CORNEA GENERAL FEATURES
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Anatomy of Cornea
Anterior surface
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elliptical
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Posterior surface
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circular
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Corneal horizontal diameter of both surfaces in adult
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11.7mm
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Corneal vertical diameter of anterior surfaces in adult
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11.7mm
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Corneal vertical diameter of posterior surfaces in adult
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10.6mm
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Cornea diameter at birth
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10mm
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Cornea attains adult diameter
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2 years
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Thickness of cornea at centre
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0.5 – 0.6 mm
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Radius of curvature on anterior surface & posterior surface of cornea
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7.8 mm & 6.5 mm
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The vertical meridian of cornea is 0.05 steeper than the horizontal meridian
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Astigmatism with the rule
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Refractive power
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43-44 D(3/4th of total dioptric power of eye)
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Refractive index
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1.376
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Most of refraction in eye occur at
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Anterior surface of cornea(air-tear interface)
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Megalocornea
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The horizontal diameter is of adult size at birth or >/ 13 mm after the age of 2 years
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Megalocornea
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Marfan syndrome
Ehler danlos syndrome
Down syndrome
Apert syndrome
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Microcornea means diameter less than
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10 mm
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Microcornea
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Autosomal dominant associated with hypermetropia, associated with fetal alcohol syndrome
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Long collagen fibres with wide spacing between them
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Cornea
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Critical angle for cornea air interface
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46*
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Epithelium of cornea
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Stratified squamous non keratinizing
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Corneal epithelium
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Hydrophobic
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Bowman’s membrane
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Once destroyed,doesn’t regenerated
Not a true membrane,condensed superficial stroma
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Stroma (substantia propria)
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Occupies 90% of thickness
Consists of collagen fibres in hydrated matrix of proteoglycans
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Dua’s layer is between
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Corneal stroma and descemet membrane
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Termination of descemet membrane
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Ring of schwalbe
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Endothelium
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Single layer of flat polygonal cells
Cell density - around 3000 cells/mm2 in young adults
Metabolically active layer
Has active pump mechanism
Most important layer in maintaining transparency
Regeneration occurs rapidly after injury(decompensation occurs only after >75% cells are lost
Krukenberg spindle is seen
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Regeneration of corneal epithelial cells from
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Palisade of Vogt
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Corneal transparency is due to
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Homogeneity of refractive index throughout the epithelium
avascularity, Peculiar arrangement of lamellae,Uniform spacing of collagen fibrils in stroma
Unmyelinated nerve fibres
Relatively dehydrated state
Na+ K+ pump,Bicarbonate dependent ATPase,Na+/H+ pump
Normal IOT
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Ion pump in corneal endothelium is necessary for maintaining transparency. it can be blocked by
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Inhibition of anaerobic glycolysis
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Avascular coat in eye
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Cornea
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The most actively metabolizing layers of cornea
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Epithelium & Endothelium
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Cornea receives nutrition form
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Atmosphere, aqueous humour,perilimbal capillaries
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Corneal vascularization is associated with
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Riboflavin deficiency
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Corneal neovascularization is caused by
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Graft rejection, Chemical burn, Contact lens usage, Viral
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or fungal keratitis
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Corneal neovascularization can be prevented by
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Photocoagulation
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