? AIM: To compare the effects on the retina inner segment and retinal pigment epithelium ( RPE ) of intravitreally injecting bevacizumab, ranibizumab and aflibercept into monkey eyes.? METHODS: Fourteen healthy cynomolgus monkeys (Macaca fascicularis, aged 3-8y,10 males,4 females) were raised at the Covance Laboratories under standard conditions. The 14 monkeys were grouped into 4 groups. Three of the groups with 4 monkeys each were injected intravitreally with one of the drugs, either bevacizumab, ranibizumab or aflibercept, while the 4th group with 2 monkeys served as a negative control. On 1d and 7d of injection, 2 monkeys from each drug treatment group were sacrificed under general anaesthesia and the 4 eyes were enucleated. All the enucleated eyes were fixed in formalin, embedded in paraffin wax, cut into 4. 0 μm sections and deparaffinized according to standard procedures. Image-Pro Plus was used for all the photos to measure the content of vascular endothelial growth factor ( VEGF) in the inner segment and RPE. The ANOVA test from JMP10. 0 statistical program was used to evaluate the results.?RESULTS:Retinal sections were checked for their anti-VEGF immune reactivity. The untreated control samples had the highest level of VEGF in the RPE and inner segment. All of these three drugs can reduce the level of VEGF in the RPE and inner segment, but Avastin seems to be more effective than Eylea in this regard. Lucentis treatment at 1d seems to be more effective than Eylea at VEGF 1d. But at 7d, both Lucentis and Eylea have the same effect on reducing VEGF expression level in the RPE and inner segment.?CONCLUSION: All of these three drugs can reduce the level of VEGF in the RPE and inner segment.