Refractive and Keratometric Stability in High Myopic LASIK With High-Frequency Femtosecond and Excimer Lasers

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1 ORIGINAL ARTICLE Refractive and Keratometric Stability in High Myopic LASIK With High-Frequency Femtosecond and Excimer Lasers Anastasios John Kanellopoulos, MD; George Asimellis, PhD ABSTRACT PURPOSE: To evaluate safety, effi cacy, ergonomy, and refractive and keratometric stability in high myopia LASIK procedures using a novel femtosecond and excimer laser surgery platform. METHODS: One hundred sixteen eyes in consecutive cases of high myopic LASIK ( diopters [D]) with the Alcon-WaveLight FS200 femtosecond and EX500 excimer lasers (Alcon Laboratories, Fort Worth, TX) were evaluated preoperatively and postoperatively for the following parameters: refractive error, corrected distance visual acuity, uncorrected distance visual acuity, spherical equivalent correction, keratometry (with Placido topography and Scheimpfl ug tomography), and refractive astigmatism. Average follow-up time was 6.2 months (range: 3 to 12 months). RESULTS: Postoperative average refractive error was -0.37, -0.43, and D for the 3-, 6-, and 12-month period, compared to ± 1.55 D preoperatively. At 3, 6, and 12 months postoperatively 94%, 96.3%, and 100% of eyes, respectively, were within 1.0 D defocus equivalent. Postoperative refractive astigmatism was -0.21, -0.21, D for the 3-, 6-, and 12-month period compared to ± 1.91 D preoperatively. The proportion of eyes with postoperative astigmatism within 0.25 D was 85.3%, 81.5%, and 100%, for the 3-, 6-, and 12-month visit, respectively. Keratometric stability was within 0.22 D after the 12-month visit. There was no epithelial ingrowth or diffuse lamellar keratitis in any case. CONCLUSIONS: Clinical outcomes with this technique and technology appear to be promising in high level uncorrected visual rehabilitation of high myopia. There was small regression potential in the sample evaluated. [J Refract Surg. 20XX;XX(X):XX-XX.] B oth excimer and femtosecond laser platforms have evolved significantly over the past 10 years. Today s excimer lasers for refractive surgery have high pulse repetition (more than 400 Hz), 1,2 operate with scanning spot, 3 and can provide customized ablation, including aspheric ablation profiles 4 and wavefront-guided 5,6 or topography-guided 7,8 treatments. These improvements have further advanced the applications of the LASIK procedure 9,10 in correcting not just the spherocylindrical refractive error, but also the higherorder aberrations. 1,11,12 The Alcon-WaveLight EX500 excimer laser and the FS200 femtosecond laser 13 constitute the Alcon-WaveLight Refractive Suite (Alcon Laboratories, Fort Worth, TX). The Refractive Suite operates on its own Ethernet network and allows the importation of diagnostic data from several networked screening devices (including Vario Placido topography, Oculyzer II Scheimpflug tomography, Tscherning wavefront analysis, and the OB820 interferometric biometry system 14 ) into the planning software tools of both lasers. Specifically for high myopia (refractive error diopters [D] in the least minus meridian), although LASIK provides reliable outcomes, 15 there are reports indicating that significant regression develops in the long term. 16,17 This matter has been discussed in the past 18,19 and gained new interest with the advent of femtosecond laser-assisted LASIK. 20 Due to the large ablation depths required for the correction of high refractive error, obvious potential limitations of high myopic LASIK are risk for reduced accuracy, higher risk of ectasia, and potential for increased postoperative spherical aberration. To allow for thicker residual stroma, a thinner flap is preferable. From Laservision.gr Institute, Athens, Greece (AJK); and New York University Medical School, New York, New York (AJK, GA). Submitted: November 29, 2012; Accepted: May 13, 2013 Dr. Kanellopoulos is a consultant to WaveLight. The remaining authors have no financial or proprietary interest in the materials presented herein. Correspondence: Anastasios John Kanellopoulos, MD, Laservision.gr Eye Institute, 17 Tsocha Street, Athens, Greece. ajk@brilliantvision.com Journal of Refractive Surgery Vol. xx, No. x, 201X 1

2 Parameter TABLE 1 Preoperative and Postoperative Parameters a Preoperative (n = 116 Eyes) 3 Months Postoperatively (n = 116 Eyes) 6 Months Postoperatively (n = 105 Eyes) 12 Months Postoperatively (n = 92 Eyes) Refractive error (D) ± ± ± ± 0.10 Refractive astigmatism (D) ± ± ± ± 0.04 D = diopters a Mean ± standard deviation. The purpose of this study was to evaluate the safety, efficacy, and ergonomy in high myopic LASIK using the FS200 femtosecond and EX500 excimer laser refractive surgery platform, including the long-term stability of the refractive and keratometric results. PATIENTS AND METHODS This retrospective interventional case series study received approval by the Ethics Committee of our institution and adhered to the tenets of the Declaration of Helsinki. Informed consent was obtained from each subject at the time of the intervention. The study was based on results obtained during scheduled preoperative and postoperative procedure patient visits. REFRACTIVE PROCEDURE The 58 patients evaluated in the study underwent uncomplicated primary bilateral LASIK by the same surgeon (AJK) on the same refractive surgery platform (FS200 femtosecond and EX500 excimer laser) between September 2009 and November To be considered for the study, the preoperative spherical equivalent was between and D and up to -5.0 D of cylinder refractive error. In all cases, the LASIK flap was planned for a 110-μm thickness and 8-mm diameter. All cases were treated with the enhanced wavefront-optimized version in the WaveLight procedure named F-CAT. This customized option allows for further asphericity reduction additional to the wavefront optimized standard option with this laser. We chose to adjust the desired postoperative Q value to -0.5 (the software allows for adjustment from 0 to -1, in 0.1-increments). All optical zones were 6.5 mm with a 1-mm transition zone regardless of preoperative pupillary measurements. Exclusion criteria were systemic or ocular diseases, eyes with history of corneal dystrophy or herpetic eye disease, topographic evidence of keratoconus (as evidenced by Placido topography), or warpage from contact lenses, corneal scarring, glaucoma, severe dry eye, and collagen vascular diseases. Postoperative clinical evaluations were conducted at 1 week, 3 and 6 months, and 1 year postoperatively. Average follow-up was 6.2 months. Of the initial 116 cases (eyes) included in the study, the number of cases (eyes) included in the subsequent follow-up visits was 116 at 3 months, 105 at 6 months, and 92 at 12 months. All eyes were evaluated preoperatively and postoperatively for the following parameters: manifest and cycloplegic refractive error, corrected distance visual acuity, and uncorrected distance visual acuity. The evaluation also included slit-lamp microscopy, tonometry, wavefront analysis (conducted via Tscherning aberrometry, Allegro Wavefront Analyzer I, Alcon-Wave- Light), contrast sensitivity (evaluated via CSV-1000 vision testing; Vector Vision, Greenville, OH), and keratometric evaluation (conducted with Placido topography and Scheimpflug imaging tomography). DATA ANALYSIS Data were processed by the web-based ophthalmic outcome analysis software application known as Internet-based refractive analysis (IBRA Ophthalmic Outcome Analysis System; Zubisoft GmbH, Oberhasli, Switzerland), 21 which facilitates internationally accepted presentation methods including the stability, predictability, and safety charts and is able to perform vector analysis for the course of a single patient or for group data. This study employs the summary results offered by the output of this software application. RESULTS Of the 116 patients, 66 (59.6%) were female and 50 (43.1%) were male. Mean age at the time of the operation was 28.7 ± 7.47 years (range: 17 to 51 years). The average flap diameter was measured with a digital image processing technique of the femtosecond laser intraoperative images 22 and was found to be 7.95 ± 0.05 mm in diameter, whereas the average flap thickness measured postoperatively (typically during the 3-month visit) via high-frequency ultrasound technique 23 was 107 ± 5.0 μm. The preoperative uncorrected distance visual acuity was 0.01 ± 0.08 (decimal) (20/200 Snellen), ranging from to Mean preoperative manifest spherical equivalent and cylinder are shown in Table 1. Figure 1 illustrates the postoperative spherical equivalent refraction within intervals of 0.50 D. Figure 2 displays the postoperative refractive astigmatism within in- 2 Copyright SLACK Incorporated

3 Figure 1. Spherical equivalent correction at the 3-, 6-, and 12-month postoperative visit, respectively. UDVA = uncorrected distance visual acuity; CDVA = corrected distance visual acuity Figure 2. Refractive astigmatism preoperatively and at 3-, 6-, and 12-month postoperative visits. Percentage of eyes (vertical axis) versus refractive astigmatism (diopters [D]) (horizontal axis). only real retina data from 169 laser spots projected onto the retina are imaged and analyzed. By design, this process does not image well in high myopia, or even after successful correction due to projection distortion. Nevertheless, all patients were evaluated at the 3- and 12-month visit with the above aberrometer. We were able to image 54 of the 116 eyes with mean aberrometric measurement of 0.38 ± 0.25 μm. UNCORRECTED VISUAL ACUITY OUTCOME AND STABILITY The uncorrected visual acuity (distance monocular) outcome and stability for the first 3 months (Figure 4) shows that 90.50% of the eyes had postoperative uncorrected visual acuity better than 1.0 (20/20), whereas 92.20% had better than 0.8 (20/25). Figure 4 also displays the preoperative corrected distance visual acuity for the same group of patients. Figure 3. Contrast sensitivity (average comparison between postoperative (average) and 3-month postoperative visit (average) on the CSV-100 Contrast Sensitivity Chart. tervals of 0.50 D. Average preoperative and postoperative contrast sensitivity results are illustrated in Figure 3. Tscherning aberrometry was attempted preoperatively and postoperatively in all cases. None of the cases was successfully measured preoperatively with the specific aberrometer due to inherent limitations of this architecture for high defocus such as the over -6 D in our sample. In the specific Tscherning aberrometry, Journal of Refractive Surgery Vol. xx, No. x, 201X EFFICACY OF CORRECTED VISUAL ACUITY As shown in Figure 5, the changes in corrected distance visual acuity at 3 months compared to preoperative corrected distance visual acuity and postoperative uncorrected distance visual acuity indicate that 30.4% of the eyes were unchanged, whereas 55.6% of the eyes gained one Snellen line and 12.2% gained two or more Snellen lines. Only 1.7% (2 eyes) lost one line. Even better results occurred at the 6- and 12-month visits, at which no eye had lost any Snellen line (also shown in Figure 5). REFRACTIVE STABILITY AND PREDICTABILITY The refractive stability is demonstrated by the spherical equivalent correction over the 12-month postoperative visit (Figure 6). Defocus equivalent results are presented in Figure 7. At the 3-, 6-, and 12-month visit, 94.0%, 96.3%, and 100% of eyes, respectively, were within 1.0 D defocus equivalent. 3

4 Figure 4. Postoperative uncorrected distance visual acuity (blue columns) at 3 months versus preoperative corrected distance visual acuity (orange line). Figure 5. Percentage of eyes with gain/loss in Snellen lines of corrected distance visual acuity, at the 3-, 6-, and 12-month visit, respectively. SE = spherical equivalent Figure 6. Stability of spherical equivalent, expressed in diopters (D) at the 3-, 6-, and 12-month visit, respectively. Predictability results are illustrated in Figure 8, where the achieved spherical equivalent versus attempted spherical equivalent (in diopters) at the 12-month visit is plotted. Of the 116 eyes at the 3-month visit, 92 were available for the 12-month visit; 3 eyes (3.2%) indicate slight overcorrection, 86 eyes (93.5%) are marked with green (indicating individual outcomes where the achieved spherical correction was within 0.5 D of the attempted correction), and 3 eyes (3.2%) indicate slight undercorrection. The data shown, corresponding to the 12-month visit, have a linearity of coefficient These results are in agreement with the spherical equivalent manifest refraction results (Figure 1), where spherical equivalent correction results recorded during the 3-, 6-, and 12-month postoperative follow-up visits are illustrated. KERATOMETRIC AND ASTIGMATIC CHANGES AND STABILITY The comparison between postoperative and preoperative refractive astigmatism is demonstrated by the percentage of eyes within 0.25 D of postoperative refractive astigmatism. Figure 2 presents the 3-, 6-, and Figure 7. Defocus equivalent results, at the 3-, 6-, and 12-month visit, respectively. 12-month refractive astigmatism. Astigmatism was within 0.5 D in 85.3% of the eyes at 3 months, 81.5% of the eyes at 6 months, and 100% of the eyes at 12 months postoperatively. The keratometric changes and stability are demonstrated by the K-flat and K-steep average values as followed during the 1-, 3-, 6-, and 12-month postoperative visits (Figure 9.) DISCUSSION In our study of 116 cases, the 1-year high myopic LASIK evaluation of the the WaveLight Refractive Suite shows impressive refractive outcome, predictability, and stability. Regarding efficacy, the refractive results expressed in terms of spherical equivalent refraction, in agreement with the defocus equivalent results, indicate that 83% and 93% of eyes were within 0.5 D at the 3- and 12-month visits, respectively (Figure 7). In terms of visual rehabilitation, 90.5% of the eyes achieved postoperative uncorrected distance visual acuity better than 1.00 (20/20) (Figure 4) and a significant percentage (53.5%) of the cases achieved better 4 Copyright SLACK Incorporated

5 AQ1Figure 8. Predictability of spherical equivalent correction, measured at the 12-month visit, showing achieved spherical equivalent (SE) (vertical axis, in D) versus attempted SE (horizontal axis, in D). Journal of Refractive Surgery Vol. xx, No. x, 201X Figure 9. Keratometric (K) readings at the 3-, 6-, and 12-month visit, respectively. than 1.25 (20/16). This compares to only 72.5% of the eyes having corrected distance visual acuity of 1.00 (20/20) preoperatively. In terms of gained or lost Snellen lines, only 1.7% (2 cases) had a loss in Snellen lines and most gained at least one line. These visual outcomes are satisfactory. The predictability of the outcome was extremely accurate. As shown in Figure 8, only 3 of the 116 eyes (3%) were overcorrected. Regarding the cylinder correction (Figure 2), 85.3%, 81.50%, and 100% of eyes had residual cylinder power less than 0.25 D at the 3-, 6-, and 12-month visits, respectively, compared to 81% of the eyes preoperatively. The stability of the outcome is evidenced by the strength of the spherical equivalent over the course of 12 months, as shown in Figures 1 and 6. The percentage of eyes achieving postoperative manifest refraction spherical equivalent in the to 0.00 D range of emmetropia was more than 87.5% after the 12-month visit (Figure 1). The cumulative percentage of eyes within ±1.0 D of emmetropia was 94% for 3 months, 96.3% for 6 months, and 100% for 12 months postoperatively. These results compare favorably to other studies, 24 in which the cumulative percentages were 98% within ±1.0 D 25 and 84.3% of eyes had a postoperative spherical equivalent within ±0.50 D of emmetropia. More importantly, no cases in our study had hyperopic manifest refraction spherical equivalent more than D. The slight positive slope in the keratometric readings, similar for both the flat and the steep meridian, as illustrated in Figure 9, might indicate a mild progressive corneal steepening. The recorded changes correspond to D for the flat meridian and D for the steep meridian. This is an indication that corneal stiffening might be required for all LASIK cases, in the form of cross-linking applied at the corneal stroma prior to repositioning of the flap. 26 The data clearly show a trend toward mild corneal steepening in the longer postoperative period, confirming our clinical observations of the potential need of a stabilizing adjunct procedure such as high fluence, short duration corneal cross-linking. We have introduced 27 and reported 28 using the employment of a high-fluence corneal crosslinking within the high myopic LASIK procedure as a possible means to achieve better long-term stability. A slight hyperopic shift of the total refractive error was observed comparing the 3- and 12-month postoperative results, which was on average from to D, or a change of 0.12 D. In correlation with the finding of slight steepening of K-readings over the same postoperative interval (+0.68 D), there is a slight contradiction that might be explained by the subjective nature of refractive error measurement (manifest refraction) versus an objective (Scheimpflug imaging) measurement of the keratometry. Perhaps further study of epithelial behavior and/or dry eye related to the LASIK flaps and a possible change in the biomechanical behavior of the cornea may explain this small discrepancy. Steepening of the K-reading (or regression of the myopic ablation) should manifest as myopic shift postoperatively and not a hyperopic shift. The long-term trend as noted in this study is toward a myopic shift. It is possible that the transient early hyperopic shift represents a build-in factor created by our nomogram for high myopia developed over 20 years of LASIK experience. The long-term steepening of most cases studied herein is significant in our opinion and needs to be reported. The long-term clinical results with the WaveLight Refractive Suite show impressive refractive outcome, predictability, and stability. Safety, efficacy, and ergonomy are of the highest level encountered. The networking of diagnostic devices increases ease and safety in using both the femtosecond and the excimer laser. 5

6 AUTHOR CONTRIBUTIONS Study concept and design (AJK); data collection (GA, AJK); analysis and interpretation of data (GA, AJK); drafting of the manuscript (GA, AJK); critical revision of the manuscript (AJK); administrative, technical, or material support (AJK); supervision (AJK) REFERENCES 1. Vega-Estrada A, Alió JL, Arba Mosquera S, Moreno LJ. Corneal higher order aberrations after LASIK for high myopia with a fast repetition rate excimer laser, optimized ablation profile, and femtosecond laser-assisted flap. J Refract Surg. 2012;28: Winkler von Mohrenfels C, Khoramnia R, Lohmann CP. Comparison of different excimer laser ablation frequencies (50, 200, and 500 Hz). Graefes Arch Clin Exp Ophthalmol. 2009;247: Iseli HP, Mrochen M, Hafezi F, Seller T. Clinical photoablation with a 500-Hz scanning spot excimer laser. J Refract Surg. 2004;20: de Ortueta D, Magnago T, Triefenbach N, Arba Mosquera S, Sauer U, Brunsmann U. 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