Aberrant nerve fibre bundles in the retina of the dog.

Systematic ophthalmoscopic examinations of 2511 Beagles, test animals in 72 long-term toxicological studies, showed archiform thin white stripes in the fundi of 98 animals (3.9%). The stripes occurred in one or both eyes in the non-tapetal fundus of the two lower quadrants. Examinations of the fundus of some dogs by fluorescence angiography and ophthalmoscopy with red-free light showed that these fibriform stripes were in the retina. Histological examination showed these stripes to be nerve fibre bundles (5-120 axons) lying at the ganglion cell layer. The ultrastructure of the fibres did not differ from that of the nonmyelinated neurites of the fibre layer. The stripes may be retinal nerve fibres with a normal structure but could be distinguished from fibres of the nerve fibre layer by their intraretinal location and by their course.