Phosphate buffer in alkali eye burns as an inducer of experimental corneal calcification

Corneal calcification is a common problem in severe inflammation, chronic glaucoma, renal disorders and other diseases with disturbed calcium and phosphorus metabolism. The pathogenesis of corneal calcifications in ocular diseases is not yet completely understood. We present a model of an induced corneal calcification by local treatment. In a double-masked experiment 16 rabbits underwent eye burn of one cornea followed by immediate rinsing (160 ml) with isotonic phosphate buffer (n=8) or saline solution (n=8) three time a day for 16 days. Tissues were excised, shock frozen and cut into 10 microm slices, freeze dried and coated with evaporated carbon. In the phosphate buffer group an early onset of corneal opacification occurred resulting in completely white corneas after 16 days, combined with corneoscleral ulceration. The other group showed similar corneal erosion and a little corneal ulceration, but no opacifications. The opacifications of the phosphate buffer group could be identified as calcifications by direct measurements of calcium and phosphate (by energy dispersive X-ray analysis on corneal samples). In conclusion, inappropriate application of phosphate leads to uncontrolled calcifications of the cornea after severe burns to the eye. This reflects clinically observed calcifications after eye burns and possibly the adverse side effects of phosphate buffered eye drops being applied in ophthalmology.