resistant sheet closely applied to the
back of the corneal stroma, from which unlike Bowman's layer it is sharply
defined and the plane of separation is used at lamellar keratoplasty.

45. Descemet’s membrane.
 Descemet's membrane thickens with age and in degenerative conditions
of the corneal epithelium such as congenital endothelial dystrophy or
posterior polymorphous dystrophy.
 Its glycoprotein and proteoglycan content are responsible for the brilliant
pink staining with periodic acid-Schiff reagent as is common with other
basal laminae.

47. Descemet’s membrane.
 Central excrescences(corneal guttae)
 Early stage loss of endothelial cells
 Microscopic mushroom caps
 Endothelial surface of the cornea

48. Descemet’s membrane.
 Peripheral excescences(Hassale-Henle):
 In the adults in normal health status
 Genetic inheritance

49. Endothelium
 Single layer.
 Hexagonal cells.
 Neuroectodermal origin.
 Mitosis of the endothelium is limited in humans:
• While mitosis may occur in young human endothelial cells, it is infrequent
in the adult and it appears that cornea is supplied with a relatively fixed
population of about 500 000 cells which are replaced in a limited way after
injury.
 These cells differentiate from cells that migrate from the limbal area at the
earliest developmental stage.

50. Endothelium
 There is great individual variation in cell counts and in the gradual
decrease in density and in shape.
 Endothelial density is about 6000 cells per mm2 at birth and falls by about
26% in the first year.
 A further 26% is lost over the next 11 years but the rate of loss slows and
possibly stabilizes around middle age especially in polymegathous
endothelium.
 At birth the cells are 10 11-m in height, but become extremely flat (3-5 11-
m) with age.
 The width of the adult cell is 18-20 11-m. The endothelial cell has an oval
nucleus located centrally and about 7 11-m in width.

52. Endothelium
 The size, shape, and distribution of the endothelial cells.
 Active transport.
Stromal deturgescence.

53. Dua’s layer:
 According to a 2013 paper by Harminder Singh Dua's group at
the University of Nottingham, is a layer of the cornea that had not been
detected previously.
 It is hypothetically 15 micrometres (0.59 mils) thick, its located between
the corneal stroma and Descemet's membrane.
 ‘’Big bubble technique’’.
 Improves outcomes of patients undergoing corneal grafts and transplants.

54. Dua’s layer:
 Despite its thinness, the layer is very strong and impervious to air.
 While people like Prof.Mark Terry applauded the discovery,others like
McKee et al criticized the validity of the discovery.

55. Dua’s layer
 Corneal hydrops:
 Build up of fluids in the cornea that is common in patients with
keratoconus
 Cornical deformity

56. Dua’s layer
 Descemetocoele:
 Extreme focal thinning.
 Erosion by the corneal ulcer.

57. Degeneration of the endothelium.
 Physiology:
 Active cell pump
 It provides a barrier function to the ingress of salt and metabolites into the
stroma, which has a spontaneous tendency to take up water& salt by
osmosis.
 It actively reduces the osmotic pressure of the stroma by metabolically
pumping the bicarbonate ions out of the stroma and back into the
aqueous humour.

58. Endothelial decompensation
 Corneal oedema:
 Post-mitotic and divide rarely
 Trauma or insults
 Sliding and enlargement of the adjuscent endothelial cells
 Endothelial cell density
 Increase in cell size and cell shape variation

59. Degeneration of the endothelium.
 Corneal endothelium result in loss of endothelial cells, and because of the
poor reparative power of human endothelium the loss in continuity of the
endothelial sheet is made up by a sliding process in which neighbouring
cells move over to fill the gap.
 The process of sliding of cells and decreased endothelial cell density is a
normal ageing phenomenon, which accounts for the fall in endothelial
density which occurs with age.
 Adult human endothelial cells rarely undergo cell division spontaneously.

61. Endothelial decompensation
 Progressive loss of corneal endothelial cell function and density and results
in a number of corneal pathologies.

62. Endothelial decompensation.
 Light scatter:
 Disruption of the normally uniform periodic spacing of the Type 1 collagen
fibrils.
 Irregularity at the optically critical tear film-air interface.
 Degrade optical performance of the cornea and compromise visual
acuity.

63. RETRALCORNEAL FIBROUS
MEMBRANE
 Infiltration of polymorphonuclear leukocytes in response to severe corneal
injury can induce endothelial cells to become fibroblastic.
 Descemet membrane and the corneal endothelium.
 Decrease in visual acuity.

64. Causes of endothelial disease
 Endothelial trauma from intraocular surgery.
 Fuch’s dystrophy
 Irirtis(AAU)
 Aging
 Narrow-angle glaucoma

65. Stages of healing of the cornea.
 Immediate phase: retraction of Descemet’s membrane and stromal
collagen, anterior and posterior wound gaping of the wound, fibrin plug
formation from aqueous fibrinogen, and stromal edema.
 Leukocytic phase: at around 30 minutes, polymorphonuclear leukocytes
from the conjunctival vessels and from the aqueous invade the wound.
Limbal wounds have an invasion of mononuclear cells from limbal vessels.
These can transform to fibroblasts after 12–24 hours.

66. Stages of healing of the cornea.
 Epithelial phase: at 1 hour full thickness ingrowth is inhibited by healthy
endothelium.
 Fibroblastic phase: central corneal wound fibroblasts are derived from
keratocytes. They produce collagen and mucopolysaccharides to form an
avascular matrix.
 Endothelial phase: at 24 hours endothelial sliding allows for coverage of
the posterior wound.

67. REFERENCES

68. THANK YOU