EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
Issue link: https://digital.eyeworld.org/i/82503
September 2012September 2012 EW REFRACTIVE SURGERY 69 Femtosecond flaps in the ditch by Maxine Lipner Senior EyeWorld Contributing Writer Which unexpected snags should be high on the radar? M ention the use of the femtosecond laser in conjunction with LASIK and many im- mediately think of the enhanced safety compared to the use of the mechanical microker- atome. While the bulk of literature supports this, that's not to say that the femtosecond doesn't have its own unique set of complications that may rarely occur, according to George O. Waring IV, M.D., director of refractive surgery, Storm Eye Insti- tute, assistant professor of ophthal- mology, Medical University of South Carolina, Charleston, and director, Magill Vision Center, Charleston. From suction loss to haze, practi- tioners may find themselves unex- pectedly mired in femtosecond hitches. Considering suction breaks Spurred by a paucity of literature on the relative complications with the femtosecond laser, Dr. Waring took a closer look at what happens when there is a suction break in one of these cases. "We wanted to get a sense of if a patient had a suction break and a recut, did it affect the outcome?" he said. In this retrospec- tive study published in the January issue of the Journal of Refractive Surgery, investigators considered all patients who had experienced a suction loss over the last 2 years at Japan's high-volume Shinagawa LASIK Center in Tokyo. Out of 232,000 femtosecond LASIK procedures performed here from 2006-2008, investigators found that there was suction loss during flap creation in just 71 eyes. Two main techniques were used depend- ing upon when this occurred. "If it occurred during the raster cut and [there was] a suction break, we would examine and make sure that there were no defects in the suction ring," Dr. Waring said. "In these cases, the same cone, the same pa- tient interface and the same suction ring were reapplied, with the same sized cut." One slight difference was the pocket setting would be turned off. "Our hypothesis was that if you make a very thin flap, potentially one of the causes of the haze is that you're breaking through Bowman's, and that's what's causing the haze," Dr. Yoo said. "We assume that nor- mally the epithelium is 50 microns but that there's some variability be- tween patients who may have a little thicker or thinner epithelium." She thinks that if you start making a flap that's thin in a patient who has a thicker epithelial layer than the average patient, you may start getting microscopic breakthrough of Bowman's layer and even of the basement membrane that can cause haze. To avoid haze such as this, it is recommended that practitioners usually limit femtosecond flap thickness to between 100 and 120 microns Source: Sonia H. Yoo, M.D. If the suction break occurred during the sidecut phase then the diameter would be decreased by 0.2 mm. Attention would go to initiat- ing the new sidecut. "There were some stromal irregularities observed after the flap lift, but these were out- side of the visual axis and would be reduced after you apply the excimer laser," Dr. Waring said. Loss of suction in the cases stud- ied didn't seem to appreciably affect outcomes. "We found that 97% of eyes that had suction loss were 20/20 or better," Dr. Waring said. "One hundred percent of eyes had corrected distance acuity of 20/20 or better or were within .5 D of plano." Practitioners were encouraged by the results. "It allowed us to real- ize that patients do fine even if you need to recut," Dr. Waring said. One of the potential factors that may have led to suction breaks in many of these cases, he thinks, was that despite the fact that the anatomy of the largely Asian popu- lation in Tokyo is not the same as elsewhere, only one sized suction ring is available with the IntraLase (Abbott Medical Optics, Santa Ana, Calif.). "This Asian population tends to have flatter keratometric readings and tighter interpalpebral fissures," Dr. Waring said. "As a result, it should be a signal for companies to think about anatomic variations and custom tailor or at least offer differ- ent sizes for different anatomic variation." Hazy outcomes Haze may be another issue with which femtosecond users may unex- pectedly need to contend. Practitioners at Bascom Palmer Eye Institute in Miami recently found themselves in such a situation in a case involving a 42-year-old man who had undergone what seemed to be uncomplicated LASIK, according to Sonia H. Yoo, M.D., associate professor of clinical ophthalmology, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine. They reported on this case in the January issue of the Journal of Refractive Surgery. The haze wasn't picked up ini- tially but was noted some time later. "He wasn't complaining of any light sensitivity or any post-operative problems in the early post-operative period," Dr. Yoo said. "When he came back at 4 months, however, he did note blurred vision and had some recurrent refractive error, and that was at the same time that we noticed significant interface haze." Investigators theorized that the haze was due to thin flaps. "When we measured the flaps they were calculated at much less than 100 microns," Dr. Yoo said. "The right one was 73 microns and the left was 81 microns." Using OCT, investiga- tors found some very focal breaks in the basement membrane of the epithelium as well as Bowman's layer that seemed to correspond with the areas of significant haze. To avoid this, Dr. Yoo recom- mended limiting flap thickness to between 100 and 120 microns in most cases. "In my practice now my default flap thickness is 120 microns," she said. "It's rare that I go under 100 microns because I think there is some variability in ep- ithelial thickness between patients." In this particular case, the patient fared well. Because he had residual refractive error there was some question as to how to best retreat this. "In this particular case you might consider using mito- mycin-C to try and prevent the haze from recurring after the retreat- ment," Dr. Yoo said. An alternative might be to do the retreatment as a surface ablation and remove the haze from the surface with the epithelium. Once again, Dr. Yoo recommended using mitomycin-C as an adjunctive agent to prevent haze recurrence. Overall, Dr. Yoo stressed caution in cases involving ultrathin flaps. "I would say to reserve ultrathin flaps for very specific cases because of the risk of haze," she said. EW Editors' note: The doctors mentioned have no financial interests related to this article. Contact information Waring: waringg@musc.edu Yoo: 305-326-6322, syoo@med.miami.edu