 Blindness is the single most serious complication of FESS, and results from damage to the optic nerve during surgery.Serious complications such as blindness occur in only 0.44% of cases, as determined by a study performed in the United Kingdom.A Cochrane review in 2006 based on three randomized control trials concluded that FESS has not been shown to provide significantly better results than medical treatment for chronic rhinosinusitis.