Histopathological study of canine optic nerve retina treated by organophosphate pesticide.

The fine structure of pathological changes was examined in the optic nerve and retina of beagle dogs after oral administration by capsule of the organophosphate pesticide ethylthiometon for 2 years. The optic nerve was invariably affected, and the number of myelinated axons markedly reduced. These were substituted for by delicate processes of astrocytes. Changes in the retina were mild and mainly seen in the peripapillary pigment epithelial cells and in the Müller cells of the peripheral retina. These histopathologic findings indicate that long-term administration of ethylthiometon involved both the optic nerce and selected portions of the retina.