Impairment of visual system of beagles orally ingesting clioquinol

Visual system was examined in 3 beagles given clioquinol for a long period and in 2 control beagles. Ophthalmoscopic examination revealed the decreased diameter of the optic disks of the treated dogs except for one dog. There were degenerative changes of the optic nerves in all of the treated dogs. The changes included disruption of the axons and the myelin sheaths. It was difficult to observe the morphological change of the retinae of the treated dogs. The findings demonstrate that the changes in the visual system after clioquinol administration are severe in the optic nerves rather than in the retinae.