Fig. 2.

Structural hierarchy in corneal collagen (not to scale). Three helical alpha chains are supercoiled to produce the collagen triple helix molecule (top right). These molecules self-assemble in a staggered axial array (bottom right) to form microfibrils consisting of five molecules which in turn coil together to form the 30 nm diameter collagen fibrils seen in the electron microscope. The micrograph bottom left is reproduced from Ottani et al. (2002), with permission of the copyright holder, and shows the coiled microfibrils within the collagen fibril; the micrograph bottom middle is reproduced from Baldock et al. (2002), with permission of the copyright holder, and shows the microfibrils in cross-section within the collagen fibril.