PURPOSE: The purpose of this study was to identify a correlation between engorgement of the vortex vein and the development of polypoidal choroidal vasculopathy (PCV).METHODS: Engorgement of the vortex vein was evaluated by masked observers using a montage of indocyanine green angiography images.Sixty-three eyes with PCV, 27 uninvolved fellow eyes with PCV, and 30 eyes of age-matched control subjects were included.The incidence and distribution pattern of engorgement were evaluated.RESULTS: Thirty-three eyes (52.4%) of PCV evidenced engorgement of the vortex vein, whereas such engorgement was detected in only 7 of the 30 eyes (30.4%) of the control subjects (P = 0.016).Among 27 fellow eyes with PCV, it was detected in 11 (40.7%) (P = 0.706 vs.control eyes).In all groups, it was most frequently detected at the inferior temporal quadrant.In eyes with PCV, mean (±standard deviation) choroidal thickness of the eyes evidencing vortex vein engorgement was 338.1 ± 131.3 μm and the thickness of those not evidencing vortex vein engorgement was 275.1 ± 107.7 μm.When the choroidal thickness increased to 10 μm in the eyes with PCV, the odds of detecting the engorgement was multiplied by a factor of 1.05 (P = 0.042).The incidence of the engorgement of vortex vein was correlated with the presence of choroidal vascular hyperpermeability (P = 0.009).CONCLUSION: This study demonstrates that engorgement of the vortex vein was observed more frequently in the eyes with PCV.Such a finding was associated with choroidal thickening and choroidal vascular hyperpermeability.These indicate that the engorgement of the vortex vein might be involved in the pathogenic mechanisms of PCV.