Purpose.: To evaluate the effects of a vascular endothelial growth factor trap (VEGF Trap) on retinal vascular development and pathologic neovascularization (NV) in the canine model of oxygen-induced retinopathy (OIR).

Methods.: Newborn dogs (postnatal day [P] 1) were exposed to 100% O 2 and then returned to room air on P5. VEGF Trap (5, 25, or 250 μg) was injected intravitreally in one eye and human FC (hFc) injected in the fellow eye of air control and oxygen-treated dogs on P8. The retinal vasculature and NV were evaluated on P21. Other oxygen-exposed animals received 5 μg of VEGF Trap or hFc on P22 after confirmation of retinopathy of prematurity (ROP)–like pathology and were evaluated at P45.

Results.: In air controls, both the vascularized area of the retina and the density of superficial capillaries were reduced in 250 or 25 μg VEGF Trap–injected eyes, and deep capillaries were absent. Eyes that received the 5 μg dose were indistinguishable from controls. In oxygen-treated animals, all eyes injected with VEGF Trap exhibited markedly less intravitreal NV than that of hFc-injected fellow eyes, irrespective of dose. Retinal vascular area in OIR animals was significantly reduced in eyes injected with 250 or 25 μg of VEGF Trap, but the 5 μg dose did not inhibit retinal revascularization. Eyes with existing NV that received 5 μg VEGF Trap at P22 exhibited substantial resolution of OIR pathology at P45.

Conclusions.: The VEGF Trap inhibited the formation of NV, but higher doses also inhibited revascularization of retina when injected at P8. In contrast, the lowest dose tested effectively blocked NV and caused regression of existing NV, without appreciably affecting vasculogenesis or retinal revascularization. These findings suggest that dose selection is an important variable when considering the use of VEGF-targeting agents for the treatment of ROP.