At its centre, a human corneal stroma is composed of about 200 flattened lamellae (layers of collagen fibrils), superimposed one on another.

The lamellae are produced by keratocytes (corneal connective tissue cells), which occupy about 10% of the substantia propria.

Proteoglycan protein cores attach to the surface of the collagen fibrils with the GAG chains projecting outwards.

These bridges are subject to thermal motion which prevents them from assuming a fully extended conformation.

At the same time the charges on the GAG chains attract ions and water molecules by the Donnan effect.

A balance between attractive and repulsive forces is reached for specific inter-fibrillar distances, which depends on the type of proteoglycans present.