Vertical diameter (anterior surface) :10.6 - 11.7 mm
Horizontal diameter (anterior surface) : 11.6-12.6 mm
Avg. posterior surface diameter : 11.6-12 mm
Avg. corneal diameter at birth : 9.8 mm
Maximum increase in corneal diameter occurs during 6 to 12 months of age.
Megalocornea :
* Horizontal diameter >= 12 mm in newborns and >= 13 mm in adults.
* Horizontal diameter >= 12 mm in newborns and >= 13 mm in adults.
Microcornea :
* Horizontal diameter < 10 mm (down upto 4 mm)
* Horizontal diameter < 10 mm (down upto 4 mm)
Horizontal corneal diameter more than 12mm in the first year of life is highly suspicious for congenital glaucoma.
Refractive power of anterior central cornea : 48-48.8 D.
Approx. refractive power of central posterior corneal surface : -5.8 D.
Net corneal refractive power : 43 D (70% of total refractive power of eye).
Refractive power of a full term new born cornea : 51D.
Minimum 13% oxygen is required at the anterior corneal surface for normal corneal metabolism and to prevent lactate accumulation in aqueous.
Thickness of cornea : * periphery : 0.65-1mm
* centre : 0.47 - 0.62 mm
(0.5mm).
* epithelium : 50 - 100 microns.
* bowman's membrane : 8-13 microns.
* stroma forms 90% of total corneal thickness.
* thickness of descemet's membrane: 2-3 microns at birth. 20-30 microns in old age.
* centre : 0.47 - 0.62 mm
(0.5mm).
* epithelium : 50 - 100 microns.
* bowman's membrane : 8-13 microns.
* stroma forms 90% of total corneal thickness.
* thickness of descemet's membrane: 2-3 microns at birth. 20-30 microns in old age.
Avg. life cycle of a new epithelial cell is 3-7 days.
Corneal endothelial cell density:
* Highest at birth - 4000 cells/sq mm.
* 5 yrs of age- 3600+/- 400 cells/sq mm .
* adult - 2000 cells/sq mm.
* Highest at birth - 4000 cells/sq mm.
* 5 yrs of age- 3600+/- 400 cells/sq mm .
* adult - 2000 cells/sq mm.
After 2 years of age endothelial cell loss occurs at the rate of 0.56% approx. per annum.
Critical cell density to prevent corneal decompensation is 300-400 cells / sq mm.
Desirable endothelial cell density in donor tissue is atleast 2000 cells / sq mm.
Grading of corneal haze :
0 - clear cornea.
0.5- barely detectable or trace haze.
1 - mild haze not interfering with refraction.
2 - moderate haze interfering with refraction.
3 - marked haze that obscure iris details.
4 - severe haze that preclude iris details.
0 - clear cornea.
0.5- barely detectable or trace haze.
1 - mild haze not interfering with refraction.
2 - moderate haze interfering with refraction.
3 - marked haze that obscure iris details.
4 - severe haze that preclude iris details.
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