by the vitreous face or IOL; Elevated intraocular pressure. Swelling or edema of the central part of the retina, called macula, resulting in macular edema, can occur a few days or weeks after surgery. Most such cases can be successfully treated. Preventative use of nonsteroidal anti-inflammatory drugs has been reported to reduce the risk of macular edema to some extent. Uveitis–glaucoma–hyphema syndrome: This is a complication of cataract surgery caused due to the mechanical irritation of mispositioned intraocular lens over iris, ciliary body or iridocorneal angle. Other possible complications include: Swelling or edema of the cornea, sometimes associated with cloudy vision, which may be transient or permanent (pseudophakic bullous keratopathy). Displacement or dislocation of the intraocular lens implant may rarely occur. Unplanned high refractive error (either myopic or hypermetropic) may occur due to error in the ultrasonic biometry (measure of the length and the required intraocular lens power). Cyanopsia, in which the patient sees everything tinted with blue, often occurs for a few days, weeks or months after removal of a cataract. Floaters commonly appear after surgery. It may be necessary to exchange, remove or reposition an IOL after surgery, for any of several possible reasons. Capsular block syndrome, which is hyper-distention of the lens capsular bag due to the IOL blocking fluid from draining through the anterior capsulotomy. This may cause a myopic refractive error; Chronic anterior uveitis, which is a persistent inflammation of the anterior segment; Chronic loss of endothelial cells faster than the rate due to normal aging; Iris pigment epithelium loss; Pain; Progressive elongation of the pupil in direction of the long axis of the IOL; Progressive closing of the anterior chamber angle due to propagation of anterior synechiae without apparent anterior uveitis; Incorrect IOL refractive power; Incorrect positioning of the IOL, including decentering, tilt, or rotation that reduces correct function; Damage or deformation of the IOL; Unexpected optical results due to defects of the IOL; Undesirable optical phenomena reported by the patient due to any other cause. Risk Statistically, cataract surgery and IOL implantation are procedures with the safest and highest success rates in eye care. However, as with any type of surgery, some level of risk remains. As of 2011, cataract surgery is the most frequent surgical procedure in the United States, with 1.8 million Medicare beneficiaries undergoing the procedure in 2004. This rate is expected to increase as the population ages. Cataract surgery