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For healthy eyes undergoing sub-Bowman's keratomileusis using advanced technology, outcomes for efficacy and safety, including effects on dry eye, are similarly excellent using either an 8- or 9-mm diameter flap.
Dr. Durrie provided some preliminary results and updates from his investigation. The study included 30 patients who met his usual screening criteria for wavefront-guided SBK. The patients had a mean age of 30 years with mean preoperative sphere and cylinder of –3.30 D and –0.49 D, respectively.
One eye was randomly assigned to have an 8-mm flap, and a 9-mm flap was made in the other eye. All flaps were created using a 150-kHz femtosecond laser (iFS IntraLase, Abbott Medical Optics) with a thickness of 100 æm, a 120° inverted side cut, and superior hinge. Wavefront-guided ablations were performed with an excimer laser (VISX S4 IR CustomVue, Abbott Medical Optics) with a target of plano.
Outcomes analyzed included uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), and evaluation of dry eye based on patient questionnaires, slit lamp exam, Schirmer test, and tear film breakup time (TFBUT). The results were excellent overall, and there were no statistically significant differences between study groups in any of those parameters at any follow-up visit. Iris capture rate was lower in eyes with the 8-mm flap than in the larger flap size group, 83% versus 93%, respectively, although Dr. Durrie noted factors other than flap size might account for the difference. Wavefront data are still being analyzed.
"Historically, LASIK has been performed using a 9-mm or larger flap based on the idea that matching the flap size to the ablation diameter would give the best vision results, and the majority of refractive surgeons continue using this technique," said Dr. Durrie, professor of ophthalmology, University of Kansas Medical Center, Kansas City, and president, Durrie Vision, Overland Park, KS. "However, there is a segment who believe a smaller flap may be better because it cuts less fibers and nerves and may therefore cause less dry eye.
"For the past 6 to 7 years, I have been using an 8.5-mm flap for all hyperopic and myopic corrections and have achieved excellent results, as documented by a number of clinical trials," he said.
The present study was designed to investigate rigorously the question of whether there are any specific advantages or disadvantages for bigger or smaller flaps, Dr. Durrie noted.
"It is a relatively small study with only 30 patients and I encourage others to repeat it," he said. "However, the results provide fairly solid evidence that should reassure surgeons performing SBK that they can be comfortable using smaller or larger flaps, whether they have a preference for one or the other or feel they should use a smaller flap in patients with smaller eyes."