ENDOGENOUS HYALURONAN IN CORNEAL DISEASE

Purpose. Hyaluronan (HA) is a disaccharide polymer capable of binding considerable amounts of water. It is present in trace amounts on the c ornea endothelium, and it is not normally found in the epithelium or s troma. A specific histochemical stain was used to test for HA in a wid e variety of corneal disorders. Methods. Eighty-six human corneal tiss ue specimens were examined histochemically for HA. The material consis ted of 84 full-thickness corneal buttons, one epithelium scraping, and one pterygium. Cases were analyzed according to the patient's sex, ag e, diagnosis, and localization of HA staining. Results. The corneal ti ssue specimens came from 47 women and 39 men, average age 59 years. Fi fty-seven percent of the specimens displayed abnormal HA. HA was visua lized in Fuch's dystrophy, keratoconus, infections, regrafts, mechanic al and chemical trauma, post-excimer ablations, dystrophies, degenerat ions, pseudophakic bullous keratopathy, congenital opacities, Stevens- Johnson syndrome, and others. Staining was variously seen in the epith elium, stroma, and endothelium, with intensity of staining ranging fro m trace amounts to extremely heavy. Conclusion. Endogenous hyaluronan production is seen in virtually the entire spectrum of corneal disorde rs. The presence of HA was most often associated with dividing, migrat ing, or fibroblast-like cells and probably represents a nonspecific ti ssue response to wounding. Its production is biochemically distinct fr om that of normally present proteoglycans. The abnormal presence of HA may reduce corneal transparency by disrupting the normal spacing betw een collagen fibrils, creating focal changes in the index of refractio n, and altering the normal flow of solutes through the cornea.