STRUCTURE OF CORNEAL SCAR TISSUE - AN X-RAY-DIFFRACTION STUDY

Full-thickness corneal wounds (2 mm diameter) were produced in rabbits at the Schepens Eye Research Institute, Boston. These wounds were all owed to heal for periods ranging from 3 weeks to 21 months. The scar t issue was examined using low- and wide-angle x-ray diffraction from wh ich average values were calculated for 1) the center-to-center collage n fibril spacing, 2) the fibril diameter, 3) the collagen axial period icity D, and 4) the intermolecular spacing within the collagen fibrils . Selected samples were processed for transmission electron microscopy . The results showed that the average spacing between collagen fibrils within the healing tissue remained slightly elevated after 21 months and there was a small increase in the fibril diameter. The collagen D- periodicity was unchanged. There was a significant drop in the intermo lecular spacing in the scar tissues up to 6 weeks, but thereafter the spacing returned to normal. The first-order equatorial reflection in t he low-angle pattern was visible after 3 weeks and became sharper and more intense with time, suggesting that, as healing progressed, the nu mber of nearest neighbor fibrils increased and the distribution of nea rest neighbor spacings reduced. This corresponded to the fibrils becom ing more ordered although, even after 21 months, normal packing was no t achieved. Ultrastructural changes in collagen fibril density measure d from electron micrographs were consistent with the increased order o f fibril packing measured by x-ray diffraction. The results suggest th at collagen molecules have a normal axial and lateral arrangement with in the fibrils of scar tissue. The gradual reduction in the spread of interfibrillar spacings may be related to the progressive decrease in the right scattered from the tissue as the wound heals.