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 .