Describe the main cycle in metabolism of cornea.

Main Cycle:

Glycolysis is represented by the central chain and involves the anaerobic conversion of glucose into pyruvic acid. Lower part of the cycle, the Kreb's Cycle (TCA cycle) is the aerobic utilisation of pyruvic acid for energy production. Left section represents the HMP (pentose shunt) which is a major substrate for protein synthesis.

In the process of the cycle providing the major part of the energy (Kreb's cycle) oxygen is required. The oxygen enters from atmosphere directly under open eye conditions when it is exposed to tear film PO, of 155 inm Hg. Thc pO₂, drops to 55 mm Hg in sleep. The cornea consumes about 3.5 ml/cm2/hr of oxygen. The corneal stroma is morphologically and physiologically divided into anterior and posterior lamellar stroma. It consists of bundles of collagen (type I and type V) fibres arranged as lamellae. In Bowman's layer, the interstices of the fibrils are filled with type VI collagen, proteogylcans, keratan sulphate, decorin and fibromodulin.

The elldothelium and epithelium are the most actively metabolizing of all layers.