Effect of methyl isocyanate (MIC) gas on the eyes of Fischer 344 rats.

The accidental release of methyl isocyanate gas in Bhopal, India, was reported to cause temporary blindness and other eye injuries in many of the exposed people. Methyl isocyanate (MIC) is known to be corrosive and to irritate intact skin and mucous membranes, but little is known about the extent of ocular damage incurred during exposure to its vapors. The eyes of male and female Fischer 344 rats were evaluated immediately after a 2-hr exposure to 0, 3, 10, or 30 ppm of MIC, and periodically thereafter during a 91-day recovery period. During exposure to 10 ppm and higher concentrations, rats kept their eyes partially closed. Copious lacrimation and occasional frothy nasal discharge were evident. Eyes were examined under ultraviolet light after topical application of sodium fluorescein, and histopathologic examination included lids, cornea, lens, retina, optic nerve, and Harderian gland. There was no significant gross or microscopic evidence of epithelial erosion or ulceration of the cornea, or of adjacent tissues immediately after, or at any time following exposures. No skin irritation was noted. It would appear that the natural protective mechanisms of the eye of rats were adequate to prevent ocular damage at these exposure levels.