EyeWorld Asia-Pacific March 2011 Issue

18 March 2011 EW REFRACTIVE Microkeratome flaps—similar outcomes to femto flaps? by Michelle Dalton EyeWorld Contributing Editor Separate clinical studies found the two flap-creation techniques similar T wo peer-reviewed articles have argued microkeratome- created flaps are not inferior to femtosecond laser-created flaps, and that thin-flap LASIK flaps can be made safely and efficaciously with a single-use microkeratome. In the latter case, however, the Moria One Use-Plus (Moria, Antony, France) could not realize a fully planar-shaped flap, although it was able to create a thinner flap than the single-use M2 (Moria). 1 In a head-to-head comparison between flaps created with the IntraLase 15 kHz (Abbott Medical Optics, Santa Ana, Calif., USA) and the Hansatome microkeratome (Bausch & Lomb, Rochester, NY, USA), Ramón Calvo and colleagues at the Mayo Clinic, Rochester, Minn., USA, determined there were no differences in corneal total higher-order aberrations (HOAs), spherical aberrations, coma, or trefoil between the two groups (n=21, with eyes being randomized based on ocular dominance). 2 While this seems to contradict some published studies that indicate a clear advantage for the femtosecond laser, several of those studies compared thin-flap LASIK with the IntraLase to full-thickness flap LASIK made with a standard microkeratome. In the Mayo Clinic study, neither uncorrected nor best corrected visual acuity was statistically significantly different at any follow-up time point between the two flap styles. Femtosecond flaps “have a planar configuration; flap thickness is uniform, in contrast to a flap created by a microkeratome, in which the center of the flap is thinner than in the periphery,” the Mayo Clinic study authors wrote. At one year, only four eyes of two patients required retreatment for mild undercorrection. No differences in HOAs were found in either the 4- or 6-mm pupil diameters; total HOAs increased in the 4-mm LASIK eyes after one month and stayed elevated through the 36-month follow- up. The IntraLase 4-mm eyes had no differences between pre- and post-op HOAs. In the 6-mm pupils, both the microkeratome and the IntraLase increased HOAs after one month, and they remained elevated throughout the study. The authors noted that the differences between pre- and post-op HOAs were not statistically significantly different between the two pupil diameters. In the study between the microkeratomes, Hui-Jin Chen, MD, and colleagues performed bilateral LASIK on 68 patients, 41 with the One Use-Plus microkeratome and 27 with the M2. Central corneal thickness was “dramatically thinner” in the One Use-Plus group; in both groups the right eyes were slightly thicker than the left. The One Use-Plus “did not show a markedly better uniformity than the M2 ,” but the authors noted the variation was mainly observed in the periphery. Thin-flap LASIK has long been touted as providing the best of conventional LASIK and surface ablation. Using a femtosecond laser to create the flap allows surgeons to make a geometrically precise LASIK flap, complete with uniform thickness across the periphery and center; supposed advantages over the microkeratome include fewer induced HOAs. Numerous studies in the literature as well as anecdotal stories confirm the safety of the femtosecond laser, as well as its efficacy. Surgeons often mention the ease-of-use of a femtosecond laser as one of its main attributes. Conversely, the microkeratome blades have not been without their own controversies, including the possibility of “rough” epithelium or uneven flap creation. The One Use-Plus is “very light, and easy to center and get suction”, said Jay Novetsky, MD, Vision Institute of Michigan, Sterling Heights, Mich., USA. He added that the nasal flaps are “pristine and thin with intact smooth epithelium, and there are no problems with striae to date”. Jacqueline Griffiths, MD, NewView Laser Eye, Reston, Va., USA, uses both the Moria CB and the One Use-Plus, and recommends any surgeon who might run into an issue with the CB hitting the speculum to “twist the ring in the opposite direction gently.” Gary Chung, MD, Evergreen Eye Center, Federal Way, Wash., USA, has used both as well but prefers the linear pass of the One Use-Plus. He connects the microkeratome to the suction ring and places the entire apparatus within the confines of the lids/ speculum to obtain suction. “Once suction is obtained, the pass can be performed immediately. This minimizes the time the eye is under vacuum, and you can be confident that nothing will obstruct the pass of the microkeratome,” he said. Numerous refractive surgeons use both femtosecond and microkeratome technologies, Dr. Griffiths said. “The bottom line is that the microkeratome technology has only gotten better with time,” she said. “It’s proven, reproducible, and achieves the excellent results the patient is looking for.” When a good flap is created, “it is a really good thin flap of about 100 microns,” said Gary Wortz, MD, Lebanon, Ky., USA. “Post-op day 1 vision is almost always 20/15 [6/4.5].” Those anecdotal experiences with the One Use-Plus supported the findings of the Mayo Clinic as well (even though the latter used a different microkeratome). They found no differences in visual outcomes between the two groups after three years and no real advantage with one flap technique over the other. Furthermore, in the Mayo study, intended flap thicknesses were different between the two groups, but achieved flap thicknesses were not statistically significantly different between the two groups. In Dr. Chen’s study, the authors note the mechanical microkeratome is the most commonly used device for LASIK flap creation in China; this may explain why femtosecond lasers were excluded from the study. In the early post-op period, the outcomes with the microkeratomes were comparable with each other. Dr. Chen did add that longer- term effects on the post-op HOAs, keratectasia, and refractive regression need additional study. “Currently in China, the One Use-Plus microkeratome may be an alternative to a femtosecond laser to perform thin-flap LASIK,” the authors concluded. “I believe both technologies are excellent devices. Both have proven track records. But I also believe that both have equal risks—just different risks,” Dr. Griffiths said. EW References 1. Chen H-J, Zia Y-J, Zhong Y-Y, et al. Anterior segment optical coherence tomography measurement of flap thickness after myopic LASIK using the Moria One Use-Plus microkeratome. J Refract Surg. 2010;26(6):403-410. 2. Calvo R, McLaren JW, Hodge DO, et al. Corneal aberrations and visual acuity after laser in situ keratomileusis: Femtosecond laser versus mechanical microkeratome. Am J Ophthlamol. 2010;149(5): 785-793. Editors’ note: None of the physicians interviewed have a direct financial interest in their comments. The Chen et al. study authors reported no commercial or proprietary interest in the material presented. The Mayo group reported funding/support from the National Institutes of Health and an unrestricted educational grant from Research to Prevent Blindness. Contact information Chung: 206-212-2100, gwchung@gmail.com Griffiths: 703-834-9777, jgriffiths@newviewlaser.com Novetsky: 586-254-1770 Wortz: 270-692-0047, 2020md@gmail.com Cornea marked for flap creation with microkeratome Source: Moria