Proteoglycans and collagen fibre organization in human corneoscleral tissue

Many investigators have suggested that the acidic glycosaminoglycan component of proteoglycans may control the size and organization of collagen fibres. It was decided that the transition zone between central cornea and sclera is an ideal model for the study of the relationships between specific proteoglycans and the organization of collagen fibres. The number and size of collage fibres were correlated with the concentration and composition of acidic glycosaminoglycans at discrete intervals from mid-cornea to sclera. The concentration of acidic glycosaminoglycans is highest in the central cornea; keratan sulfate accounts for most of the acidic glycosaminoglycan and the remainder is chondroitin. The peripheral cornea has 24% less acidic glycosaminoglycan than central cornea. The proportion of keratan sulfate is decreased and chondroitin is replaced by chondroitin sulfate. Uniformity of fibre diameters and their arrangement decreases distally from the central cornea. The sharpest area of transition lies between the corneolimbus and the sclerolimbus where the rapid increase in fibre size and decrease in organization is accompanied by a rapid decrease in the concentration of acidic glycosaminoglycans (primarily a loss of keratan sulfate), and the presence of detectable quantities of dermatan sulfate. A direct relationship between degree of fibre organization and acidic glycosaminoglycan content was found. We conclude that the precisely ordered spacing of collagen fibres in the cornea is determined by specific molecular constraints imposed by the conformation of keratan sulfate proteoglycan. This study proviess further evidence that the organization of collagen fibres is controlled by proteoglycans.