EyeWorld Asia-Pacific June 2018 issue

June 2018 56 EWAP REFRACTIVE The thinking is that with SMILE you don’t need to respect the usual 250- to 300-micron stro- mal bed since you are not cutting the anterior stroma. “The SMILE surgeon says that 80 microns on top of the lenticule is not 80-mi- crons strength, it’s actually twice as strong because the anterior stroma is stronger than the posterior stro- ma,” Dr. Moshirfar said. “There- fore that 80 microns is double the thickness in terms of strength, so it’s 160 microns.” Instead of leaving a 300-micron residual stroma bed, some think that a 220-micron bed is sufficient. However, Dr. Moshirfar stressed that the patients who developed ectasia here were 20/20, were all young, had only between –2 and –6 D of myopia, and didn’t have a lot of astigmatism. “The cornea thickness among all of these eight eyes was more than 500,” he said, adding that all but two of them had a residual stromal bed above 300 microns. “Some people may say that they had funny looking topography and should not have had the surgery to begin with,” he said. “But we saw two eyes in this group that had normal thickness, a normal residual stromal bed above 300, normal topography, and they still developed ectasia.” Dr. Moshirfar asked what might be involved in developing a different metric specifically for SMILE. With LASIK flaps, one of the factors that is thought to be im- portant in corneal strength is that the incision goes approximately 11 clock hours around. “We are doing a vertical cut, which is around 23 mm,” he said. Meanwhile, a SMILE cap involves a superior incision, which is only about 5 mm, he continued, adding that this means with SMILE there should be about 70% less disruption in the anterior cornea. “The ratio is about 0.3,” Dr. Moshirfar said. “If you implement that ratio, maybe the percent tissue altered in these eyes shouldn’t be 40%.” Had practitioners used a modified PTA of 20%, they would have realized that six of the eight eyes here should not have under- gone the procedure. Others are looking into com- ing up with a new formula. Dr. Moshirfar hopes that those who are working on this take into ac- count the vertical incision that is made as part of the SMILE process. “We cannot assume that this tiny vertical incision that we’re making with SMILE is of no biomechani- cal impact,” he said, adding that if someone wants to come up with a metric, they need to keep the procedure’s vertical cut ratio to LASIK in mind in modifying the PTA factor. Overall, in ruling someone in or out for refractive surgery, abnor- mal topography is paramount, Dr. Moshirfar stressed. “If the cornea is otherwise normal but does have an asymmetric look to it, maybe we shouldn’t be doing refractive sur- geries on these eyes,” he said. EWAP Reference 1. Moshirfar M, et al. Ectasia following small-incision lenticule extraction (SMILE): a review of the literature. Clin Ophthalmol . 2017;11:1683–1688. Editors’ note: Dr. Moshirfar has no financial interests related to his com- ments. Contact information Moshirfar: cornea2020@icloud.com invasive and in-the-office, be some- thing that any cataract surgeon can do, and not require surgeons to train to become corneal refrac- tive surgeons. This is something we all want. When you survey ophthalmologists, they all want it.” When the Light Adjustable Lens is launched in the U.S., Dr. Lind- strom thinks that the first patients will be monovision patients. “A significant number of surgeons like to do monovision, which is a very demanding procedure as far as refractive outcome, particularly in the distance eye,” he said. “If a surgeon is going to do monovision, the distance eye needs to be dead on. There’s a little bit more forgive- ness in the near eye, but everyone who has done monovision or fit a monovision patient with contact lenses knows that patients can often appreciate a distance error of even 0.25 D. With contacts, it’s easy to adjust the power up and down a little to get it just the way the patient wants it. However, IOLs have been more challenging.” Dr. Lindstrom thinks the Light Adjustable Lens will allow surgeons to create a premium monovision channel. “We don’t have that today,” he said. “We have multi- focals (3% or 4% of the market), extended depth of focus IOLs (2% or 3%), and accommodating IOLs (maybe 1%). Approximately 25% of U.S. IOL patients are monovision patients. To hit the monovision just right, we would love to have an adjustable IOL where we can make the distance sight plano. In the non-dominant, near eye, we would over refract and maybe try a contact lens to decide the ideal pre- ferred near refraction. Then in the office, we could make the adjust- ment. That is a big opportunity.” Dr. Berdahl said that it is in- credibly promising technology. “It will allow all surgeons to achieve exquisite outcomes because we don’t have to rely on the estima- tions that we make preoperatively to get the right lens in place and estimate the effective lens posi- tion,” he said. “Once the lens is healed into position, we can fix any remaining residual refractive error based on the manifest refrac- tion. Things like surgically induced astigmatism, posterior corneal cur- vature, and effective lens position are all taken into account in the manifest refraction. Then we adjust the shape of the lens itself.” EWAP Editors’ note: Dr. Berdahl, Dr. Miller, and Mr. Freeman have financial interests with RxSight. Dr. Lindstrom has financial interests with Alcon (Fort Worth, Texas), Bausch + Lomb (Bridgewater, New Jersey), Carl Zeiss Meditec, Johnson & Johnson Vision (Santa Ana, California), and RxSight. Dr. Mamalis has no financial interests related to his comments. Contact information Berdahl: john.berdahl@ vancethompsonvision.com Freeman: rfreeman@rxsight.com Lindstrom: rllindstrom@mneye.com Mamalis: nick.mamalis@hsc.utah.edu Miller: kmiller@ucla.edu Light Adjustable – from page 50 When SMILE – from page 55