corneal physiology

The two primary physiological functions of the cornea are (i) to act as a major refracting medium; and (ii) to protect the intraocular contents. Cornea fulfills these duties by maintaining its transparency and replacement of its tissues.

Corneal transparency
The transparency is the result of :

• Peculiar arrangement of corneal lamellae (lattice theory of Maurice),
• Avascularity, and
• Relative state of dehydration, which is maintained by barrier effects of epithelium and endothelium and the active bicarbonate pump of the endothelium.For these processes, cornea needs some energy.

Source of nutrients
1. Solutes (glucose and others) enter the cornea by either simple diffusion or active transport through aqueous humour and by diffusion from the perilimbal capillaries

2. Oxygen is derived directly from air through the tear film. This is an active process undertaken by the epithelium.

Metabolism of cornea
The most actively metabolising layers of the cornea are epithelium and endothelium, the former being 10 times thicker than the latter requires a proportionately larger supply of metabolic substrates. Like other tissues, the epithelium can metabolize glucose both
aerobically and anaerobically into carbon dioxide and water and lactic acid, respectively. Thus, under anaerobic conditions lactic acid accumulates in the cornea.