C1QTNF9 and proliferative diabetic retinopathy: In addition, serum Ephrin-A1 in proliferative diabetic retinopathy patients was higher than that in non-proliferative diabetic retinopathy patients, and CTRP9 level was lower than that in non-proliferative diabetic retinopathy patients (Gao et al., 2017; Zhou et al., 2021).