OCT 2013

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

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88 EW REFRACTIVE SURGERY October 2013 When newer is better: Comparing the IntraLase laser systems by Edward E. Manche, MD O ne of the characteristics that makes ophthalmology so exciting to practice is the relative speed with which new technologies are introduced. Compared to other areas of medicine, trials and approvals happen faster and new ideas make it to market frequently. However, it can sometimes be difficult to discern if the latest device brings a true advantage or is just another capital investment. I am generally an early adopter of new technologies, and such was the case with the iFS laser system, the 150 kHz laser built on the IntraLase platform (Abbott Medical Optics, AMO, Santa Ana, Calif.). The iFS laser has some obvious advantages over the previous generation IntraLase FS 60 laser system (FS Uncorrected visual acuity at one week postop Patient preference postop Source (all): Edward E. Manche, MD 60). First, the repetition speed of 150 kHz versus 60 kHz makes the new laser 2.5 times faster than the previous generation. A faster procedure indicates less time with the suction device on the eye and a generally more comfortable procedure for the patient. In addition, an inverted sidecut flap, possible only with the iFS laser, has been shown to have better wound stability1 and induce fewer symptoms of dry eye.2 Even though I had already made the investment, I felt it worthy to do a direct comparison of the iFS laser and the previous generation, the IntraLase FS 60 laser system. To conduct a true comparison of the lasers, I operated on 61 patients, one eye with the iFS laser and the fellow eye with the FS 60, with the eyes randomized by ocular dominance. All eyes had a programmed flap thickness of 105 microns, with a 9.0 mm superior hinge. With the iFS laser, I performed a 130 degree inverted sidecut angle and with the FS 60, a 70 degree beveled sidecut angle. All eyes underwent wavefront-guided ablation with the CustomVue S4 excimer laser (AMO). One of the most obvious differences between the lasers is the speed at which they are able to create the flap. With the iFS laser, the flap can be created in approximately 12 seconds, whereas with the FS 60 it takes about 30 seconds. Immediately after creating the flap in both eyes, we paused the surgery and asked the patients if they had a preference between the two flap procedures, and 53% reported that they preferred the iFS laser procedure, compared to 26% that preferred the FS 60 laser procedure and 21% that had no preference. This difference in patient preference presented the first clinical advantage to the iFS laser. The second significant clinical difference came with the speed of visual recovery. At postoperative week one, 81% of eyes treated with the iFS laser had uncorrected visual acuity (UCVA) >20/16, compared to 69% in the FS 60 group (p=0.0497). By six months postop, the number of FS 60 eyes with UCVA >20/16 had increased to be approximately equal to the iFS laser group. In other words, both groups got to the same endpoint, but visual recovery was faster with the iFS laser. Higher-order aberrations such as coma, trefoil, and spherical aberration were analyzed, and while there was less of each in the iFS 150 group, the difference wasn't enough to reach statistical significance. Predictability also showed a slight advantage for the iFS 150 in the early postoperative period with slightly more patients +0.25 D of emmetropia (77% vs. 61%), but this evened out by six months. There was no significant difference in 5% and 25% contrast acuity scores between the two groups, and the safety profiles were excellent for both. For flap creation in a LASIK procedure, the iFS laser is my go-to machine. Overall, I find that the iFS laser facilitates the amount of time in surgery for the physician, improving patient flow and reducing the amount of time patients have to sit in the operating room. It also provides better visual results in the early postoperative period, all aspects that contribute to happier patients. EW References 1. Knorz MC, Vossmerbaeumer U. Comparison of flap adhesion strength using the AMADEUS microkeratome and the IntraLase iFS femtosecond laser in rabbits. J Refract Surg. 2008;24(9):875-878. 2. Donnenfeld E. Preservation of corneal innervation with femtosecond laser inverted sidecut flaps. Invest Ophthalmol Vis Sci. 2010 51: E-Abstract 2855. Editors' note: Dr. Manche is director of cornea and refractive surgery, Stanford Eye Laser Center, and professor of ophthalmology, Stanford University School of Medicine, Stanford, Calif. Dr. Manche has financial interests with Best Doctors (Boston), Calhoun Vision (Pasadena, Calif.), Gerson Lehrman (New York), Krypton Vision (Fremont, Calif.), Refresh Innovations (Stanford, Calif.), and Seros Medical (Palo Alto, Calif). Contact information Manche: edward.manche@stanford.edu

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