The Cornea

The primary function of the cornea is refraction. In order to perform this function, the cornea requires the following:

• transparency

• smooth and regular surface

• spherical curvature of proper refractive power

• appropriate index of refraction.

Corneal transparency is contributed to by anatomical and physiological factors:

1. Anatomical:

• 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.

2. Physiological

• 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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