Morphological and biochemical analysis of intact and opaque cornea in dogs

The arrangement of collagen fibrils and glycosaminoglycans (GAGs) in substantia propria are important for maintaining transparency of the cornea. Interferences in collagen fibrils and GAG production could be adversative to corneal integrity. In this study, six dogs consisting of four Beagles with normal cornea (normal), one Beagles with opaque cornea (sample No. 1) and one Shih Tzu with neovascularization opaque cornea (sample No.2) were used. All samples were observed morphologically by light and electron microscopes to obtain diameter and distribution of collagen fibrils in substantia propria and were performed biochemically to investigate into GAGs and collagen types. The average diameter of collagen fibrils in the intact cornea of normal, sample No.1 and No.2 was 33.2, 35.0 and 25.0 nm, respectively. The percentage of matrix per unit area was 67% in normal, 87% in sample No.1 and 28.3% in sample No.2. The type III collagen ratio was 25.3% in normal, 21.3% in sample No.1 and 35.8% in sample No.2. The relative amount of heparan sulfate, chondroitin sulfate, dermatan sulfate and keratin sulfate was 1.5, 9.7, 51.1 and 37.7% in normal, 3.3, 26.0, 45.7 and 23.7% in sample No.1 and 1.2, 18.0, 16.6 and 54.1% in sample No.2. Hyaluronic acid was found only in sample No.1 with a relative amount of 1.3%. Since there was some relationship between collagen formation and GAGs composition, it might be speculated that disturbance in arrangement of collagen fibrils and GAG metabolism especially in substantia propria would bring up opacity of the cornea.