EyeWorld India June 2019 Issue

Óä EWAP JUNE 2019 S HANGHAI, China, April 2018—ZEISS (Jena, Ger- many) has reached yet another milestone in its over 170-year history. For the first time, the company has combined its cataract and refractive surgery user meetings, an acknowl- edgement of the blurring of the lines between the formerly distinct fields of anterior segment ophthal- mic surgery. Perhaps the most significant milestone reached by ZEISS in the last decade or so is its small-inci- sion lenticule extraction (SMILE) procedure that to date remains only possible with the precision optics of the VisuMax femtosecond laser. “SMILE is a fascinating pro- cedure,” said Tae-im Kim, MD , Seoul, South Korea. “It is the most advanced technology among the re- fractive procedures available today.” As benefits a procedure that occupies center stage in modern refractive surgery, the ZEISS user meeting focused significantly on this cutting-edge procedure. Dr. Kim discussed the quality of vision after SMILE, sharing her approach to meet patients’ expectations from the premium procedure, while a faculty of experts shared their own experiences and pearls during a Rap- id Fire “SMILE Learning” session. SMILE more: Quality of vision All surgeons who perform SMILE are satisfied with the refractive outcome it provides, Dr. Kim reported. How- ever, she wondered, what about the patient? Although Dr. Kim said that patients end up feeling good about their vision, they also pay more and in turn expect more from the procedure. To meet their expectations, Dr. Kim pays particular attention to minimizing decentration, a problem that can lead to corneal aberrations. Dr. Kim said that SMILE follows the Munnerlyn formula and is cen- tered on the corneal vertex. Optical zone centration is targeted to the coaxial corneal light reflex, also known as the first Purkinje image. SMILE is performed under mild suction and does not involve an eye tracking system. The align- ment of the refractive lenticule thus relies heavily on the patient’s cooperation. Decentrations have been reported in literature due to presumed difficulty in terms of patient cooperation and docking (Lee H, et al. Relationship Between Decentration and Induced Corneal Higher-Order Aberrations Following Small-Incision Lenticule Extraction Procedure. Invest Ophthalmol Vis Sci. 2018 May 1;59(6):2316-2324). To evaluate SMILE in her prac- tice, Dr. Kim first measured decen- tration during the procedure. She conducted a retrospective study on 360 eyes (360 patients) to investi- gate the amount of lenticule decen- tration following SMILE. Eyes were evaluated with use of the Keratron Scout (Optikon, Rome, Italy) Tan- gential Topography Difference Map. Dr. Kim and colleagues also inves- tigated the relationship between magnitudes of total decentration and induced corneal higher-order aberrations (HOAs). They defined the optical zone as the central zone up to the mid-peripheral power inflection point. Performing a piecewise linear regression of changes in root-mean- square (RMS) spherical aberration with total decentered displacement, the estimated breakpoint between induced RMS spherical aberration and total decentration is 0.355 mm. This measurement was used to dif- ferentiate Group I (total decentered displacement ) /= 0.335 mm) and Group II (total decentered displace- ment > 0.335 mm). Although decentration was higher in Group II, the mean postoperative uncorrected distance visual acuity (UDVA) (1.30 ± 0.20, range 0.60 to 1.50 vs. 1.27 ± 0.21, range 0.60 to 1.50 in Groups I and Shaping Tomorrow’s Vision: SMILE and SMILE Some More Supplement to EyeWorld Asia-Pacific June 2019 APACRS II, respectively; P =0.179) and post- operative mean refractive spherical equivalent (MRSE) (0.03 ± 0.25, range –1.50 to 1.07 vs. 0.03 ± 0.31, range –1.19 to 0.75, respectively; P = 0.419) were similar. However, more decentration induced larger total HOAs, coma, vertical coma, horizontal coma, and spherical aberration (Figure 1). Decentration of less than 0.335 mm could thus yield more satisfactory results with regard to aberrations, and accurate centration is crucial to reduce induction of corneal HOAs. Based on these findings, Dr. Kim initiated a second study to investigate lenticule decentration following SMILE via the subjective patient fixation method (Kang DSY, et al. Comparison of the Distri- bution of Lenticule Decentration Following SMILE by Subjective Patient Fixation or Triple Marking Centration. J Refract Surg . 2018 Jul 1;34(7):446-452) or triple-marking centration method and to compare induction of corneal HOAs between the two methods. Dr. Kim wanted to see how decentration can be minimized. For patients using the subjective patient fixation method (subjective centration group), alignment relied entirely on the patient's fixation to the target light. At the moment of contact between the individually calibrated curved contact glass and the cornea, the surgeon instructs the patient to look directly at the green light. A meniscus tear film ap- pears, at which point the patient is able to see the fixation target clearly because the vergence of the fixation beam is adjusted according to the individual eye's refraction. The triple-marking centration method is performed at the slit lamp. Using a very narrow hori- zontal slit beam for reference, the patient stares at the light, and markings are made at the 3 and 9 o’clock positions. The slit beam is then turned to the vertical position bisecting the coaxial corneal light reflex, and a marking is made at the 6 o’clock position. These markings are used as a reference to ensure correct centration while docking. Visual and refractive outcomes were comparable, although more eyes undergoing SMILE with the triple-marking method gained 2+ lines and achieved greater astig- matism correction (Figure 2). Eyes undergoing SMILE with subjective fixation were more decentered, with greater scatter around the corneal vertex. Moreover, SMILE with the triple-marking method significantly reduced total aberrations, coma, and spherical aberrations. Finally, Dr. Kim and her col- leagues conducted a retrospective case series of 89 eyes (45 SMILE with triple-centration eyes and 44 eyes with corneal wavefront-guided tran- sepithelial PRK [CWFG transPRK])— to investigate the clinical outcomes and vector analysis of myopia pa- tients with high astigmatism treated with the two procedures. Dr. Kim said that CWFG transPRK has been shown previously to perform well in correcting high astigmatism. The refractive outcomes were very similar, but Dr. Kim more frequently observed a 2+ line gain in transPRK; 20% of SMILE eyes versus 32% of CWFG transPRK eyes gained at least 1 line of visual acuity (Figure 3). Refractive astigmatism correc- tion was comparable between the two procedures, and both proce- dures induced very mild HOA. However, although more spherical aberrations were seen in CWFG transPRK, more coma was induced by SMILE. Based on these three studies, Dr. Kim concluded that having decentered distances of less than 0.335 mm could yield more satis- factory results with regard to visual outcome and total HOAs, coma, vertical coma, and spherical aber- ration. Performing SMILE with the triple-marking centration method can improve treatment centration, The news magazine of the Asia-Pacific Association of Cataract & Refractive Surgeons Figure 1. Subgroup analysis of corneal HOAs according to degree of total decentration Source: Tae-im Kim, MD