A cataract is a clouding of the natural lens, the part of the eye responsible for focusing light and producing clear, sharp images. The lens is contained in a sealed bag or capsule. As old lens cells die, they become trapped within the capsule. Over time, the cells accumulate, causing the lens to cloud and making images look blurred or fuzzy. Cataracts are a natural result of the aging process, but may also be caused by diabetes. Occasionally, they are present at birth.

The most common symptoms of cataracts are a gradual decrease in vision and glare. Usually the decision to remove a cataract is based on the symptoms - once a person can no longer see well enough to do regular activities. Surgery is often performed on an outpatient basis. Using a local anesthetic, an incision is made and the opacified lens is removed. A clear, intraocular lens implant is inserted in its place. After surgery, new glasses are generally required.