A capsulorhexis is a continuous circular incision created by a cataract surgeon in the anterior surface of the human eye lens capsule to allow for removal of a cloudy lens. The lens capsule, an elastic, transparent membrane made up of collagen that surrounds the lens, holds the lens in proper position in the eye and molds its shape during near vision activities, such as reading. When a lens becomes cloudy due to age, trauma, or steroid use, a capsulorhexis is performed using a needle or forceps to create an opening in the capsule that is approximately 4.0 to 5.5 millimeters(0.15 to 0.20 inches) in diameter. After the opaque natural lens is removed using ultrasound, an implant or artificial lens is inserted in the capsular bag through the hole in the capsule. An ideal capsulorhexis produces an aperture with a smooth, stable circumference that overlaps the artificial lens by at least 0.5 millimeters(0.02 inches), with the edges of the implant completely covered.
The surgeon initiates the capsular tear with a central cut through the elastic membrane using a needle, called a cystotome. At the end of the cut, the needle is pushed or pulled to form a flap in the membrane that folds over itself. The back surface of the flap is engaged and directed with a forceps or the needle, with traction exerted in a circular direction. Once a continuous incision is completed all the way around in a circle, the free central island torn from the membrane is removed using the forceps. During the course of the capsulorhexis, a viscoelastic gel is inserted into the eye to push the lens in a posterior direction, maintaining tension on the capsule and enhancing control of the direction of the incision.
A successful capsulorhexis is a critical step in ensuring a good cataract surgery outcome. It allows fluid to be introduced through the hole and channeled between the capsule and the cloudy lens, facilitating its removal. The smooth curvilinear tear prevents the formation of radial tears in the capsule that may dissect to the back of the capsule, causing the lens to drop backward into the eye. Other purported benefits of the capsulorhexis include decreased clouding of the capsule after the surgery and better centration of the implant postoperatively. For these reasons, the majority of cataract surgeons prefer the continuous curvilinear tear to the older can-opener capsulotomy, during which the opening was created by making punctures in a circle with the needle.