EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
Issue link: https://digital.eyeworld.org/i/153099
32 EW FEATURE February 2011 Diagnostic technologies for cataract surgery August 2013 Diagnostic tools' use increasing by Michelle Dalton EyeWorld Contributing Writer AT A GLANCE ¥ Manual Ks are helpful, but topography is necessary to rule out irregularities. ¥ Topography analyzes the qualitative aspects of the cylinder. ¥ Sophisticated technology can help reduce enhancement rates to low single digits. The more sophisticated the technology, the better to evaluate patients with astigmatism P atients with pre-existing astigmatism need a battery of tests before undergoing cataract surgery —tests that can help surgeons determine what axis the astigmatism is on, the magnitude of the astigmatism, and the amount of irregularity of the astigmatism. A decade ago, manual Ks were commonly used, said Jeffrey D. Horn, MD, in private practice, Vision for Life, Nashville, Tenn. In those days, he'd use the plus sign on the manual keratometer for both axes, but would also include Orbscan (Bausch + Lomb, Rochester, N.Y.) readings and topography "to make sure that there wasn't any irregularity to the astigmatism." These days, however, manual Ks alone just don't cut it. "You cannot effectively, consistently treat preoperative astigmatism with only a manual keratometer, period. The reason is it cannot adequately determine irregular or asymmetric astigmatism," said Kevin Waltz, MD, in private practice, Eye Surgeons of Indiana. "Our job is to figure out whether the astigmatism is corneal or lenticular or a combo of both of those things. Usually my cataract patients get diagnostic topography to give me an idea of whether or not the manifest refraction matches their keratometric cylinder," said Sonia Yoo, MD, professor of ophthalmology, Bascom Palmer Eye Institute, Miami. Keratometers are typically set around 2.6 mm, "so they're very good for the central cornea, but not very good at the mid-periphery points," Dr. Waltz said. "You need topography to look at the qualitative aspect of the cylinder." William Trattler, MD, in private practice, Center for Excellence in Eye Care, Miami, is a fan of using topography to help confirm the axis of astigmatism and the quantity of the astigmatism in addition to irregularities, including asymmetry. "It also helps determine if there is any dryness; you can see the quality of the tear film just by looking at the maps," he said. Consistency in numbers is the driving force behind numerous tests patients undergo at Wallace Eye Associates (Alexandria, La.), said R. Bruce Wallace III, MD, founder and medical director. He wants to ensure the axis matches properly, the corneal cylinder matches, and if they don't, "we tell patients they'll likely need an astigmatic correction, and if the cylinder is low enough, we'll do the limbal relaxing incision in conjunction with the cataract surgery," he said. Robert T. Crotty, OD, clinical director, Wallace Eye Surgery, said in general, the group uses autorefractors, corneal topography, K readings from an IOLMaster (Carl Zeiss Meditec, Jena, Germany) "to make sure the dioptric values correlate with each other, and in some cases we'll even throw in manual keratometry for reassurance." Manual Ks are not obsolete, however. Dr. Horn still defers to his manual keratometer when there are "significant differences" between the topographer, refraction, Lenstar (Haag-Streit, Koeniz, Switzerland), and Pentacam (Oculus, Wetzlar, Germany) readings, or when those readings "constantly change from visit to visit." The symmetry of any K reading is equally important, Dr. Trattler said. Variability in corneal readings is likely a result of an unstable ocular surface, he said. Dr. Crotty added any patient with an irregular ocular surface is deferred for treatment; more severe ocular surface disease, such as those with degenerative scar tissue may even require superficial keratectomy to improve the outcomes of cataract surgery. Dr. Wallace relies on his whole team to sign off on all charts, calcu- lations, and even toric IOL choices before the preop evaluation is considered complete. "There have been times when one of us has caught a mistake that would have resulted in a poor visual outcome," he said. Flow of events With normal topography, using the K readings from an IOLMaster "works quite well," Dr. Waltz said, but the device will only check a limited number of points. Comparatively speaking, the Lenstar checks 32 points, "so it enhances your ability to pick an IOL correctly." Dr. Trattler opts to bring patients back for a second reading to reconfirm the initial findings and rolls the costs into his premium packages. Dr. Yoo performs the topography and wavefront aberrometry in the clinic, but the IOLMaster readings are reserved for the preop exam day (as the device is not in the clinic). Dr. Horn prefers the Lenstar and allows for a small amount of deviation (less than –0.2 D for the astigmatism and less than 3 degrees for the axis), and uses the Holladay II formula for IOL calculations. "The iTrace [Tracey Technologies, Houston] is a great diagnostic device to decide where the aberrations are coming from to quantify the astigmatism," Dr. Waltz said, noting the device's ability to superimpose the image with the topography to help ensure lens positioning is correct in the OR. Cost issues Toric lenses are more expensive, and these diagnostic tools have a hefty price tag as well—but not really, Dr. Waltz explained. For practices converting 10% of their cataract patients to premium lenses, the cost involved with the extra diagnostic devices is rapidly returned. If surgeons only perform 100 or so cases a year, even with an enhancement rate of 10% "that's only 10 cases a year, so you probably deal with it and move on. But once a practice is at 1,000 procedures a year, now that 10% enhancement rate results in 100 cases, and you'll need to drive down those rates," he said. "As the rate of toric and multifocal IOLs increases, spending larger amounts of money on better technology to reduce enhancement rates makes a lot of sense." Dr. Waltz believes more cataract specialists need to start thinking like their refractive specialist counterparts. "When my LASIK enhancement rate was 30% I wasn't as concerned with enhancements because I expected them. But when my LASIK enhancement rate dropped to 10%, patients were more upset about needing an enhancement and I was more concerned. Now that my LASIK enhancement rate is 2%, those patients who need enhancements think I did something wrong. So, paradoxically, I work harder to further reduce my 2% enhancement rate than I did to reduce my 30% Topography can help confirm the axis of astigmatism and the quantity of the astigmatism in addition to irregularities, including asymmetry. Source: Christopher Hodge, Vision Eye Institute