The MANF expression levels were clearly lower in the vitreous samples from patients with pure proliferative diabetic retinopathy compared with those from patients with proliferative diabetic retinopathy with vitreous hemorrhage, and this finding may be due to the mixing of the vitreous with blood, as extremely concentrations of MANF are present in the serum (Galli et al., 2016). Here, MANF is linked to proliferative diabetic retinopathy.