AIM:To investigate the visual impact of sub-Tenon anesthesia during combined phacoemulsification and vitrectomy surgery.METHODS:In this prospective case series, consecutive patients who underwent combined phacoemulsification and pars plana vitrectomy (PPV) under sub-Tenon anesthesia between October 2008 and September 2009 were enrolled. The patients were asked whether they could see the light of the operating microscope or not between various surgical steps with their contralateral eye being covered.RESULTS:A total of 163 eyes of 163 patients were enrolled in this study. After their contralateral eyes were covered, 152 (93.3%) patients said that they could not see any light at least during one of the surgical steps. All eyes recovered to at least light perception on the first postoperative day. The incidence of no light perception during the surgery was not related to demographic factors, including age, gender, or type of ocular diseases.CONCLUSION:The incidence of no light perception during combined phacoemulsification and vitrectomy under sub-Tenon anesthesia was high in our study. Patients should be duly informed about this temporary but potential intraoperative event.