Cataract surgery

Cataracts are characterized by opacity of the crystalline lens of the eye. They represent the primary cause of treatable blindness in the world. Cataracts are generally categorized as congenital or age related; however, they may also result from exposure to drugs, toxins, or radiation; or be the product of various metabolic diseases. Visually significant cataracts are a major public health issue: they are found in 50% of persons 65–74 years of age and 70% of persons 75 years of age or older. Modern cataract extraction is accompanied by insertion of an intraocular lens (IOL). It is a highly effective and efficient operation that restores visual acuity and contrast sensitivity in patients with visually significant cataracts. Presently, the operation employs a systematic, minimally invasive approach which involves creating a small (2.5–3.5 mm) wound at the edge of the cornea. The incision is carefully created in a beveled manner that minimizes leakage through the wound without sutures. A viscoelastic material is injected into the anterior chamber to protect the cornea and to maintain a working chamber in the eye for instrumentation. Next, a portion of the anterior capsule of the lens is removed to allow access to the lens cortex and nucleus, creating a circular opening in the capsular bag (capsulotomy). An ultrasonic probe (phacoemulsification tip) is then inserted through the anterior chamber and capsulotomy, into the lens. The energy generated at the tip of the probe is used to fragment and remove the cataractous lens nucleus and cortex. The remaining capsule of the lens is left intact (referred to commonly as the capsular “bag”). A custom IOL is selected, with appropriate focusing power to neutralize the refractive error. The measurements are based on the axial length of the eye as well as the corneal curvature. Most lenses are folded and inserted through the incision into the “bag,” where the lens can then unfold and rest in the location of the original native lens. After the instruments are removed, the wound is self-sealing and watertight. Occasionally, one or more sutures are required to secure the wound. Despite the highly technical aspects of cataract surgery, experienced surgeons can perform the operation in 30 minutes or less.