GSTM1 and diabetic retinopathy: Despite limited clinical evidence correlating DPN to Hb or erythrocyte deformability, previous cross-sectional studies have investigated the association of erythrocyte deformability with diabetic nephropathy and retinopathy and indicated that impairment in erythrocyte deformability is associated with loss of renal function and the risk of diabetic retinopathy in patients with diabetes [11–13].