SERPINF1 and proliferative diabetic retinopathy: Even though RPE cells secrete PEDF constitutively, the amount secreted in pathological conditions, such as AMD, is apparently not sufficient to control the neovascularization; in fact, PEDF levels have been found to be significantly lower in the vitreous of eyes from patients with proliferative diseases such as proliferative diabetic retinopathy (PDR) and AMD than in the vitreous of normal eyes [116, 117].