Topically administered indomethacin was found to reduce the occurrence of cystoid macular edema after lens extraction. Indomethacin was given topically as 1% oil solution (sesame oil) eye drops twice or three times daily from the day before operation to the 40th day after operation. This effect suggests that prostaglandins play a leading role in the development of this disorder. It is postulated that operative irritation causes production of prostaglandins, which disrupt the blood-aqueous barrier, followed by an increase of the inflammatory mediators and debris in the aqueous. These inflammatory substances and prostaglandins themselves diffuse from the aqueous into the posterior pole of the fundus, where they induce inflammatory changes in vascular permeability in the perifoveolar capillary plexus. Clinically the cystoid macular edema then develops.