THE IMMUNOHISTOCHEMICAL COMPOSITION OF CORNEAL BASEMENT-MEMBRANE IN KERATOCONUS

Purpose. Keratoconus is a gradually progressing disease of unknown cau se, characterized by central thinning, increased curvature, and finall y scarring of the cornea. This causes myopia and astigmatism and the u ltimate treatment is keratoplasty. We studied the composition of basem ent membranes (BMs) in normal, scarred and keratoconus corneas to find out possible changes specific for keratoconus. Methods. Frozen sectio ns of normal, scarred and keratoconus corneas were immunostained with various antibodies against basement membrane (BM) proteins and integri n beta 4. Results. In the keratoconus corneas, we found discontinuitie s or defects in Bowman's layer, sometimes distorted stroma beneath the defects, and also thinning of the stroma. The results show that withi n the defects in keratoconus corneas, there is an expression of protei ns that are not normally present in the corneal BM, i.e. collagen alph a(1/2) (IV) chains, and on the contrary, absence of the expression of some proteins, i.e. collagen alpha(5-6) (IV) chains that normally are continuously expressed in the corneal epithelial BM. In addition, eith er increased or decreased expression of laminin-l (alpha 1 beta 1 gamm a 1), laminin-5 (alpha 3 beta 3 gamma 2) and collagen type VII, depend ing on the keratoconus defect, was seen and the expression of integrin beta 4 was decreased. These findings seem to be specific for keratoco nus, as they were not found in scarred corneas. Conclusions. The resul ts show that the defects in BM and changes in the BM composition are i nvolved in the pathogenesis of keratoconus. Furthermore, it seems that scarring alone does not explain the breaks in Bowman's layer and immu no-histochemical changes seen in keratoconus. Therefore, we suggest th at a profess similar to wound healing, which is initiated by breaks in Bowman's layer, would largely contribute to the differences seen in k eratoconus corneas.