The Squirrel Monkey: Characterization of a New-World Primate Model of Experimental Choroidal Neovascularization and Comparison with the Macaque

PURPOSE: To evaluate and characterize the New-World squirrel monkey as a primate model for experimental choroidal neovascularization (CNV) studies and to compare it with the current Old-World macaque monkey model. METHODS: Fibrovascular tissues (FVT) were elicited in 12 maculae of seven squirrel monkeys by laser photocoagulation using optimized laser parameters (532 nm, 0.05 second, 75 micro m, 650 mW). Follow-up fundus and fluorescein angiography (FA) examinations were conducted on postlaser days 30 and 35, followed by euthanasia and histologic analysis of tissues. For comparative evaluations, FVT development also was induced and analyzed in eight maculae of four macaque monkeys with laser parameters previously used in this species (514 nm, 0.1 second, 50 micro m, 390 and 455 mW). RESULTS: FVT developed in both primate species, consisting of fibrous tissue that contained vessels that ranged from sparse but identifiable capillaries to well-established neovascular networks. Overall, 65% of the photocoagulation sites in the squirrel monkey and 37% of sites in macaque monkey elicited development of FVT. Localized FVT ranged from modest to extensive thickenings of the choriocapillaris layer. Unexpectedly, 76% of the FVT sites in squirrel monkey eyes and 27% of the sites in macaque eyes showed diffuse FVT that expanded beyond the original photocoagulation sites, accompanied by neovascular infiltration of the retina. CONCLUSIONS: Like the macaque, the squirrel monkey can be considered a useful primate model for experimental CNV investigations, while additionally offering certain species-specific advantages. Diffuse FVT permit studies of antiangiogenic therapies in areas distant from laser photocoagulative trauma sites.