Cataracts are characterized by opacity of the crystalline lens of the eye and are the primary cause of preventable blindness in the world. They may be congenital or age related; secondary to exposure to drugs, toxins, or radiation; or the product of various metabolic diseases. Visually significant cataracts are a major public health issue and are found in 50% of persons 65 to 74 years of age and 70% of persons 75 years of age or older.
Modern cataract extraction with placement of an intraocular lens (IOL) is a highly effective and efficient operation to restore visual acuity and contrast sensitivity in patients with severe cataracts. Presently, the operation has evolved to the point where it involves constructing a small (2.5–3.5 mm) wound at the edge of the cornea. The incision is carefully shelved to minimize leakage through the wound, viscoelastic material is injected into the anterior chamber to protect the cornea, and the anterior capsule of the lens is removed. An ultrasound probe (phacoemulsification tip) is then inserted into the anterior chamber and used to fragment and remove the cataractous lens, though the capsule of the lens is left intact except for a small opening in the anterior portion through which the phaco tip had been inserted. An IOL with appropriate focusing power to neutralize any refractive error is chosen based on the size and corneal curvature of the patient's eye.