Optic neuropathy following simulation of orbital hemorrhage in the nonhuman primate.

The goal of the study was to determine, using a nonhuman primate (NHP) model, the minimum duration of elevated intraocular pressure (IOP) (induced by an inflated catheter) necessary to produce significant visual system deficits. In Old World monkeys (Macaca mulatta), a catheter was placed retrobulbarly in one orbit and inflated with saline for either 180 min (10 monkeys) or 240 min (six monkeys subjects). Baseline color fundus photographs, monochromatic photography, fluorescein angiography, and IOP measurements were performed preoperatively and at either 2, 4, or 6 weeks postoperatively on both eyes of each monkey prior to killing and histological analysis. Optic neuropathy was demonstrated in eight of these NHPs. In the two most severe cases (240 min inflation condition), complete nerve fiber atrophy with central retinal artery occlusion was observed. Sector nerve fiber atrophy, extending from the temporal disc to beyond the macula, was noted in the other six monkeys, five of which were in the 180 min inflation condition. Thus, optic neuropathy, sufficient to produce visual loss, was noted following increased IOP (> or = 50 mm Hg) for 180 min or 240 min. These data emphasize the need for timely intervention to mitigate the potential detrimental effects of retrobulbar hemorrhage when it occurs in humans.