Cataract surgery, also called lens replacement surgery, is the removal of the natural lens of the eye (also called "crystalline lens") that has developed an opacification, which is referred to as a cataract, and usually its replacement with an artificial intraocular lens. Metabolic changes of the crystalline lens fibers over time lead to the development of the cataract, causing impairment or loss of vision. Some infants are born with congenital cataracts, and certain environmental factors may also lead to cataract formation. Early symptoms may include strong glare from lights and small light sources at night, and reduced visual acuity at low light levels. During cataract surgery, the cloudy natural lens is removed, either by emulsification in place or by cutting it out. An artificial intraocular lens (IOL) is usually implanted in its place to restore useful focus. Cataract surgery is generally performed by an ophthalmologist in an out-patient setting at a surgical center or hospital. Local anesthesia is normally used, and the procedure is usually quick and causes little or no pain and minor discomfort to the patient. Well over 90% of operations are successful in restoring useful vision, with a low complication rate. Day care, high volume, minimally invasive, small incision phacoemulsification with quick post-operative recovery has become the standard of care in cataract surgery all over the developed world. Manual small incision cataract surgery (MSICS) is popular in the developing world, as it is considerably more economical in time, capital equipment and consumables, while providing comparable results. Both procedures are low risk for serious complications. Uses Cataract surgery is the surgical removal of a lens of the eye as definitive treatment for vision impairment due to lens opacification. The procedure usually includes insertion of a prosthetic intraocular lens to restore focus within a useful range of distances. A cataract is a cloudy area in the lens of the eye that causes a visual impairment. Cataracts usually develop slowly and can affect one or both eyes. Symptoms may include faded colors, blurry or double vision, halos around lights, sensitivity to glare from bright lights, and night blindness. This may result in difficulty driving, reading, or recognizing faces. Poor vision caused by cataracts may also increase the risk of falling and depression. Cataracts are most commonly due to aging but may also be caused by trauma or radiation exposure, be present from birth, or occur following eye surgery for other