Structural implications of small-angle light scattering from cornea

Small angle light scattering (SALS) patterns are recorded from the central region of rabbit and bovine corneas. These measurements differ from those of other investigators in that an applied transcorneal pressure maintains the cornea's curvature. The experiment shows, for the first time, that rabbit and bovine SALS have the same essential features and the same behavior with increasing pressure. We also fixed corneas under an applied transcorneal pressure for electron microscopy and confirmed that this treatment flattens the usually undulating lamellae. Thus, we explain the form of the SALS patterns and their behavior with pressure in terms of scattering from corrugated lamellae which become straight upon application of a differential hydrostatic pressure. The wavelength of the corrugations is approximately constant as their amplitude decreases and a small amount of waviness remains even at normal intraocular pressure. The experiments show that the collagen fibrils are optically anisotropic, with their polarizability at 45° with respect to the fibril axis. The results also suggest that the orientation directions of the corneal lamellae are not random; rather there are either: one preferred direction or two preferred directions which are orthogonal, although some lamellae are evidently oriented in every direction. The preferred directions are correlated with the overall corneal geometry and do not vary among different corneas.