Relative hypotony in the affected eye was present in 40% of patients with uncomplicated unilateral retinal detachments. The average pressure asymmetry was only 1.3 mm Hg, but in one out of every four patients the difference was 3 mm Hg or more. In a control group, such a difference occured in only one out of every twenty patients. Relative hypotony persisted for longer than six months after scleral buckling operation, occuring even in patients that did not exhibit hypotony preoperatively.