Figure 1. Box plot representing OPN levels in patients without DR, patients with NPDR, and patients with PDR. Compared with the median in patients without diabetic retinopathy (DR; 51.7 (38.9–66.9) ng/ml), the median of the OPN level is statistically significantly higher in patients with non-proliferative diabetic retinopathy (NPDR; 61.7 (47.7–87.3) ng/ml, p<0.001) and patients with proliferative diabetic retinopathy (PDR; 76.8 (55.00–103.6) ng/ml), p<0.001). The OPN level is also statistically significantly higher in patients with PDR than in patients with NPDR (p=0.017; Wilcoxon rank-sum test).