Eyeworld

EW CATARACT 42 by Shamik Bafna, MD Study shows that scanned-capsule centration offers the best chance of 100% capsule-optic overlap T he capsulorhexis is a critical element of cataract sur- gery. Not only does it set the stage for everything that follows, but it plays a key role in IOL positioning. A too- small or too-large capsular opening can potentially, over time, lead to anterior or posterior displacement of the lens optic and a change in the effective lens position (ELP). Even when there is no frank displacement of the lens, uneven capsular contrac- tion around the lens optic can cause it to be slightly tilted, potentially inducing aberrations or reducing the quality of vision, especially with a multifocal IOL. Warren Hill, MD, has shown that the greatest surgical infl uence on ELP is the capsule opening, advocating that the capsulotomy be round and slightly smaller than the optic, with 360-degree overlap of the optic edge by the capsule, in order to meet the demands of modern refractive cataract surgery. 1 Femtosecond lasers offer a high degree of precision and may make it Capsulotomy centration in laser cataract surgery easier to create a "perfect" capsular opening. The fi rst step has been to ensure that these lasers can make a complete and free-fl oating capsulot- omy with no capsule tags. Surgeons still report diffi culty with this on certain laser platforms. Published analyses have shown greater con- sistency in size and circularity with femtosecond laser capsulotomies. 2–4 Nagy and colleagues reported fewer cases of incomplete capsule overlap in a group of femto patients (11%) compared to manual capsulorhexis patients (28%) 3 and a lower rate of IOL decentration in the laser group. 4 Indeed, the use of these lasers completely changes what is possible for us to do, raising a lot of ques- tions about the "ideal" capsulotomy along the way. Capsulotomy centration study The femtosecond laser system that my colleagues and I use, the Catalys system (Abbott Medical Optics, AMO, Santa Ana, Calif.), allows the surgeon to choose among several methods for positioning the capsu- lotomy, including centering based on the pupil, the limbus, or the scanned capsule; decentering the opening using a custom setting; and maximizing it for the largest possible capsulotomy. Figure 1: Looking at the capsulotomy options with respect to the IOL implanted here, one can see that the scanned capsule-centered capsulotomy (purple) is better centered over the optic than the pupil-centered capsulotomy (green) would have been. Source: Shamik Bafna, MD continued on page 44 September 2014 If the pupil center represents the center of the visual axis (an assump- tion that may not always be correct), then it would be ideal to center the capsulotomy—and the IOL—on the pupil. Pupil centration also matches how most surgeons create a capsu- lorhexis manually. Scanned-capsule centration is a unique capability of the Catalys system. The laser maps the capsu- lar surfaces based on full volume, three-dimensional optical coherence tomography (OCT) imaging of the anterior and posterior capsule. Based on these surface fi ts, the center of the capsule is identifi ed and then projected onto the anterior capsular surface, and a capsulotomy of the specifi ed diameter is automatically positioned around that centration point. Given that an IOL's spring- like haptics naturally center the im- plant within the anatomical dimen- sions of the capsule (without regard to the optical center), it makes sense to me to also create the capsulotomy in the center of the capsule, so that the optic anchored in the cap- sule will be similarly centered and symmetrically aligned behind that opening. We decided to compare how 2 of these methods (pupil-centered and scanned capsule) perform for routine use. To test the 2 approach- es, we randomly used one method or the other in 50 consecutive eyes. Preoperatively, the surgeon can fl ip back and forth to view the outlines of both the pupil-centered and scanned capsule-centered capsuloto- my. Regardless of which method was used, we programmed the laser to create a 5.1-mm capsulotomy in all cases. Complete capsulotomies with no tags were achieved in all eyes. IOLs were implanted and centered to the best of our abilities in all cases. Postoperatively, we analyzed the position of each IOL relative to the capsular opening and assessed the degree of capsular overlap. Using the raw video footage from the laser and operating room video, we deter- mined whether the alternate meth- od (e.g., scanned capsule in an eye with a pupil-centered capsulotomy) would have improved or worsened centration of the capsulotomy over the implanted optic. In some eyes, the 2 methods resulted in quite different locations for the capsulotomy. Looking at the capsulotomy options with respect to the implanted IOL in the case in Figure 1, one can see that the scanned capsule-centered

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