HUMAN CORNEA AND SCLERA STUDIED BY ATOMIC-FORCE MICROSCOPY

The purpose of this study was to investigate the ultrastructure of the extracellular matrix of human cornea and sclera by using the atomic f orce microscope (AFM). Specimens of human cornea (n=16) and sclera (n= 10) were obtained from a cornea bank or from enucleated eyes (n=1; cli nical and histopathological diagnosis: choroidal melanoma) and fixed i n Karnovsky solution. The AFM resolved individual collagen fibrils in corneal and scleral tissue. Scleral collagen fibrils had a diameter ra nging from 118.3 to 1268.0 nm and showed clear banding with a mean axi al D-periodicity of 77.02 nm. The mean gap depth between the two overl aps was larger in the sclera than in the cornea. The diameter of corne al collagen fibrils ranged from 48.0 to 113.0 nm. In contrast to the s clera, the corneal collagen fibrils did not exhibit clear banding as t heir surface pattern. Closely attached fibrils with a beaded to globul ar structure were predominant in the cornea. The mean axial D-periodic ity of the corneal collagen fibrils was 68.50 nm. In both tissues, the AFM resolved structures resembling cross-bridges between adjacent fib rils, The corneal collagen fibrils showed fibrillar properties that we re different from those of the sclera, and that therefore might be ess ential for the spatial organization responsible for the optical qualit y of the cornea.