The capillary pattern of the rat optic nerve can be demonstrated in sections incubated to show alkaline phosphatase activity and by perfusion with dyed silicone rubber. In the nerves of one third of the rats studied, a capillary-poor zone was found several millimeters behind the globe. This anomaly may explain the frequency and distribution of lesions induced in the rat optic nerve with cyanide.
Lessell S. Capillaries of Rat Optic NerveRelationship of Anomalies to Cyanide Lesions. Arch Ophthalmol. 1974;91(4):308-310. doi:10.1001/archopht.1974.03900060318015