What light scattering can tell about the ordering of collagen fibrils in corneal stroma

Normal cornea transmits greater than 90% of visible light, but its transmission would be less than 30% if the stroma's collagen fibrils scattered independently of one another. Thus modern transparency theories are based on there being sufficient order in fibril positions for destructive interference to cause cancellation among the scattered fields. Two types of structure have been proposed: long-range crystalline order as used in the earliest theory, and short-range liquid-like order such as that depicted by electron microscopy. Of course structures depicted in electron micrographs may be distorted and other tests are required to determine the nature of the order. Light scattering measurements can afford such a test. Specifically, the two types of order produce different dependencies on wavelength for the scattering cross-section (angular or total) in the long-wavelength limit. Measurements must be analyzed appropriately to obtain the long-wavelength limit. The results reported in this paper demonstrate that measurements of both angular and total scattering cross-sections support short-range order of fibril positions.