[Chronic toxicity of tobacco smoke on the visual system].

The chronic toxicity of tobacco smoke on the rats visual system was studied. Six male Wistar rats had been subjected to five hour's daily passive smoking of 15 cigarettes for 52 weeks, in an attempt to produce tobacco amblyopia. Elongation of the peak latency time of N1 and P1 waves in the visual evoked potential (VEP) was recognized. Histopathologically, some degree of glial proliferation and pyknosis was observed in the optic nerves of all treated rats, and massive disappearance of nerve fibers was seen in one severely affected case. Electron microscopic examination proved that unmyelinated nerve fibers increased in number and the myelin sheath was thinner than that of the untreated control rats, while axons were relatively well preserved. The distribution in the magnitude of the axon diameter histogram was shifted towards a smaller diameter than that of the control rats. Electroretinography (ERG) did not show any significant changes of the latency and the amplitude of both a- and b- waves, and no histopathological changes were seen in the sensory retina. Neither functional nor histological changes were seen in the sciatic nerves. These results indicated that the optic nerve is thought to be more vulnerable to tobacco smoke than the peripheral nerves and we consider that a primary change of the nerve is demyelination at the retrobulbar portion of the optic nerve.