ALTERED ORGANIZATION OF COLLAGEN IN THE APEX OF KERATOCONUS CORNEAS

Purpose: In 15 keratoconus corneas, the three-dimensional arrangement of collagen lamellae was investigated by means of scanning electron mi croscopy. Methods: Keratoconus corneas without visible scars were obta ined during perforating keratoplasty. The noncollagenous matrix of the stroma was removed with sodium hydroxide. Descemet's membrane was rem oved mechanically and deeper layers of the stroma were exposed by cutt ing the tissue tangentially to the corneal surface with an ultramicrot ome. The apical and the para-apical regions of keratoconus were compar ed to the central regions of normal corneas. Results: In the apical re gions of 1 l out of the 15 keratoconus corneas (73%), the arrangement of the collagen lamellae differs from those of the para-apical regions and normal corneas, Their collagen fibrils form uniform layers and no delimited collagen lamellae can be differentiated. Interlacing betwee n adjacent layers is extremely decreased or even absent. In the para-a pical region of keratoconus corneas the three-dimensional arrangement of collagen lamellae does not differ from that in normal corneas. Conc lusion: Stromal thinning and conical ectasia in the apex of keratoconu s corneas alters the organization of collagen. This will certainly aff ect the biomechanical properties of the cornea and further lead to a p rogression of keratoconus irrespective of its primary pathogenesis.