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A retrospective comparison of efficacy and safety of 680 consecutive lasik treatments for high myopia performed with two generations of flying-spot excimer lasers

2010; Wiley; Volume: 89; Issue: 8 Linguagem: Inglês

10.1111/j.1755-3768.2009.01830.x

1755-3768

Lola Gazieva, Mette Hjuler Beer, Kim Nielsen, Jesper Hjortdal,

Ocular Surface and Contact Lens

Purpose: To compare the visual refractive outcome and complication of laser in situ keratomileusis (LASIK) carried out with a Carl Zeiss-Meditec MEL-70 Excimer laser and a MEL-80 laser for treatment of high myopia. Methods: Journal records of 680 consecutive eyes that underwent LASIK with a Schwind Supratome microkeratome and a MEL-70 Excimer laser (Group A), or a Moria M2 microkeratome and a MEL-80 Excimer laser (Group B) were reviewed. Manifest refraction, uncorrected and best spectacle-corrected visual acuity (BSCVA), corneal topography and central corneal thickness (CCT) were recorded before and 3 months after treatment. Pre- and postoperative complications, visual and refractive outcome and frequency of retreatments were registered. Results: Mean preoperative spherical equivalent refraction was −8.52 dioptres (−5.50–−18 dioptres), and the mean attempted laser correction was −8.02 dioptres (−5.50–−11 dioptres). Three months after LASIK, the average treatment error (difference between achieved and attempted correction) was 1.20 (SD = 1.19) dioptres of under correction in Group A and 0.52 (SD = 1.00) dioptres in Group B. Four eyes lost more than two lines of BSCVA (0.6%). In 110 eyes (16%), a re-LASIK procedure was performed to reduce remaining myopia after the primary procedure. Conclusions: Laser in situ keratomileusis treatment for high myopia can effectively reduce high degrees of myopia. Under correction was observed in both treatment groups but Group B has a slightly better predictability. Significant loss of BSCVA occurs infrequently after LASIK for even considerable grades of myopia (0.6% in each group). Laser-assisted in situ keratomileusis (LASIK) has become the most widely used form of refractive surgery (Condon et al. 1997; Bokobza & Burtin 2000; Lin & Tsai 2005). The objective of this surgical technique is to modify the anterior corneal shape by ablating tissue from the stroma by means of the Excimer laser after creating a hinged corneal flap. Continuous improvements in the original technique have made the surgical procedure safer, more accurate and repeatable. These progressions are because of the development of new surgical instrumentation aimed for improving visual outcome and safety of the surgical procedure (Goes 2008). The results of LASIK are affected by various factors such as age, type of laser, type of microkeratome, preoperative sphere and cylinder and preoperative best spectacle-corrected visual acuity (BSCVA) (Sakimoto et al. 2006; Ghanem et al. 2007; Kojima et al. 2008). Despite the very large number of yearly procedures, a review of current literature revealed only few reports of studies including many consecutive eyes treated for high myopia. The range of preoperative myopia often varies from study to study and often no distinction is made between primary treated and retreated eyes when efficacy and complications are quoted. Since 1999, LASIK operations have been performed at Department of Ophthalmology, Aarhus University Hospital (Beer et al. 2005). The objective of this study was to evaluate all bilateral LASIK operation for high myopia at Department of Ophthalmology, Aarhus University Hospital during two consecutive periods, each of approximately 2 years. The aim of this study was to compare the visual refractive outcomes and complications of LASIK carried out with a Schwind Supratome microkeratome and Carl Zeiss-Meditec MEL-70 Excimer laser or a Moria M2 microkeratome and Carl Zeiss-Meditec MEL-80 Excimer laser for treatment of high myopia (more than 5.50 dioptres of myopia). Two retrospective reviews of consecutive patients treated for bilateral myopia higher than 5.50 dioptres (spherical equivalent) were carried out. The inclusion criteria were LASIK treatment of both eyes for myopia of more than −5.5 D, 21 years of age or older. Exclusion criteria were preoperative astigmatism of 2.50 dioptres or more, ocular disease, previous refractive surgery or systemic disease likely to affect epithelial healing. The first review (Group A) included patients who were operated in the period from 1 April 2001 to 1 April 2003 with LASIK using a MEL-70 Excimer laser (Carl Zeiss Meditec, Jena, Germany) and a Schwind Supratome microkeratome with a 130 μm head (Schwind, Kleinostheim, Germany). The second review (Group B) consisted of patients who were operated in the period from 1 May 2005 to 1 August 2006 with LASIK using a MEL-80 Excimer laser (Carl Zeiss-Meditec) and a Moria M2 microkeratome with a 130 μm head (Moria, Antony, France) (Group B). All examinations and operations were performed at Department of Ophthalmology, Aarhus University Hospital. All eyes were operated by the same surgeon. A total of 680 eyes were included, 326 eyes in Group A and 354 eyes in Group B. The preoperative evaluation included uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), cycloplegic refraction, slit-lamp examination, keratometry, pneumotonometry, corneal pachymetry, mesopic pupil size measurement using a Procyon pupilometer, corneal topography TMS-3 (Tomey, Nagoya, Japan) or ATLAS (Carl Zeiss Meditec) and dilated fundus examination. Surgery was performed under topical anaesthesia after instillation of two drops of 0.8% oxybuprocaine. Microkeratome suction rings were chosen according to the manufacturers instructions. Flaps were superiorly hinged. Patients were asked to look on the fixation light of the laser, and eye-tracking was started. The laser was in most cases centred at the pupil centre. If the distance between the pupil centre and the corneal vertex, defined as the specular reflex of the fixation light, was more than 0.5 mm, the centre for the laser treatment was moved one-third of the distance towards the corneal vertex (Mandell 1995). In most cases, a laser ablation zone of 6.00 was used, and standard sphero-cylindrical ablations were used in all cases. A residual stromal bed of at least 250 μm was always aimed for. In some patients, the attempted correction change was therefore less than the manifest refraction. After replacement of the flap, the eye was allowed to dry for 2 min, and one drop of chloramfenicol, 5 mg/ml (Nycomed, Roskilde, Denmark) and one drop of non-preserved diclofenac, 1 mg/ml (Voltaren; Novartis, Copenhagen, Denmark) were instilled. The patients were asked to rest with their eyes closed for 2–3 hr after surgery. The postoperative regime after LASIK in Group A included chloramfenicol eye drops four times per day for 1 week. In Group B, standard postoperative treatment was chloramfenicol drops and prednisolone eye drops, 5 mg/ml (Ultracortenol; Novartis) four times per day for 1 week and two times daily for another week. In addition, patients were asked to use additional viscous eye drops if they felt drying of their eyes. All patients were offered examination the first day postoperatively. UCVA was measured and examination with slit-lamp focused on postoperative complications in terms of interface debris, flap folds and inflammatory reaction. At 3 months UCVA, BSCVA, subjective spherical and cylindrical refraction, pachymetry, tonometry, topography and complications in terms of interface debris, epithelial ingrowth and flap folds were registered. The safety of the procedures was evaluated by recording intraoperative complications (frequency of incomplete or free-flap, epithelial defect), and postoperative complications (epithelial ingrowths, interface inflammation, infection), by calculation of the safety index (ratio between BSCVA 3 months after surgery and BSCVA before surgery), and by calculating the number of eyes that lost more than two Snellen lines in BSCVA. The efficacy of the procedures was evaluated by computation of the difference between attempted and achieved refractive change at 3 months after surgery, the efficacy index (ratio between UCVA 3 months after surgery and BSCVA before surgery) and frequency of eyes with UCVA above 0.5. UCVA was only used for evaluation of efficacy for eyes in which the attempted correction was within 0.50 dioptre of attempted emmetropia. Dissatisfied patients with unexpected ametropia were offered retreatment if this was possible within the respect of a residual stromal bed of 250 μm. Retreatments were performed within 3–6 months after primary LASIK. The flap was manually relifted with a Sinskey hook, laser treated and after replacement of the flap the retreated eyes received the same postoperative treatment, and the follow-up time was the same as for the primary treated eyes. Student’s t-tests were used for statistical analysis of differences in efficacy and safety between the two treatment groups. As the two eyes of the same subject are not independent, the number of subjects rather than the number of eyes was used in the statistical comparisons. The preoperative data are summarized in Table 1. The spherical equivalent refractive error was slightly larger in Group A, and patient age was slightly higher in Group B. Emmetropia within 0.5 dioptre could be aimed for in 217 eyes in Group A (67%) and in 251 eyes in Group B (71%). Three months follow-up data were available in 314 eyes in Group A (96%) and in 280 eyes in Group B (79%). After primary surgery, there was higher residual myopia in Group A compared to Group B (Table 2). At day 1, an UCVA ≥ 0.5 was obtained in 72% (156 eyes) in Group A and in 79% (198 eyes) in Group B. Three months after surgery, the percentage of patients with UCVA ≥ 0.5 was reduced to 50% (108 eyes) in Group A and to 73% (123 eyes) in Group B. The efficacy index which is the ratio of mean postoperative UCVA to mean preoperative BSCVA was 0.54 ± 0.36 (SD) for Group A and 0.67 ± 0.33 (SD) for Group B. The difference is statistically significant with Group B being superior to Group A (p < 0.01). Figure 1A for Group A; 1B for Group B, show the relation between attempted and achieved change in refraction after LASIK treatment. The mean standard deviation of the remaining refractive error defined as the difference between attempted and achieved correction was −1.20 ± 1.19 D in Group A and −0.52 ± 1.00 D in Group B. This difference was statistically significant (p < 0.01). A and B show the remaining refractive error after laser in situ keratomileusis (LASIK) treatment in Group A and Group B, respectively. Results of primary LASIK are shown by (•) and results of re-LASIK by (^). The percentage of eyes within ± 0.5 D; ± 1.0 D and ± 2.0 D 3 months after primary treatment is presented in Table 3. In Group A 17% (54 eyes) of patients and in Group B 15% (54 eyes) of patients were retreated to reduce ametropia further. After retreatment, the mean remaining refractive error in these retreated eyes was −0.47 ± 0.66 D in Group A and −0.43 ± 0.43 D in Group B. There was no significant difference between the residual refractive errors in the two groups. Table 4 presents percentage of retreated eyes that were within ± 0.5 D; ± 1.0 D and ± 2.0 D. Intraoperative complications were few in both groups. After primary treatment, interface debris occurred in 57 eyes, (17%) in Group A and four eyes (1%) in Group B. Peripheral epithelial ingrowths was seen in 11 eyes, (3%) in Group A but in none in Group B. After retreatment, interface debris occurred in 16 eyes (29.6%) in Group A and one eye (2%) in Group B. Epithelial ingrowths were observed in 15 eyes (28%) in Group A and in one eye (2%) in Group B. Even discrete interface debris and epithelial ingrowths were registered. All cases of epithelial ingrowths were clinically insignificant and were left untreated. Complications were more common after retreatments than after primary treatment. Two eyes lost two or more lines of BSCVA after primary LASIK in each of the two groups (0.6%). The mean safety index, which is the ratio of mean postoperative BSCVA to mean preoperative BSCVA, was 1.07 ± 0.21 for Group A and 1.00 ± 0.18 in Group B. There was no significant difference between the safety index in the two groups, and the indices were not significantly different from one. After retreatment, one eye in each group lost two or more lines (2%). The safety index was 1.00 ± 0.20 in Group A and 0.91 ± 0.14 in Group B. There was no significant difference between the safety index in the two groups, and the indices were not significantly different from one. This study represents an assessment of the quality of two LASIK treatment protocols as it can take place in hospital clinical practice. In Denmark, which operates with a fully socialized medical system, patients with more than 6 dioptres of myopia in both eyes can be offered refractive surgery free of charge, if they have difficulties wearing contact or spectacle correction. Patients treated were referred from the whole country of Denmark. All patients who were treated and retreated in periods from 1 April 2001 to 1 April 2003 and from 1 May 2005 to 1 August 2006 with a Schwind Supratome microkeratome + a Carl-Zeiss Meditec MEL-70 Excimer laser or a Moria M2 microkeratome + a Carl-Zeiss Meditec MEL-80 Excimer laser, respectively, were included. The review included a large number of consecutive patients (342 individuals) who were treated bilaterally (680 eyes) for high myopia. In our study, we compared the two lasers in terms of visual outcomes, predictability and safety. In both groups, LASIK treatment for high myopia resulted in a significant reduction in the degree of myopia. However, there was some degree of unreliability on the accuracy of the treatment with a tendency to an under correction. Serious complications and significant loss of visual acuity occurred infrequently. All of the 680 treated eyes in our study were high myopic (range −5.50–−18 D). Reviewing literature for the past few years reveals few reports including large numbers of eyes treated with LASIK for high myopia. Making comparisons between studies can be difficult because of e.g. variation in the range of preoperative myopia, length of follow-up periods, laser nomograms, microkeratomes and techniques. Because of the continuous evolution of LASIK technology and techniques, it is also difficult to extrapolate results in literature that are comparable to current practices that use the most recent generations lasers (Goes 2008). Intraoperative complications were few for both laser types. Postoperative complications as interface debris and peripheral epithelial ingrowth were more often seen with the Schwind Supratome microkeratome and Carl-Zeiss Meditec MEL-70 laser (A), especially after retreatment (interface debris in 29.6%, peripheral epithelial ingrowth in 28% versus 2% and 2% with the Moria M2 microkeratome and Carl-Zeiss Meditec MEL-80 laser (B)). None of the complications influenced significantly on visual outcome after 3 months. The difference in percentage of eyes with postoperative complications might be explained by change in postoperative medication (steroid drops were introduced for Group B). It also seems that a better edge configuration of the flap may be obtained with the Moria M2 microkeratome than with the Schwind Supratome microkeratome, which may explain why epithelial ingrowth occurred less frequently in Group B. The percentage of complications in our study (Group B) is similar to or lower than reported from other studies (Lyle & Jin 2000, 2001; Bragheeth et al. 2008). The number of eyes that lost two or more lines of BSCVA was the same for both laser types (two eyes (0.6%) from each group after primary treatment and one eye (2%) from each group after retreatment). The loss of BSCVA was not statistically significant when safety index was calculated and is low or similar to that reported from other studies. Lyle & Jin (2000) reported of 1.3% of eyes that lost two or more lines of pre-LASIK BSCVA after retreatment. Lyle & Jin (2001) reported of 1.8% of eyes (−10–−18 D, mean SE −11.69 ± 1.46 D) that lost two or more lines of BSCVA after primary treatment. Lin & Tsai (2005) reported of 1.82% of primary treated eyes that lost two or more lines of BSCVA (mean SE −7.13 ± 2.87 D, range −3.00–−16.00 D). It has been observed that the predictability and efficacy after LASIK for myopia vary with the degree of attempted correction with lower efficacy and predictability and a tendency towards under correction in patients with high myopia (Lyle & Jin 2001; Lin & Tsai 2005; Kojima et al. 2008). In our study, an UCVA ≥ 0.5 at 3 months was obtained by 50% and 73%, respectively, in the two groups after primary treatment. The residual refractive error after primary LASIK treatment was significantly lower in the group of eyes treated with the latest generation of lasers (−1.20 ± 1.19 D versus −0.52 ± 1.00 D). The initial refractive error was larger in Group A compared with Group B, but this difference cannot explain the difference in efficacy, as there was only a modest effect of attempted correction on residual refractive error (0.05 dioptre higher residual error per attempted dioptric change in refraction, as calculated by linear regression analysis). The efficacy index (mean postoperative UCVA to mean preoperative BSCVA) was significantly different between the two groups, with the group of patients treated with the latest generation of laser being superior to the other group, whereas there was no significant difference in the refractive error after retreatment. Kojima et al. (2008) reported of a high myopia cohort (−6–−10 D) where 56.9% achieved an SE within ± 0.50 D and 93.1% achieved UCVA ≥ 0.5, which are better results than ours, but in a group with slightly lower degree of myopia than in our study. Lyle & Jin (2001) report of 89.5% with UCVA ≥ 0.5 and a residual refractive error of −0.37 ± 0.80 D for a high myopia group (−10–−18 D). Thirty-seven percent of these eyes did however include retreatment. The percentage of retreated eyes in our study was fairly low (16%), considering the degree of preoperative myopia compared to other studies (Kojima et al. 2008; Lyle & Jin 2000; Alió et al. 2008). Not all studies make distinction between primary (single LASIK) treated and retreated eyes when efficacy is quoted, which also may explain why efficacy seems lower in our study (Lin & Tsai 2005; Kojima et al. 2008). This study was limited by only 3 months of follow-up time, although it seems that postoperative refraction is fairly stable at this time following LASIK (Rashad 2000; Bragheeth et al. 2008). The most serious long-time side-effect of LASIK is progressive ectasia (Seiler & Quurke 1998). We are not aware that any of the 342 patients have developed ectasia over the years since treatment. The Department of Ophthalmology, Aarhus University Hospital is a national centre for complicated corneal and refractive surgery, and we assume that any case of corneal ectasia would have been referred to us. Follow-up rates were high (99% at day 1 and 96% and 79% in Groups A and B, respectively, at 3 months) but it is tempting to assume that patients who were not interested to spend time on the 3 months follow-up possibly had fairly good uncorrected visual acuity. Efficacy, predictability and stability results may have been better if all patients were examined at the offered 3 months follow-up visit. In conclusion, both lasers are effective, fairly predictable and safe for correcting myopia up to −10 dioptres. Better predictability and fewer postoperative complications were observed in the group of patients treated with the Moria M2 microkeratome and MEL-80 Excimer laser compared to patients who underwent treatment with a Schwind Supratome and MEL-70 Excimer laser. It can be the result of several factors such as refinement of laser apparatus and microkeratomes, more experience in this kind of surgery or change in postoperative medication. It is important to inform patients seeking corneal refractive surgery for high myopia, that emmetropia cannot always be expected, but that a safe and significant reduction in myopia is possible in almost all cases.