Cataract surgery is the removal of the lens of the eye (also calle "crystalline") that has developed an opacification, which is referred to as a cataract. During cataract surgery, a patient's aging and cloudy natural lens is removed and replaced with a synthetic lens to restore the lens's transparency. Metabolic changes of the crystalline lens fibers over the time lead to the development of the cataract and loss of transparency. Following surgical removal of the natural lens, an artificial intraocular lens implant is inserted (eye surgeons say that the lens is "implanted"). Cataract surgery is generally performed by an ophthalmologist (eye surgeon) at an ambulatory (rather than inpatient) setting, in a surgical center or hospital, using local anesthesia (either topical, peribulbar, or retrobulbar). 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-op recovery has become the standard of care in cataract surgery all over the world.