Endogenous hyaluronan in corneal disease

Hyaluronan (HA) is a disaccharide polymer capable of binding considerable amounts of water. It is present in trace amounts on the cornea endothelium, and it is not normally found in the epithelium or stroma. A specific histochemical stain was used to test for HA in a wide variety of corneal disorders. METHODS. Eighty-six human corneal tissue specimens were examined histochemically for HA. The material consisted of 84 full-thickness corneal buttons, one epithelium scraping, and one pterygium. Cases were analyzed according to the patient's sex, age, diagnosis, and localization of HA staining.

The corneal tissue specimens came from 47 women and 39 men, average age 59 years. Fifty-seven percent of the specimens displayed abnormal HA. HA was visualized in Fuch's dystrophy, keratoconus, infections, regrafts, mechanical and chemical trauma, post-excimer ablations, dystrophies, degenerations, pseudophakic bullous keratopathy, congenital opacities, Stevens-Johnson syndrome, and others. Staining was variously seen in the epithelium, stroma, and endothelium, with intensity of staining ranging from trace amounts to extremely heavy.

Endogenous hyaluronan production is seen in virtually the entire spectrum of corneal disorders. The presence of HA was most often associated with dividing, migrating, or fibroblast-like cells and probably represents a nonspecific tissue response to wounding. Its production is biochemically distinct from that of normally present proteoglycans. The abnormal presence of HA may reduce corneal transparency by disrupting the normal spacing between collagen fibrils, creating focal changes in the index of refraction, and altering the normal flow of solutes through the cornea.