Fluorescence of the optic discs of rhesus monkey. (A) Right optic disc one hour after intravenous injection of 1 ml 25% fluorescein shows optic disc fluorescence, with fluorescent outline of the retinal vessels. (B-D) Right eye is after injection of 1 ml 25% fluorescein solution into cisterna magna, after release of same amount of cerebrospinal fluid. B through D show progressive intense fluorescence of the optic disc ½, 1, and 1½ hours, respectively after the injection. At 3½ hours after injection, both optic discs were intensely fluorescent and no fundus details were visible. (Reproduced from Hayreh SS. 1977a)