Changes in the X-ray diffraction pattern of porcine lens before and after simulated accommodation

Purpose During the accommodation process, the morphology of the lens changes. The crystallin proteins within the lens fibres are the primary structural unit of organisation at the cellular level, and play a major role in maintaining transparency and refractive power. All the structural information about the lens from X-ray scattering techniques have so far been performed on samples in the relaxed accommodated state. It is thought that largest structural changes occur in the lens nucleus during accommodation. Aims To measure any changes in the average distance between the crystallin proteins, and their ordering within the lens fibres before and after stretching using small angel x-ray scattering. Methods Fresh porcine lenses were mounted into a commercially available lens stretching device (Bioniko, Florida, USA). Samples were placed in the X-ray beam at the Diamond synchrotron and 2D grid scans performed. Scans were taken in the same lens in both the accommodated and unaccommodated states, before and after a stretching. Results All patterns show a reduction in both the X-ray intensity and in the average spacing between the crystallin proteins, in the centre of the lens compared with the periphery. This is consistent with the increase of protein concentration from the lens cortex to the nucleus. No significant changes in the average spacing between the crystallin proteins was observed upon stretching. Substantial changes in both the X-ray intensity, and in the ordering of the proteins were recorded at the peripheral margins of lenses in the stretched state. Conclusions The changes in the X-ray intensity, and in the ordering of the crystallin proteins at the peripheral margins of the lens are somewhat in contrast to the notion that the nucleus under goes the largest structural changes