De. Freund et al., ULTRASTRUCTURE IN ANTERIOR AND POSTERIOR STROMA OF PERFUSED HUMAN ANDRABBIT CORNEAS - RELATION TO TRANSPARENCY, Investigative ophthalmology & visual science, 36(8), 1995, pp. 1508-1523
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.