The plasma ET-1 levels were higher in the POAG group than in the control group, with a mean difference of 0.63 pg/mL [p = 0.02, 95% CI = 0.12–1.15]; however, there was significant heterogeneity across the 6 studies (I2 = 86%, p < 0.00001) (Figure 3). Here, EDN1 is linked to open-angle glaucoma.