In cataract the human lens inside the eye becomes frosted or opaque when "mature" .It is taken out and replaced with an artificial lens. When ever the vision is obstructed enough due to cataract, the cataract is fit to be taken out. In the past we could operate only on advanced cataracts. But it is not so any more. Cataract generally comes in the eyes of the elderly but can appear at any age. They appear more frequently after injury to eye, in diabetes or in other eye disease. Some families tend to develop cataract at an early age. Generally after surgery there is good visual recovery. Surgeons use either phacoemulsification where ultrasound is used to liquefy the human lens and bring it out through a small incision or SICS where the human lens is brought out by hydraulic pressure through a somewhat larger incision but avoids ultrasound energy which can be toxic to the eye at high levels. An artificial lens is then inserted. These come in a variety of designs and variety of materials. Each surgeon has his preferences of intraocular lens but in some Medical Centers the patient might be asked to choose. The choice is best left to the surgeon.