Eyeworld

49 EW RESIDENTS November 2016 OPD-Scan Placido disc topogra- pher (Nidek, Gamagori, Japan) and ultrasound pachymetry, and did not include Scheimpflug imaging or Belin-Ambrosio ectasia testing. All treatments for transPRK and fem- toLASIK were performed with the same SCHWIND ORK-CAM plan- ning module (SCHWIND eye-tech- solutions, Kleinostheim, Germany), further reducing bias in outcomes. Treatment protocols were similar be- tween the two groups, correcting for manifest refraction. The main differ- ences were the extra wetting of the corneal epithelium with a balanced salt solution-soaked sponge for even wetting of the corneal surface and use of 0.02% mitomycin-C for 30 seconds in the transPRK group. Postoperatively, the transPRK group received topical corticosteroids only after epithelial closure and was treated with fluorometholone taper over a 9-week period, while the femtoLASIK group was tapered off of steroids over a 2-week period. The relatively hyperopic outcomes in the transPRK group (0.11±0.56 D) versus femtoLASIK (–0.09±0.46 D) could possibly be explained by a longer course of steroids inducing less my- opic regression. Better vision at the day 7 postoperative visit would be expected in the femtoLASIK group due to faster healing time. The study included only patients achieving 1-year follow-up, which is appro- priate, and presented excellent and stable refractive outcomes. There was a slightly better visual outcome in the transPRK group, possibly due to the slight overcorrection, which was statistically significant. One important limitation of the statistical methods used in the study is that the inter-group comparisons did not account for within-patient correlation. This is important as more than half of cases were bilat- eral. Since all of the transPRK eyes were bilateral, taking one eye from a bilateral case to analyze, although alleviating the issue of within-pa- tient correlation, would decrease the sample size by 50% for this group. The authors performed a large number of comparisons using t-tests and Chi-square tests, thus inflating the chance of false positive findings. Procedures for multiple compari- sons such as Bonferroni or Dunnett should be considered at least for comparisons of primary interest. Given that the data is longitudinal, analyses based on mixed models will generally be more powerful than using many t-tests. Other important demographic and/or clinical factors (e.g., corneal thickness, keratome- try, astigmatism, etc.) may need to be adjusted (if significant) as well. Additionally, because the procedures were performed by 11 different sur- geons, it may be helpful to perform the subgroup analysis, stratified by surgeon, in order to examine the potential bias in the final results. In summary, this study suggests similar refractive outcomes between transPRK and femtoLASIK. However, the study did not quantify post- operative pain, dry eye symptoms, patient satisfaction, or willingness to repeat the procedure, all of which are important when comparing procedures of different pain levels, corneal penetration, and recovery times. It would also be interesting to perform age-stratified subgroup analysis to see if there is a differ- ence in outcomes between younger and older patients as there was a wide age range among the includ- ed patients. While the sample size was sufficient to measure refractive outcomes, a much larger sample size would be necessary to evalu- ate the complication rate since the incidence of corneal haze and flap dislocation has decreased in recent years with improved surgical tech- nique. The cost differential between the two procedures will also likely be an important factor to consider in the future. A large prospective study comparing transPRK, femtoLASIK, and SMILE with broader outcome metrics is desired to elucidate whether one procedure is superior to the others. EW References 1. Chen LY, et al. Comparison of femtosecond and excimer laser platforms available for cor- neal refractive surgery. Curr Opin Ophthalmol. 2016;27:316–322. 2. Haq Z, et al. Infections after refractive surgery. Curr Opin Ophthalmol. 2016;27: 367–372. 3. dos Santos AM, et al. Femtosecond la- ser-assisted LASIK flap complications. J Refract Surg. 2016;32:52–59. 4. Li SM, et al. Laser-assisted subepithelial keratectomy (LASEK) versus photorefrac- tive keratectomy (PRK) for correction of myopia. Cochrane Database Syst Rev. 2016;2:CD009799. Editors' note: The faculty mentors/ reviewers were David Jackson, MD, clinical associate professor, and R. Michael Siatkowski, MD, residency program director, Dean McGee Eye Institute. Contact information Jackson: David-Jackson@dmei.org Siatkowski: RMichael-Siatkowski@dmei.org stephensinst.com | +1.859.259.4924 Stephens Instruments | 2500 Sandersville Rd | Lexington KY 40511 USA Toll Free ( USA ) 800.354.7848 | Fax 859.259.4926 | info@stephensinst.com © 2016 Stephens Instruments. All rights reserved. LIFETIME WARRANTY 3 0 D A Y N O - R I S K T R I A L ISO 9001 ISO 13485 MICROSURE™ FEMTO TORIC S9-2070 S5-1535 ST5-7035 Stephens offers over 1,500 high-grade surgical stainless steel and titanium instruments, every one backed by a 30 day no-risk trial and lifetime warranty. You could pay more for your instruments, but why? Choose Stephens, trusted for over 40 years, and invest the savings in your practice—and your patients. The smart choice.

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