ULTRASTRUCTURE IN ANTERIOR AND POSTERIOR STROMA OF PERFUSED HUMAN ANDRABBIT CORNEAS - RELATION TO TRANSPARENCY

Purpose. The authors sought to discover whether there are differences in the degree of spatial order in the fibrillar ultrastructure between anterior and posterior stroma. Methods. Human corneas were obtained f rom eye bank eyes. Although they had been classified as normal, some s welling remained after 3 hours of deturgescence. Freshly excised, unsw ollen rabbit corneas also were used. Image analysis methods were appli ed to transmission electron micrographs of the anterior, middle, and p osterior stroma of these corneas to determine the positions and radii of fibrils, the fraction of total area occupied by fibrils, and the fi bril number density. Results were used to calculate the interference f actor that appears in the direct summation of the fields for light sca ttering theory and to estimate the total scattering cross-section per fibril. The interference factor is a measure of the spatial order in t he positions and sizes of the fibrils. Results. Electron micrographs s howed anterior-posterior variations in size and number density of fibr ils. The interference factor at wavelengths of visible light was lower in posterior stroma than in anterior stroma for humans and rabbits. I n some instances in humans, the anterior interference factor was chara cteristic of mildly swollen cornea. When averaged for the electron mic rographs analyzed, the anterior stroma was predicted to scatter approx imately twice as much light per unit depth as the posterior stroma in humans (at any given wavelength) and approximately three times as much in rabbits. Conclusions. Calculations of the interference factor show ed that there were differences in the anterior-posterior spatial order ing of fibrils. In human corneas, the differences could have been caus ed by intrinsic in vivo differences between anterior and posterior str oma; however, possible anterior-posterior variations in swelling betwe en the two regions in vitro also could have affected the results.