EyeWorld Asia-Pacific September 2016 Issue

September 2016 26 EWAP FEATURE Views from Asia-Pacific Cordelia CHAN, MD Consultant Eye Surgeon, Eye Surgeons @ Novena, Mount Elizabeth Novena Specialist Centre, Singapore Visiting Senior Consultant, Singapore National Eye Centre, Singapore 11 Third Hospital Avenue, Singapore 168751 P atients and refractive surgeons around the world have enjoyed over two decades of success with LASIK for the correction of myopia and astigmatism. More recently, small incision lenticule extraction (SMILE) has begun gaining popularity, with many surgeons offering the procedure to their patients. Some surgeons have begun to advocate SMILE over LASIK, while there are others who have yet to adopt SMILE, and are quietly procrastinating on the sidelines. I have been performing SMILE since 2012 and have had good results with the procedure. It is technically more demanding than LASIK, with a steeper learning curve for the intricate process of lenticule dissection and extraction. However, with experience, proper instrumentation and good technique, the surgery can be performed quickly with minimal intraoperative complications. So how good is SMILE? Is SMILE better than Femto-LASIK? When comparing the two procedures, the following aspects need to be considered: visual outcomes, induction of dry eye, biomechanics, visual recovery and regression. When evaluating visual outcomes, studies have shown similar efficacy, predictability and safety for LASIK and SMILE. In relation to dry eye, there is less decrease in cornea sensitivity and innervation with SMILE up to the first 3 months, indicating less dry eye with SMILE in the early postoperative period. In terms of biomechanics, reports tend to show more variability. When considering the effect of each procedure on the tangential, cohesive tensile and shear strengths of the cornea, SMILE has been found to be biomechanically stronger than LASIK. However, studies using the ocular response analyzer (ORA) have shown variable results when the two procedures are compared. With the recent publication of cases of ectasia occurring after SMILE even in eyes with normal topography, there is now evidence that SMILE can weaken the cornea biomechanically. The same stringent topographic and pachymetric criteria applied to LASIK should therefore also apply to SMILE. Perhaps the most relevant clinical difference between SMILE and LASIK is the rate of recovery of vision afforded by the two procedures. There are published studies documenting a delay in visual recovery after SMILE compared to LASIK. This delay is more pronounced at postoperative day 1 and is less obvious after 1 week, with vision comparable in both procedures eventually after 1 to 3 months. Visual recovery and visual outcomes after SMILE have also been observed to be dependent on the femtosecond laser unit used to perform the procedure, with surgeons anecdotally reporting variable rates of recovery and outcomes with different units used. An advantage SMILE may have over LASIK is in the area of regression. In LASIK, regression especially in young patients and higher treatments has been documented over time in some cases. Early studies seem to suggest that there may be less such regression with SMILE. LASIK has enjoyed tremendous success, but the technology is reaching a plateau in its development. I believe that SMILE is a good procedure, and the concept of lenticule creation, dissection and extraction is an excellent one, and should be the focus of work on future corneal-based refractive surgery. However, with its current technology, SMILE will not surpass LASIK unless the problem of delayed visual recovery is addressed. With the existing evidence, SMILE should therefore not be marketed as better than LASIK, but instead as a good alternative to LASIK which carefully selected patients can benefit from. References 1. Lee JK, Chuck RS, Park CY. Femtosecond laser refractive surgery: small-incision lenticule extraction vs femtosecond laser-assisted LASIK. Curr Opin Ophthalmol . 2015;26:260-4. 2. He M, Huang W, Zhong X. Central corneal sensitivity after small incision lenticule extraction versus femtosecond laser-assisted LASIK for myopia: a meta-analysis of comparative studies. BMC Ophthalmology . 2015;15:141. 3. Reinstein DZ, Archer TJ, Gobbe M. Small incision lenticule extraction (SMILE) history, fundamentals of a new refractive surgery technique and clinical outcomes. Eye Vis (Lond) . 2014;1:3. 4. El-Massry AA, Goweida MB, Shama Ael-S, et al. Contralateral eye comparison between femtosecond small incision intrastromal lenticule extraction at depth of 100 and 160 microns. Cornea . 2015;34(10):1272–5. 5. Sachdev G, Sachdev MS, Sachdev R, et al. Unilateral corneal ectasia following small-incision lenticule extraction. J Cataract Refractive Surg . 2015;41:2014-8. 6. Agca A, Ozgurhan EB, Yildirim Y, et al. Corneal backscatter analysis by in vivo confocal microscopy: fellow eye comparison of small incision lenticule extraction and femtosecond laser-assisted LASIK. J Ophthalmic . 2014;2014:265012. Editors’ note: Dr. Chan is a consultant for Alcon (Fort Worth, Texas). SMILE - from page 25