4. CORNEA
� Anterior 1/6th of fibrous coat
� Avascular
� Transparent structure
� Set into sclera like a watch glass
� Limbus: junction of cornea and sclera
5. DEVELOPMENT
� Epithelium: from surface ectoderm
� Other layers
� Endothelium, Descemet’s membrane, pre-
Descemet’s membrane, stroma & Bowman’s
layers: from fibrous layer of mesenchyme
lying anterior to optic cup
6. DIMENSIONS
Anterior surface Elliptical, 11.7 mm horizontal & 11mm
vertical diameter
Posterior surface Circular, 11.5 mm diameter
Thickness Average thickness is 540 micrometer &
measured with corneal pachometer
Radius of
curvature
•Central 5mm area: powerful refracting
surface of eye
Refractive index 1.376
Refractive power •45 dioptres (3/4th of total refractive power of
eye)
•Anterior surface:+48D (most important
refractive structure of eye) & posterior
surface:-5.80D
9. � LIMBUS EPITHELIUM
� Anterior cell wall of superficial cells has
microvilli which contain glycocalyx.
� Helps in adsorption of mucus layer of tear
film .
� Convert hydrophobic corneal surface
hydrophilic .
� Damage to this area – invasion of conjunctival
epithelium onto cornea.
10. BOWMAN’S MEMBRANE
� Acellular mass of condensed collagen fibrils.
12 micrometers in thickness.
� Shows considerable resistance to infection
� Once destroyed unable to regenerate
� Heals by scarring.
11. STROMA(SUBSTANTIA
PROPRIA)
� 0.5 mm thickness
� Constitute 90% corneal thickness
� Consists of collagen fibrils embedded in
hydrated matrix of proteoglycans
12. PRE-DESCEMET’S MEMBRANE
� Aka Dua’s layer
� Dr.Harminder Dua
� Anterior to Descemet’s membrane
� 15 micrometer thick
� Acellular
� Strong
� Impervious to air
13. DESCEMET’S MEMBRANE(POSTERIOR
ELASTIC LAMINA)
� Strong homogenous basement membrane of corneal
endothelium
� Resistant to chemical agents, trauma & pathological
processes
� Consist of collagen and glycoprotein
� Can regenerate
� Normal-state of tension
� When torn- it curls inwards on itself
� In periphery – appears to end at the anterior limit of
trabecular meshwork as Schwalbe’s line(ring)
14. ENDOTHELIUM
� Single layer of flat polygonal epithelial cells
� On slit-lamp biomicroscopy appear as mosaic
� Don’t proliferate in vivo
� Cell lose with age is compensated with
enlargement(polymegathism) and migration
of neighboring cells
� Cells contain ‘active-pump’ mechanism
� Keeps cornea dehydrated.
15. BLOOD SUPPLY
� Avascular structure
� Small loops derived from anterior ciliary
vessels invade its periphery for ~1mm
� In the subconjunctival tissue which overlaps
the cornea
16. NERVE SUPPLY
� Long ciliary nerves
� Branches of nasociliary nerve from
ophthalmic division of 5th cranial nerve
� Form 3 plexuses: stromal, subepithelial &
intraepithelial
18. CORNEAL EPITHELIUM
AND TEAR FILM.
Homogeneity of refractive
index throughout epithelium
PECULIAR
ARRANGEMENT of corneal
lamellae (lattice theory of
Maurice)
PECULIAR REGULAR
REFRACTIVE INDEX of
corneal lamellae with
variation <200 micrometer
(Goldmann and Benedek
theory)
AVASCULARITY of cornea
ANATOMICAL
FACTORS
19. PHYSIOLOGICAL FACTORS
� Keep cornea in a relative state of dehydration
(78% water content)
� BARRIER FUNCTION OF LIMITING
LAYERS (epithelium and endothelium)
� ENDOTHELIAL PUMPS. Most important
factor in maintaining corneal dehydration by
controlling fluid transport due to several
enzyme systems
20. � EVAPORATION from corneal surface
� NORMAL IOP
� SWELLING PRESSURE (SP) of stroma
which counters imbibition effect of IOP
� CORNEAL CRYSTALLINS. Water soluble
proteins of keratocytes contribute to corneal
transparency at cellular level
