EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
Issue link: https://digital.eyeworld.org/i/76185
32 32 EW REFRACTIVE SURGERY July 2012 Faster treatments are possible via high-speed pupil tracking by Sonia H. Yoo, M.D. Faster ablation and tracking eases patient discomfort A dvanced laser systems can lead to more predictable outcomes, lower retreat- ment rates, better visual outcomes, and an overall increase in patient satisfaction. These same systems provide faster overall time in flap creation and ablation patterns, which reduces patient discomfort and potential undesirable outcomes. Currently, three excimer laser systems offer high-speed flap cre- ation and high-speed tracking. These include the WaveLight Allegretto Wave Eye-Q laser system (Alcon, Fort Worth, Texas), the VISX STAR S4/IR laser system (Abbott Medical Optics, AMO, Santa Ana, Calif.), and the Zeiss MEL-80 laser system (Carl Zeiss Meditec, Dublin, Calif.). I consider myself fortunate to have all three systems in my refractive surgery center at Bascom Palmer. The need for speed At first glance, these advanced lasers are similar—each has its own propri- etary version of wavefront or wave- front-optimized treatments; the Allegretto, VISX, and Zeiss are ap- proved for the treatment of myopia, hyperopia, and mixed astigmatism. The Zeiss offers both pupil and scle- ral tracking, while the Allegretto and VISX offer pupil tracking only (see Tables 1 and 2). The speed of pupil tracking is faster with the Allegretto at 400 Hz, compared to the Zeiss (250 Hz) and the VISX (60 Hz). The Allegretto and Zeiss both have laser speeds equal to the pupil trackers, while the VISX has a variable laser speed between 6-20 Hz. This translates to a 2.5 sec/ diopter treatment time for myopes in the Allegretto, a 5.0 sec/diopter treatment time for myopes in the Zeiss, and an 8.0 sec/diopter treat- ment time for myopes in the VISX. For hyperopes, the differences are even greater. The Allegretto needs 5.0 sec/diopter for hyperopes, the Zeiss needs 8.0 sec/diopter for hyperopes, and the VISX needs 20 sec/diopter for hyperopes. Patients are understandably nervous on the day of surgery. Once they're on the table, we ask them to fixate on a rather bright LED light, and we cannot allow them to blink. What may seem like only a few sec- onds to a surgeon may seem inter- minable to a patient. In the case of LASIK, the surgeon also has lifted the flap; the patient's vision is al- ready blurry and the urge to blink increases once the flap is lifted. Tim- ing, patient satisfaction, and com- fort become crucial at this point. For patients with smaller correc- tions, the difference in table time is small but still relevant. For instance, in a 1.00 D myope, the patient has to fixate almost three times as long if we're using the VISX as when we use the Allegretto. But as we all know, most of our patients have well over 1.00 D of needed correction, regardless of myopia or hyperopia. Imagine patients with +3.00 D; they're already blurry from the hy- peropia when we ask them to fixate, and now we're asking them to do so for 60 seconds under the VISX. A faster treatment time can be achieved with the Allegretto (15 sec- onds). The differences grow expo- nentially the higher the treatment. Anecdotally, a number of my patients has said fear is the primary reason for not seeking surgical treat- ment earlier. When the speed of the treatment is short, these same pa- tients tell me if they had realized how simple it was, they would have sought treatment earlier. Technical advantages Aside from increased patient com- fort, quicker ablation times also mean the surgeon has better control over multiple variables, such as stro- mal surface hydration (which in turn leads to more predictable out- comes), less potential for eye move- ment, and overall improved patient satisfaction. Faster flying spots are equally advantageous for the surgeon. In order for the laser to be placed effec- tively, the pupil tracker has to be as fast as the laser. Today's trackers are much better at keeping up with the subtle natural eye movements than earlier versions. This, too, helps surgeons ensure the lasers are targeting the exact spot desired. Central islands are uncommon with the flying spot lasers since the abla- tion spot is cooled and the plume dissipates before the next spot is laid down in the same location. With today's faster lasers, sur- geons will have to ensure the spot they've hit cools before the next spot gets laid on top. Otherwise sur- geons are risking non-uniform abla- tions. That could potentially lead to a slightly increased risk of haze if surgeons don't let the heat dissipate properly. That was a concern when the faster lasers started entering the market. In our center, however, we haven't noticed any difference in the rates of haze between the earlier lasers and the current offerings. Study results At Bascom Palmer, we conducted an internal study on the average surgi- cal time between the Allegretto/ FS200 and the VISX/IntraLase. In both systems, we were using the femtosecond lasers for the flap and ablation. The Allegretto has a Gaussian beam profile, the VISX a flat top. As might be expected, the VISX has a variable spot size (com- plementing the variable laser) of between 0.65-5.0 mm; the Allegretto has a fixed 0.95 mm spot size. All patients were operated on by me, and they were sequential patients operated on in different weeks. At baseline, the mean manifest spherical equivalent of the 32 eyes that underwent treatment with the VISX was –2.80 D (range +3.63 D to –7.12 D); the mean manifest spheri- cal equivalent of the 23 eyes that underwent treatment with the Allegretto was –2.77 D (range +2.38 D to –6.50 D). With the VISX, mean time from flap lift to start of laser was 38.6 sec, and the mean time of laser ablation was 50.1 sec, for a total mean time of 88.7 sec of treatment. In the Allegretto, mean time from flap lift to start of laser was 26.7 sec, and the mean time of laser ablation was 9.8 sec, for a total mean time of 36.5 sec of treatment. Advanced laser systems provide faster overall time in both flap cre- ation and ablation pattern. Factor in continued on page 33 Source (all): Sonia H. Yoo, M.D.