Introduction Transparent,avascular,watch-glass like structure. Forms 1/6th part of outer fibrous coat (Sclera) It is the major refracting surface of the eye 3. Dimensions + Avg horizontal dia =11.75 mm (ant surface) + Avg vertical dia = 11 mm (ant surface ) + Avg dia (post surface)= 11.5 mm + Thickness(centre) =0.52mm + Thickness(peripheral) = 0.67mm + Radius of curvature (ant surface) = 7.8mm + Radius of curvature (post surface)= 6.5mm + Refractive power (ant surface) = +48D + Refractive power(post surface)= - 5D + R.I = 1.376 4. Histology + Epithelium + Bowman’s membrane + Stroma + Dua’s layer + Descemet’s membrane + Endothelium 5. Epithelium + Made up of stratified squamous epithelium + Thickness - 50-90 um + 5-6 layers of cells + Regenerative, entire epithelial layer is replaced every 6-8 days + Made up of 3 types of cells - basal,wing, flattened cells + Cells are attached by to each other by means of desmosomes & maculi occludents 6. Bowman’s membrane + Acellular,Non regenerative + Made up of condensed collagen fibrils. + Thickness - 12um + Resistant to infection & injury.

1. Cornea
Optom.Monika Pallan

3. Introduction
Transparent,avascular,watch-glass like structure.
Forms 1/6th part of outer fibrous coat (Sclera)
It is the major refracting surface of the eye

4. Dimensions
+ Avg horizontal dia =11.75 mm (ant surface)
+ Avg vertical dia = 11 mm (ant surface )
+ Avg dia (post surface)= 11.5 mm
+ Thickness(centre) =0.52mm
+ Thickness(peripheral) = 0.67mm
+ Radius of curvature (ant surface) = 7.8mm
+ Radius of curvature (post surface)= 6.5mm
+ Refractive power (ant surface) = +48D
+ Refractive power(post surface)= - 5D
+ R.I = 1.376

5. Histology
+ Epithelium
+ Bowman’s membrane
+ Stroma
+ Dua’s layer
+ Descemet’s membrane
+ Endothelium

6. Epithelium
+ Made up of stratified squamous epithelium
+ Thickness - 50-90 um
+ 5-6 layers of cells
+ Regenerative, entire epithelial layer is replaced every 6-8 days
+ Made up of 3 types of cells - basal,wing, flattened cells
+ Cells are attached by to each other by means of desmosomes & maculi
occludents

7. Bowman’s membrane
+ Acellular,Non regenerative
+ Made up of condensed collagen fibrils.
+ Thickness - 12um
+ Resistant to infection & injury.

8. Stroma
+ Thickness: 0.5mm (90% of corneal thickness)
+ Consists of collagen fibrils ( type I & type V fibrillae interwined with filaments
of type VI collagen ) embedded in hydrated matrix of proteoglycans
+ Lamallae are arranged in 200-250 layers
+ Oblique arrangement of lamallae - Ant. 1/3rd part of stroma
+ Right angle arrangement of lamallae - Post. 2/3rd part of stroma
+ Parallel arrangement of lamallae - periphery
+ Consists keratocytes, macrophages,histiocytes, leucocytes

9. Dua’s layer
+ It is present between stroma & descemet’s membrane
+ Tough, well - defined ,acellular layer
+ Thickness - 10 -15 um

10. Descemet’ membrane
+ Also known as posterior elastic lamallae
+ Regenerative,elastic,strong homogenous basement membrane of corneal
Endothelium , bounds stroma posteriorly.
+ Very resistant to chemical agents,trauma & pathological processes.
+ Made up of collagen & glycoproteins
+ Thickness - 3um (birth)
+ Thickness- 10-12 um (young adults)
+ Maintains integrity of eyeball for long, even in absence of stroma

11. Endothelium
+ Consists of single layer of hexagonal cells fitting like mosaic tiles.
+ Cell density - 3000 cells/mm sq in young adults,which decreases with
advancing age
+ It is involved in active secretion & energy production
+ Contains large number of mitochondria
+ In eye ,next to photoreceptors ,endothelial cells contain highest no of
mitochondria
+ The cells have ‘active pump ‘mechanism
+ Corneal decomposition occurs only after more than 75% cells of endothelium
are lost.

12. Blood supply
+ Cornea is avascular
+ Small loops derived from the anterior ciliary vessels invade its periphery for
about 1 mm.
+ Loops of vessels are present in the sub - conjunctival tissues.

13. Nerve supply
+ Anterior ciliary nerves (branch of opthalmic nerve )
+ After going 2 mm in cornea, the nerves lose their myelin sheath and divide
dichotomously & form 3 plexuses - stromal,sub epithelial & intraepithelial