This document provides an overview of the anatomy of the cornea including its dimensions, structures, physiology, and nerve supply. The cornea has 5 layers - epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium. It is avascular and transparent to allow for vision. The epithelium is stratified and squamous, the stroma contains collagen bundles, and the endothelium maintains deturgescence of the stroma. The cornea has important optical and protective functions for the eye.

1. ANATOMY OF CORNEA
Dr Nithin Keshav

2. Introduction
CORNEA – Medieval Latin “ co rne a te la “
HORNY WEB (latin ,cornu = horn)
 Transparent avascular tissue with a convex
anterior surface & concave posterior surface.
 Main function is OPTICAL
 Accounts for 70% of the total refractive power
of the eye (+ 43D)
 Other functions are: -STRUCTURAL
INTEGRITTY
-PROTECTION FOR

4. DIMENSIONS
 Anterior Surface :
Vertical – 11.7 mm
Horizontal – 10.6 mm
 Posterior Surface :
Both 11.7 mm
 Thickness :
Central 0.52 mm
Peripheral 0.67 mm
 Surface Area:
1.3 cm2

5.  Radius of Curvature
Anterior – 7.8 mm Central 1/3
Posterior – 6.5 mm
- Peripheral cornea is more flattened
 Topography
Anterior curvature is spherical in 2-4 mm zone
decentered upwards & outwards relative to
visual axis but centered to the pupillary
aperture( lies 0.4 mm temporally) --
CORNEAL CAPorAPEX
 Curvature varies from apex to limbus , greater

6. STRUCTURES
5 LAYERS
A nterior Epithelium
Bowman’s layer
C entral stroma
Descemets membrane
E ndothelium

8. EPITHELIUM
 Stratified , Squamous & Non Keratinized
 Continuous with conjunctiva , but no goblet
cells
 50-90 u
 5-6 layers
Posterior to anterior
1. BASAL CELLS
 Arranged in pallisade manner
 Germinative layer
 Columnar with an oval nucleus

9. 2. WING or UMBRELLA cells
 Polyhedral
 Convex anteriorly
3. SURFACE CELLS
 2-3 layers
 Polyhedral

10. Ultrastructural features
 Abundant mitochondria in wing & middle cell
layers
 High glycogen content (Wing & Superficial
layers)
 Tonofibrils ( Intermediate filaments)
 Desmosomes- lateral adhesion b/w cells,
mainly at the basal level.
 Zona Occludens- Tight jn seen at surface cells

11.  Tight jn are impermeable to Na ions & confer
semipermeable membrane properties to the
epithelium
 Surface cells contain MICROVILLI &
MICROPLICAE– Helps in stabilizing
precorneal tearfilm
 Dendritic cells ( langerhans cells )- present in
fetal epithelium but disappears in mature
cornea.

12. BASAL LAMINA
 2 LAYERS
 Superficial LAMINA LUCIDA
 Deep LAMINA DENSA
 Thicker peripherally
 Thickened in Diabetes , Corneal pathology, Old
age
 Integrated with the underlying Bowmans layer
through ANCHORING FILAMENTS &
ANCHORING PLAQUES
 Cohesion between Basal Lamina & Bowman’s
loosened by
 Lipid solvents


13. Physiology of Epithelium
 Rich in glycogen , serves as energy store in
aerobic conditions
Glycogen levels
 Hypoxia
Corneal sensitivity

14. Turn Over
 Limbal stem cells migrate towards centre
 XYZ Hypothesis :
Lim bal& Co rne albasale pithe lialce lls are
so urce fo r CO RNEAL EPITHELIAL CELLS
 TRANSIENT AMPLIFYING CELLS : Daughter cells of
limbal stem cells
 TRANSITIONAL CELLS: Basal cells lying between
limbus & peripheral cornea commonly seen at
Superior Cornea

15. Markers
 Epithelial cells – CK3
 Cells of regenerative regions (limbal, transient
amplifying cells & transitional cells)- CK19 ,
VIMENTIN
 Hemidesmosome – a6b4 integrin

16. Repair
 Mitosis inhibited by
1. Injury
2. Adrenergic agents
3. Surface anesthetics

17. 
Repair occurs by CENTRIPETAL SLIDE
Rearrangement of Actin fibrils
Amoeboid migration
Halted by CONTACT INHIBITION
Anchor
MITOSIS resumes until epithelial thickness is
re-established

18. TOTAL EPITHELIAL LOSS
Adjacent Conjunctival epithelium resurfaces
Cornea
Vascularised conjunctival type of epithelium
containing GOBLET CELLS

19. BOWMAN’S
 Aka Anterior Limiting Lamina
 8-14 u
 Modified region of anterior stroma
 Acellular homogenous zone
 Normally attached to Basal Lamina
 In pathological conditions
 Corneal edema , Dystrophy
 After death
-Epithelium readily seperates from this layer

20. Ultrastructural features
 Fine collagen fibrils of uniform size in ground
substance
 Relatively resistant to trauma (mechanical &
infective)
 Convex ridges can be seen when relaxed –
POLYGONAL /CHICKEN WIRE PATTERN
 Responsible for Anterior Corneal Mosaic
 In Pro lo ng e d Hypo to ny & Atro phic Bulbi
degenerative changes in the ridges contributes
to Secondary Anterior Crocodile Shagreen

21. STROMA
 500u
 Regularly arranged lamellae of collagen
bundles
 Contains keratocytes between lamellae
 Keratocytes – production of COLLAGEN &
PROTEOGLYCANS during development

22. Stromal repair
Keratocyte Activation
Migration
Transformation into Fibroblasts
 Requires presence of overlying epithelium

23. DESCEMET’S
 Aka Posterior Limiting Lamina
 2.2- 4.5 u
 It is Basal Lamina of Endothelium
 Appears at 2nd
month of gestation
 Strong resistant sheet
 Sharply defined & the plane of seperation is
used in LAMELLAR KERATOPLASTY
 Thickens with age , endothelial degenerations
 Type 4 collagen

24.  Anterior 1/3 :
 Oldest
 Irregular banded pattern in cross section
 Banding develops at 5th
month IUL
 POSTERIOR 2/3:
 Formed after birth
 Homogenous fibrillogranular material

25.  In Endothelial diseases where morphology &
thickness of Descemets is altered , presence
of no rm alante rio r bande d laye r can be used to
signify o nse t o f diso rde r afte r birth.
 In AGEING CORNEA:
 Bands of long spacing collagen found
 Focal overproduction of basal lamina like material
produces peripheralexceresences
HASSAL HENLE WARTS

27.  Physiological

Resemble Descemet’s warts of central
cornea – CORNEA GUTTATA in Fuch’s
 Peripheral rim of Descemets forms internal
landmark of corneal limbus & marks anterior
limit of angle – SCHWALBE’S LINE
 Prominent in 15-20% of individuals

28.  Hypertrophied in congenital anomalies –
POSTERIOREMBRYOTOXON
 On stripping Descemet’s it ROLLS INTO
STROMA
 Lens capsule curls outwards
 On injury endothelial cells resurfaces
& deposits Basal Lamina identical to
Descemets

30. ENDOTHELIUM
 Single layer of hexagonal / cuboidal cells
 Counts
 At birth : 6000/mm2
 1 yr : falls by 26%
 11yr : another 26%
 Gradual decrease in density & increase in
shape variation – POLYMEGATHISM

31. Ultrastructural features
 Lateral borders convoluted forming marked
interdigitation
 Cell junction
 Ant 2/3 : Maculae adherentes
 Post 1/3 : maculae occludentes
 Posterior surface shows Microvilli -
Absorptive surface area
 Abundant mitochondria
 Condensation of cytoplasm rich in actin lies
close to posterior membrane – TERMINAL
WEB

33. PHYSIOLOGY
1. NUTRITION :
 Glucose & aa
2. FLUID REGULATION:
 Maintains relative deturgescence by
1. Provides barrier to prevent ingress of salt &
metabolites into stroma
2. Decreases osmotic pressure of stroma by
active pumping out of bicarbonate.

34. 3. INJURY & REPAIR:
 Physical & chemical (ouabain)
 SLIDING PHENOMENA

35. STRUCTURAL PROTEINS OF
CORNEA
COLLAGEN
Basal lamina - type 4
Bowman’s - 5
Stroma - 1 (90%)
Descemets - 4

36. PROTEOGLYCANS
Keratan sulphate – 50%
Chondoritin sulphate
Chondroitin
 Peripheral cornea Dermatan sulphate &
Keratan sulphate

37. Stromal edema
 Altered biosynthesis of ground substance
 Dermatan sulphate present centrally
Scarring
 Keratan sulphate & Heparan sulphate and
Hyaluronate

38. CORNEAL TRANSPARENCY
 MAURICE THEORY:
LATTICE ARRANGEMENT of collagen
fibres is responsible for transparency.
 Due to small diameter & regular seperation of
collagen, back scattered light would be suppressed
by DESTRUCTIVE INTERFERENCE
 GOLDMAN THEORY :
If fibril seperation & diameter is less than 1/3 of
wavelength of incident light –TRANSPARENCY
ensues

39. Other factors
 Absence of blood vessels & pigments
 Absence of myelinated nerve fibres
 Uniform refractive index of all layers & uniform
spacing of collagen fibrils

40.  In ill fitting contact lenses & IOP, basal cells
which are regularly arranged are seperated by
edema fluid of differing refractive index to cells
DIFFRACTION GRATING EFFECT
HALOS AROUND LIGHT

41. NERVE SUPPLY
 Ophthalmic division of Trigeminal via Anterior
Ciliary Nerve
 Supply also from Cervical Sympathetic
 Anterior ciliary nerve enters sclera from
perichoroidal space just behind the limbus &
joins with the conjunctival nerve to form
PERICORNEAL PLEXUS

42.  Divides into 2 branches Anterior & Posterior
 Anterior passes subjacent to the BOWMANS
forming SUBEPITHELIAL PLEXUS
 Posterior innervates posterior stroma , does
not involve Descemets .