ACUTE CALCIFICATION IN ALKALI-INJURED RABBIT CORNEA TREATED WITH SYNTHETIC INHIBITOR OF METALLOPROTEINASES (SIMP)

Purpose. The aim of this study was to evaluate the ultrastructure of a cute calcification observed in alkali-injured rabbit corneas treated w ith synthetic inhibitor of metalloproteinases (SIMP). Methods. A 12-mm alkali burn was made on the right corneas of 16 rabbits. Eight eyes w ere treated with topical phosphate-buffered SIMP, and eight control ey es were given the buffer only. Six corneas (five in the SIMP group and one in the control group) developed chalky white opacification in the central area of the cornea within 6-30 days. The corneas were excised for the following examinations: (a) light microscopy (b) energy-dispe rsive x-ray analysis, (c) electron microscopy, and (d) high-angle x-ra y diffraction. Results. The results confirmed that there was stromal c alcification in these corneas, as shown by positive van Kossa staining , needle-shaped calcium crystal aggregates, and increased calcium in t he opaque areas of the corneas. Proteoglycans in the corneal stroma of both the SIMP group and the control group significantly decreased aft er alkali burns. Very few proteoglycan filaments could be identified i n the calcified areas of the stroma. X-ray diffraction reflections wit h a Bragg spacing of 3.44 +/- 0.04 Angstrom were observed from all the calcified corneas treated with SIMP. The intermolecular spacings of c ollagen fibrils in the calcified stroma (1.24 +/- 0.34 nm) were signif icantly lower than those in the noncalcified stroma (1.64 +/- 0.04 nm) and the control corneas (1.64 +/- 0.02 nm). The results indicate that the collagen molecules within the fibrils of the calcified stroma are packed more closely than normal. Conclusion, The comparison of the x- ray diffraction patterns from the calcified corneas and chicken bone s uggests that the calcium deposits in these corneas are in a form simil ar to those found in bone. The higher rate and more extensive calcific ation in the SIMP-treated corneas may result from the inhibitory actio n of SIMP on debris processing, but the mechanism is unknown.