All patients underwent a 23- or 25-gauge pars plana vitrectomy. The primary outcome of the study was the measurement of EPO and VEGF concentrations in serum and vitreous and aqueous humor. Blood samples, taken before surgery, were centrifuged at 3000 rpm for 10 minutes to separate the serum fraction, which was stored at -80°C. Aqueous and vitreous humor were taken during the surgery and immediately frozen at -80°C. Both EPO and VEGF concentrations were measured in serum and vitreous humor; however, owing to the small amount of sample, only EPO concentrations were determined in aqueous humor. EPO was assayed by radioimmunoassay (Immulite EPO 200, Siemens), with the lowest detection limit of 1.0 mIU/mL. VEGF was assayed by ELISA (Human VEGF Immunoassay, R & D Systems Europe, Abingdon, UK) with a lower limit of detection of 10.0 pg/mL. VEGF concentrations below the lower limit of detection were set to 5 pg/mL to perform statistical analysis. VEGF values above 2000 pg/mL were set to 2500 pg/mL; statistical tests were also performed after deleting the data above 2000 pg/mL.