Comparison Between LASEK and LASIK for the Correction of Low Myopia

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1 Comparison Between LASEK and LASIK for the Correction of Low Myopia Laura de Benito-Llopis, MD; Miguel A. Teus, MD, PhD; Jose M. Sánchez-Pina, DO; Jose L. Hernández-Verdejo, DO ABSTRACT PURPOSE: To compare the refractive results of laser epithelial keratomileusis (LASEK) and laser in situ keratomileusis (LASIK) for the correction of low myopia. METHODS: A prospective, interventional, non-randomized, observer-masked study was performed of patients with myopia of 2.50 diopters (D) (cylinder 1.50 D) who had undergone either LASEK or LASIK. Refractive analysis was performed by a masked observer preoperatively and 1 day, 1 week, and 1 and 3 months postoperatively. RESULTS: Seventy-nine eyes that fulfi lled the inclusion criteria in each group were included in the study. No statistically signifi cant differences were noted in age, gender, or preoperative refractive error between groups. Postoperative uncorrected visual acuity (UCVA) was signifi cantly lower in LASEK eyes 1 and 7 days postoperatively (P=.0001). At 1 and 3 months postoperatively, no signifi cant differences were noted between the groups in UCVA (P=.07), but best spectacle-corrected visual acuity 3 months postoperatively was signifi cantly better in LASEK eyes (P=.01). The refractive error was similar in both groups (P=.3). CONCLUSIONS: Visual improvement after LASEK for low myopia is signifi cantly slower than after LASIK. Visual outcomes at 3 months postoperatively were similar with both techniques for the correction of low myopia. [J Refract Surg. 2007;23: ] L aser epithelial keratomileusis (LASEK) has become a popular technique in refractive surgery because of the absence of flap-related complications associated with laser in situ keratomileusis (LASIK), and because it allows treatment of thin corneas while achieving good outcomes in safety, efficacy, and predictability. Despite the disadvantages of LASEK, ie, slower visual recovery and higher postoperative discomfort than LASIK, this procedure has become the technique of choice in patients with thin corneal thickness, those who are keratoconus suspects, those at risk for trauma, and those with corneal surface problems such as dry eye, recurrent erosion syndrome, or basement membrane disease. 1 On the other hand, LASIK is a well-established, safe, and effective technique for correcting myopia. Nevertheless, cutting the cornea to create a flap may produce refractive changes 2,3 that, despite being slight, might be relevant in cases of low ametropia. Patients with low myopia who undergo refractive surgery can be demanding regarding the quality of vision after surgery, and these patients are often challenging for the surgeon. Because LASEK does not create a stromal flap, it could be a more precise procedure for treating low myopia. Several studies of LASEK-treated eyes show that the procedure is safe, effective, and predictable. 4-9 In studies that compared LASEK to photorefractive keratectomy (PRK), similar long-term results were seen with both techniques. However, we found few prospective studies that compared LASEK to LASIK, and in most of them 15,16 the ametropia ranged from 6.00 to diopters (D). Only one study 17 compared the results of both techniques for myopia 6.00 D. We did not find any studies that compared LASEK to LASIK From Vissum Corporación Oftalmológica (de Benito-Llopis, Teus, Sánchez- Pina, Hernández-Verdejo), Universidad de Alcalá (Teus), and Universidad Complutense (Hernández-Verdejo), Madrid, Spain. The authors have no proprietary interest in the materials presented herein. Correspondence: Laura de Benito-Llopis, MD, Vissum Corporación Oftalmológica, Madrid, Santa Hortensia 58, Madrid, Spain. lauradeb@hotmail.com Received: February 17, 2006 Accepted: June 27, 2006 Posted online: November 15, JRS0207LLOPIS.indd 139 1/30/2007 9:59:51 AM

2 for the treatment of low myopia ( 2.50 D). Therefore, we considered it of interest to determine whether LASEK is more precise than LASIK for the correction of low myopia. 140 PATIENTS AND METHODS PATIENT POPULATION A prospective, interventional, non-randomized observer-masked study was performed of consecutive patients (79 eyes in each group) who fulfilled the inclusion criteria: myopia 2.50 D and cylinder 1.50 D. Patients with unstable refraction, those who had undergone a previous ocular surgery (either refractive or other surgical procedures), keratoconus suspects, those with ocular disease, and those with systemic diseases that could alter the wound-healing process, such as diabetes and connective tissue disorders, were excluded. Minimal pachymetry to enter the study was 500 µm. The decision to perform either LASIK or LASEK was based on patient preferences after being fully informed about the advantages and disadvantages of both procedures. No statistically significant difference was noted between the groups in age, gender, or preoperative pachymetry. Patients in both groups were matched for the refractive error. All study patients underwent full ophthalmologic examinations preoperatively that included the determination of uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA) (using a Snellen chart [NIDEK auto chart projector CP 670 (NIDEK, Gamagori, Japan)] and manifest and cycloplegic refractions), slit-lamp microscopy, tonometry (CT- 80; Topcon, Tokyo, Japan), corneal pachymetry (DGH 5100 contact pachymeter; DGH Technology Inc, Exton, Pa), keratometry and corneal topography (Dicon CT200; Vismed Inc, San Diego, Calif), mesopic pupil measurement (Colvard pupillometer; Oasis, Glendora, Calif), and funduscopy. All surgeries were performed by the same surgeon (M.A.T.). SURGICAL TECHNIQUE Both procedures were performed using topical anesthesia (lidocaine 2%). In both cases, a povidone-iodine solution was used to disinfect the eye and a sterile surgical drape and a rigid eyelid speculum were positioned. During LASIK, the cornea was stained with two asymmetrical Gentian violet marks. The Moria M2 microkeratome (Moria SA, Antony, France) was used to create the flap, which then was raised with a spatula, the stromal bed dried with a sponge, and the eye tracker set in the center of the pupil. The Technolas 217C excimer laser (Bausch & Lomb Surgical, Claremont, Calif) was used to perform the ablation. The optical zone was determined by the mesopic pupil measurement. The stroma was washed and the flap gently put back in place with a cannula and aligned with the corneal marks. Antibiotic drops (ciprofloxacin 3%) and nonsteroidal anti-inflammatory drops (ketorolac trometamol 5%) were applied. During LASEK, the cornea was not marked. A 7-mm corneal semi-sharp marker (ASICO, Westmont, Ill) was placed on the cornea and centered on the pupil. A 20% alcohol solution (diluted in balanced salt solution [BSS]) was instilled inside the trephine and left for 40 seconds. A cellulose sponge was used to remove the alcohol and BSS copiously instilled to rinse the eye. The edges of the flap were dried with a sponge and the epithelial flap was peeled back with a crescent blade (Alcon Surgical, Orlando, Fla), leaving a hinge at the 12 o clock position. The stromal bed was dried with a sponge, the eye tracker was set in the center of the pupil, and the ablation performed with the same excimer laser as in the LASIK cases, using a PRK nomogram. The ablation zone was determined by the mesopic pupil measurement, as in LASIK. Once the ablation was completed, the stroma was washed with BSS and the epithelial flap was repositioned with the same cannula. A therapeutic soft contact lens (Acuvue; Johnson & Johnson Vision Care Inc, Jacksonville, Fla) was carefully placed on the eye and the same antibiotic and anti-inflammatory drops were applied as in LASIK. POSTOPERATIVE FOLLOW-UP The medications consisted of antibiotic (ciprofloxacin 3%) and steroid (dexamethasone alcohol 1%) drops four times daily after both procedures during the first week postoperatively. In patients who underwent LASIK, the drops were stopped after the first week; only artificial tears were continued thereafter. In the patients who underwent LASEK, steroid drops were tapered over the subsequent 2 months: three times daily the first month, twice daily for the next 15 days, and once daily for another 15 days and then stopped. The therapeutic contact lens was removed 1 week after surgery. Examinations were scheduled at 1 day, 1 week, and 1 and 3 months postoperatively. Two optometrists, masked to the preoperative refraction and surgery, performed the refractions at each postoperative visit. All patients were refracted in the same room with the same light adjusted to mesopic conditions. The endpoint in visual acuity was 1.5 Snellen visual acuity. STATISTICAL ANALYSIS The Statview Graphics (Abacus Concept Inc, Cupertino, Calif) was used for data analysis. Statisti- journalofrefractivesurgery.com JRS0207LLOPIS.indd 140 1/30/2007 9:59:55 AM

3 Figure 1. Postoperative uncorrected visual acuity (UCVA). Comparison between LASEK and LASIK. *Statistically significant difference. cal comparisons were done with the paired two-tailed Student t test and the chi-square test. Statistical significance was considered as P.05. Snellen visual acuity was converted to logmar for statistical analysis using a visual acuity conversion chart. RESULTS Mean patient age was years (range: 19 to 46 years) in the LASEK group and years (range: 20 to 66 years) in the LASIK group (P=.06). The mean preoperative spherical refraction values were D and D, respectively (P=.4) (range in both groups: 0 to 2.50 D). The mean preoperative cylinder values were D and D in the LASEK and LASIK groups, respectively (P=.9) (range in both groups: 0 to 1.50 D). The preoperative BSCVA levels were and , respectively (P=.3) (range in both groups: 0.95 to 1.25). The mesopic pupil measurement (and subsequently, the ablation zone) was mm in the LASEK group (range: 6 to 7 mm) and mm in the LASIK group (range: 5.5 to 7 mm) (P=.9). The postoperative UCVA was significantly lower in eyes treated with LASEK on postoperative days 1 and 7 (P=.0001) (Fig 1). At 1 and 3 months postoperatively, no significant differences were noted in UCVA between the two groups (P=.07). Three months postoperatively, the Snellen BSCVA levels were in the LASEK group and in the LASIK group (P=.01) (range in both groups: 0.95 to 1.25). The mean spherical refraction values at the same time point were D (range: 0 to 1.00 D) and D (range: 0.50 to 1.00 D) in the LASEK and LASIK groups, respectively (P=.2), and the mean cylinder values were D (range: 0 to 1.00 D) and D (range: 0 to 1.25 D), respectively (P=.4). The safety index (postoperative BSCVA/preoperative BSCVA) was in the LASEK group and in the LASIK group. This difference was statistically significant (P=.03). The efficacy index (postoperative UCVA/preoperative BSCVA) was in the LASEK group and in the LASIK group (P=.6) (Figs 2 and 3). The predictability is shown in Figures 4 and 5. Changes in BSCVA are shown in Figure 6. Given that all pre- and postoperative BSCVA levels remained between 1 and 1.25 on the Snellen chart, the loss of one line indicated a decrease in visual acuity from 1.25 to 1, and a gain of one line indicated an increase in visual acuity from 1 to No LASEK patients required enhancement, whereas three LASIK eyes underwent a retreatment procedure 3 months postoperatively (P=.1 using the chi-square contingency table). No intraoperative or postoperative flap complications occurred in the LASIK-treated eyes. In the group who underwent LASEK, no subepithelial haze higher than grade I was detected at any of the postoperative visits. DISCUSSION In the current study, the postoperative UCVA was significantly better after LASIK on days 1 and 7 postoperatively, but the difference was not significant 1 and 3 months postoperatively. The BSCVA 3 months after surgery was slightly but significantly better in LASEK eyes. Both procedures were safe, effective, and predictable for the treatment of low myopia; the safety index 141 JRS0207LLOPIS.indd 141 1/30/2007 9:59:55 AM

4 Figure 2. Cumulative uncorrected visual acuity (UCVA) in the LASEK group. Figure 3. Cumulative uncorrected visual acuity (UCVA) in the LASIK group. was slightly but significantly higher in LASEK, however, such minimal difference is not clinically relevant. When interpreting the visual acuity, attention must be drawn to the fact that on postoperative days 1 and 7 patients who underwent LASEK still had the bandage contact lens on, which could alter the values of visual acuity in two ways: it may either improve the visual acuity by diminishing irregular astigmatism, or it may worsen it because of the deposits on the lens. We could not compare our results to those of other 142 series, as, to the best of our knowledge, no studies have compared LASIK to LASEK to treat myopia 2.50 D. Gabler et al 18 performed LASEK retreatment in 10 eyes with a residual refractive error of 1.00 to 3.00 D after previous LASEK and reported that 100% of eyes were within 0.50 D of the intended correction. Kaya et al, 17 who compared the results of LASEK and LASIK for myopia 6.00 D, found no statistical differences between the techniques in UCVA, BSCVA, or refractive error at 1, 3, and 6 months postoperatively. journalofrefractivesurgery.com JRS0207LLOPIS.indd 142 1/30/2007 9:59:56 AM

5 Figure 4. Spherical equivalent refractive outcome. Figure 5. Defocus equivalent refractive outcome. Unfortunately, the authors do not state in their article whether the patients were matched for essential preoperative factors such as refractive error. This is why it is difficult to compare their results to ours. The ideal design of a study to detect differences between two different techniques is a prospective, controlled, randomized trial. The randomization of each patient to one or the other procedure avoids possible selection bias. In the current study, the differences between both techniques in terms of postoperative discomfort led to the impossibility of randomization. All patients were offered a choice between both procedures after being fully informed of the advantages and disadvantages of each one of them. We do not believe our study has a significant selection bias, because all patients included in this study were eligible for both 143 JRS0207LLOPIS.indd 143 1/30/2007 9:59:57 AM

6 Figure 6. Change in best spectacle-corrected visual acuity (BSCVA). One line of BSCVA was lost in 18 eyes after LASEK and 23 eyes after LASIK (P=.4). One line of BSCVA was gained in 5 eyes after LASEK and 3 eyes after LASIK (P=.5). techniques, they were consecutive and matched for the refractive error, and the groups were not statistically different in age or gender. Our follow-up schedule did not permit us to detect the exact moment when the UCVA became virtually the same between both groups. We did not collect a specific questionnaire to have comparable data in the visual discomfort after both techniques. Nevertheless, in our daily practice, LASEK patients are asked about their discomfort and they tend to have more glare and discomfort during the first postoperative week than LASIK patients. The discomfort only lasts for the first postoperative days, until the epithelium is renewed. After that, their UCVA progressively improves. At some point between 1 week and 1 month postoperatively, their UCVA equals that of LASIK patients, so at 1 month after the surgery the UCVA does not show statistical difference between both groups. During those first postoperative weeks when their UCVA is still improving, all of the LASEK patients could do their normal activities and were not restricted by their UCVA level. Snellen visual acuity is just one of several indicators of visual function. Other aspects of the visual function are probably not well represented solely by UCVA. The statistically significant better results obtained in BSCVA after LASEK compared with LASIK in the current study may be not clinically relevant, but may suggest that other more sensitive parameters of visual function could also be better after LASEK for low myopia than after LASIK. Our study did not measure contrast sensitivity or aberrometry, which could have helped validate this hypothesis. 144 More LASIK-treated eyes required retreatment, although the difference between the two procedures did not reach statistical significance. Perhaps our series did not reach a sufficient number of patients to be able to confirm that tendency with statistically significant difference. Studies with more patients may show an increased power. Nevertheless, caution is advised when interpreting the retreatment rate in LASEK, because the level of postoperative discomfort in this procedure might preclude some patients from accepting a retreatment procedure. An added advantage of using LASEK in this patient population is the absence of stromal flap-related complications that can occur in LASIK, which may cause patient dissatisfaction, especially in this highly demanding population. In our series, no stromal flap complications occurred, but even with the most careful technique to minimize intraoperative complications, other postoperative complications such as diffuse lamellar keratitis or flap avulsion due to trauma may appear, which are avoided with LASEK. Nevertheless, the complication that most ophthalmologists fear is postoperative LASIK ectasia, even in patients with low refractive defect. Laser epithelial keratomileusis minimizes the risk of having this complication, while obtaining equal (or, as suggested by our study, even better) refractive results. On the other hand, problems related to superficial ablations (haze and regression) are minimal after treating low refractive errors, thus avoiding the need to use mitomycin C. 19 We did not register any postoperative haze higher than grade I in our LASEK patients. journalofrefractivesurgery.com JRS0207LLOPIS.indd 144 1/30/2007 9:59:58 AM

7 Considering the results of the current study, we conclude that the choice between LASIK and LASEK for treating low myopia when patients are candidates for both procedures because of an adequate corneal thickness, normal corneal epithelium, and the absence of a risk of trauma, may be based on the faster visual rehabilitation after LASIK or the lower risk of complications in LASEK. We believe that, as far as treatment of low myopia is concerned, LASEK is safer, as it implies less potential risk of complications, especially in the long-term, and offers excellent visual and refractive outcomes. If we take into account the risk/benefit ratio, the relatively low benefit of these patients due to their low refractive error compels us to choose a safer procedure such as LASEK. Laser epithelial keratomileusis and LASIK have both shown to be effective and safe procedures to correct low myopia. Visual recovery is slower after LASEK, but the BSCVA and safety index are slightly better with this procedure than with LASIK. More studies including other parameters of visual function are needed to further elucidate the possible benefits of LASEK for patients with low myopia. REFERENCES 1. Taneri S, Zieske JD, Azar DT. Evolution, techniques, clinical outcomes and pathophysiology of LASEK: review of the literature. Surv Ophthalmol. 2004;49: Potgieter FJ, Roberts C, Cox IG, Mahmoud AM, Herderick EE, Roetz M, Steenkamp W. Prediction of flap response. J Cataract Refract Surg. 2005;31: Tran DB, Saryba MC, Bor Z, Garfis C, Duh YJ, Soltes CR, Juhasz T, Kurtz RM. Randomized prospective clinical study comparing induced aberrations with IntraLase and Hansatome flap creation in fellow eyes: potential impact on wavefront-guided laser in situ keratomileusis. J Cataract Refract Surg. 2005;31: Vinciguerra P, Camesasca FI, Randazzo A. One-year results of butterfly laser epithelial keratomileusis. J Refract Surg. 2003;19: S223-S Partal AE, Rojas MC, Manche EE. Analysis of the efficacy, predictability and safety of LASEK for myopia and myopic astigmatism using the Technolas 217 excimer laser. J Cataract Refract Surg. 2004;30: Claringbold TV. Laser-assisted subepithelial keratectomy for the correction of myopia. J Cataract Refract Surg. 2002;28: Shahinian L. Laser-assisted subepithelial keratectomy for low to high myopia and astigmatism. J Cataract Refract Surg. 2002;28: Taneri S, Feit R, Azar DT. Safety, efficacy and stability indices of LASEK correction in moderate myopia and astigmatism. J Cataract Refract Surg. 2004;30: Vandorselaer T, Hermiat JJ, Schraepen P, Trau R, Tassignon MJ. LASEK for myopia: first results. Bull Soc Belge Ophthalmol. 2003;290: Lee JB, Seong GJ, Lee JH, Seo KY, Lee YG, Kim EK. Comparison of laser epithelial keratomileusis and photorefractive keratectomy for low to moderate myopia. J Cataract Refract Surg. 2001;27: Autrata R, Rehurek J. Laser-assisted subepithelial keratectomy for myopia: two-year follow-up. J Cataract Refract Surg. 2003;29: Litwak S, Zadok D, García-de Quevedo V, Robledo N, Chayet AS. Laser-assisted subepithelial keratectomy versus photorefractive keratectomy for the correction of myopia: a prospective comparative study. J Cataract Refract Surg. 2002;28: Pirouzian A, Thornton JA, Ngo S. A randomized prospective clinical trial comparing laser subepithelial keratomileusis and photorefractive keratectomy. Arch Ophthalmol. 2004;122: Hashemi H, Fotouhi, A, Foudazi H, Sadeghi N, Payvar S. Prospective, randomized, paired comparison of laser epithelial keratomileusis and photorefractive keratectomy for myopia less than diopters. J Refract Surg. 2004;20: Kim JK, Kim SS, Lee HK, Lee IS, Seong GJ, Kim EK, Han SH. Laser in situ keratomileusis versus laser-assisted subepithelial keratectomy for the correction of high myopia. J Cataract Refract Surg. 2004;30: Scerrati E. Laser in situ keratomileusis vs. laser epithelial keratomileusis (LASIK vs. LASEK). J Refract Surg. 2001;17:S219-S Kaya V, Oncel B, Sivrikaya H, Yilmaz OF. Prospective, paired comparison of laser in situ keratomileusis and laser epithelial keratomileusis for myopia less than diopters. J Refract Surg. 2004;20: Gabler B, Winkler von Mohrenfels C, Herrmann W, Gura F, Lohmann CP. Laser-assisted subepithelial keratectomy enhancement of residual myopia after primary myopic LASEK: six-month results in 10 eyes. J Cataract Refract Surg. 2003;29: Lin N, Yee SB, Mitra S, Chuang AZ, Yee RW. Prediction of corneal haze using an ablation depth/corneal thickness ratio after laser epithelial keratomileusis. J Refract Surg. 2004;20: JRS0207LLOPIS.indd 145 1/30/2007 9:59:58 AM