AUG 2014

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

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Page 45 of 82

43 EW FEATURE purpose of maintaining a more prolate shape of the cornea." With other conventional ablations, Dr. Hamilton said the cornea ends up in a more oblate shape, which can cause a lot of spherical aberration and night vision problems. Topography-guided ablations are similar in concept to a wave- front-guided treatment, but Dr. Hamilton said that it makes more sense to do a topography-guided treatment. "With wavefront, you end up taking into account information from the lens, which is constantly changing throughout life," he said. iDesign The iDesign is the next generation of wavefront-guided technology. Dr. Hamilton said that it has higher resolution data, with thousands of data points instead of hundreds, and it provides more accurate wavefront- guided treatments. One of the issues with wave- front-guided treatments is that, particularly with certain platforms, it can be hard to capture some irreg- ular corneas, Dr. Hamilton said. The iDesign offers a solution to this be- cause it is a more robust and higher resolution system. CATz The CATz program (custom aspheric treatment zone) was FDA approved a few years ago, reviewed again, and approved for clinical use for myopia and astigmatism in Sept. 2013, Dr. Waring said. It operates on Nidek's NAVEX Quest laser system. The "custom" part of CATz refers to topographically guided treatment for patients. "It's the only topographically guided FDA ap- proved laser in the U.S. that is being actively used now," Dr. Waring said. This customizes treatment for each patient's corneal shape, based on topographic elevation maps, treating asymmetries and irregularities. "Aspheric" refers to CATz adjusting for the changes in radial ablation efficiency. A laser hitting the center cornea acts differently from one hitting the paracentral or peripheral cornea because there's a different curvature, Dr. Waring said. In the paracentral cornea, the laser hits obliquely, but in the center, it hits perpendicularly. You have to adjust the laser energy so the paracentral pulses have a little more energy than the central to create a more prolate postoperative topog- raphy with less induced spherical aberration, he said. Finally, the "treatment zone" means there is no distinction between optical zone and the transition zone because with the CATz program, it's one continuous aspheric, 8.5-mm diameter ablation zone. Dr. Waring said this makes the treatment more prolate with better optics. The CATz platform is based on the refractive, Placido topographic, autokeratometric measurements taken by the OPD (optical path difference), a standalone diagnostic instrument that allows the surgeon to create a simulated postoperative topography target before surgery. The target presents a more regular, symmetrical cornea. Dr. Waring said the OPD is also an autorefractor, and differs from other autorefractors because it works by a time-based retinoscopy principle, meaning that the diagnostic slit beam sweeps back and forth across the pupil to gather reliable refractive information with 1,440 measurement points. One unique feature is that the OPD displays the actual, spatially resolved optical error for the whole eye, as EyeWorld Monthly Pulse EyeWorld Monthly Pulse is a reader survey on trends and patterns for the practicing ophthalmologist. Each month we send an online survey covering different topics so our readers can see how they compare to our survey. If you would like to join the hundreds of physicians who take a minute a month to share their views, please send us an email and we will add your name. Email carly@eyeworld.org and put EW Pulse in the subject line—that's all it takes. Poll size: 189 August 2014 Keratorefractive surgery The creation of the refractive lenticule, which is then removed through a small incision for the SMILE procedure Source: D. Rex Hamilton, MD continued on page 44

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