ImPairmentof choroidal Perfusion was found in age-related macular degeneration(AMD) Patients. We Postulatedthat vasoactive agents, which can reduce choroidal blood flow resistance, might Preventthe develoPmentof choroidal neovascularization (CNV). D-Timolol and L-Timolol are hyPotensive agents used in cardiovascular and glaucomatheraPy.their effectson laser-induced exPerimental CNV rat model and human umbilical vein endothelial cells (HUVEC) werethus evaluated. ·METHODS: Male Brown Norway rats were anesthetizedto receive Nd:YAG laserto breakthe Bruch's membrane. D-Timolol and L-Timolol were givenonce dailythrough intraPeritoneal injection after lasertreatment for 4 weeks. Fluorescein angiograPhy(FA) was Performedon 2 weeks and 4 weeks. HUVEC weretested by Proliferation assay and adhesion assay with D-Timolol and L-Timolol at different concentrations. ·RESULTS: D-Timolol reducedthe fluorescein leakageto 83%ofthe control grouP in laser-induced rat's CNV model at a dosageof 15mg/(kg·d). L-Timolol had no effecton CNV formation even at a higher dosageof 20mg/(kg·d). D-Timolol inhibitedthe endothelial cells Proliferation significantly by 300mg/L. L-Timolol also significantly inhibitedthe cell Proliferation at 1 000mg/L. But at a lower dose such as 300mg/L, no significant inhibitory effect was found. Both drugs showed no effecton cell adhesion function in cell culture exPeriments. ·CONCLUSION: D-Timolol was foundto Prevent CNV develoPment in laser-induced model in vivo and inhibit vascular endothelial cells Proliferation in vitro . L-Timolol had no effecton cell Proliferation atthe same dose, and neitheron rat CNV model.the results indicatethesetwo isomers have different functionson rat's CNV Prevention andon HUVEC cell Proliferation.