When calculating the ratio of non-perfusion area of SCP to DCP, both CNP ratio (5.65 ± 5.83 vs. 7.85 ± 6.96, p = 0.728) and GPD ratio (3.61 ± 1.80 vs. 4.20 ± 1.91, p = 0.417) were lower in eyes with diabetic macular edema. Here, CNP is linked to diabetic macular edema.