The primary function of the cornea is refraction. In order to perform this function, the cornea requires the following:
• smooth and regular surface
• spherical curvature of proper refractive power
• appropriate index of refraction.
Corneal transparency is contributed to by anatomical and physiological factors:
• absence of keratinisation of epithelium
• tight packing of epithelial cells
• mucous layer providing smooth lubricated surface
• homogeneity of membranes - Bowman's and Descemet's
• regular arrangement of corneal lamellae (parallel collagen fibres within each lamella, with adjacent lamellae being perpendicular). Regularity produces a diffraction grating
• paucity of corneal stromal cells, which are flattened within lamellae
• interspaces - absence of blood vessels.
• active dehydration of the cornea through Na+/HCO3- metabolic pump located in the corneal endothelium. This dehydration is supplemented by the physical barrier provided by the corneal epithelium and endothelium.
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