VEGFA and Patent ductus arteriosus: After analysis of a number of clinical studies, Cousins and colleagues identified 2 distinct morphologic phenotypes of the pathologic new blood vessels in patients with AMD: one is the capillary subtype that is highly responsive to anti-VEGF therapy and rarely exhibits PDA; the other is the arteriolar subtype that is closely associated with PDA and mediates anti-VEGF resistance [11].