EFFECT OF MITOMYCIN-C ON THE OPTIC-NERVE IN RABBITS

Aim-To prevent scarring after surgical optic nerve sheath decompressio n, it has been suggested that treating the area of fenestration with m itomycin C (MMC) might be effective. An animal model was used to test whether this toxic substance may cause optic neuropathy. Methods-The o ptic nerves of 15 rabbits were exposed to balanced salt solution (BSS) or mitomycin C (MMC) in a concentration of 0.2 or 0.5 mg/ml. The unop erated fellow eyes and the eyes that received BSS served as controls. Steady state visual evoked potentials (VEPs) at 40, 50, and 60 Hz were recorded before and 4 weeks after surgery. The nerves were examined b y light and electron microscopy after 5 weeks. Results-VEPs in all non -operated eyes and eyes treated with BSS before and 4 weeks after surg ery demonstrated responses at all three stimulus frequencies tested. E yes operated with MMC had extinguished responses for one, two, or all the different temporal frequencies after 4 weeks with marked reduction in VEP amplitude. Eyes operated with MMC at a concentration of 0.5 mg /ml had significantly more reduced VEP responses than those where MMC 0.2 mg/ml was used. On histopathological examination, special stains f or myelin and axons showed normal axons and myelin. On electron micros copy, no distinct abnormalities were seen among nerves operated with M MC and controls. Conclusion-The data from this study suggest that in r abbits, the application of MMC to the optic nerve has a dose dependent toxic effect in the short term postsurgical follow up period. While a functional alteration could be demonstrated reproducibly by steady st ate VEPs, the extent was not obvious on histopathological examination of the nerves.