At the end of the 20th century, femtosecond laser technology entered the field of refractive surgery. Several sophisticated excimer laser systems are available, with laser in situ keratomileusis (LASIK) remaining the most popular procedure.1–3 Due to continuous improvements, the correction of myopia up to −8.00 diopters (D) is considered to be safe and predictable and excimer laser–based LASIK has gained wide acceptance worldwide. The long-term results of photorefractive keratectomy and LASIK have been published with up to 18 years of follow-up.4–6
A new procedure that no longer requires an excimer laser, called femtosecond lenticule extraction (FLEx), was first reported by Sekundo et al.7 in 2008. In FLEx, both the flap and the refractive lenticule are created in a one-step procedure using a femtosecond laser. Results of the first 108 eyes were published8,9 and followed up to 5 years.10 Continuous improvements in the surgical performance, energy settings, and laser technology have reached the point that a lifting of the flap is no longer necessary and the procedure can now be performed via a small incision, the so-called small incision lenticule extraction (SMILE).11,12
Nevertheless, this new procedure has to prove long-term stability in the correction of the refractive error. This follow-up study of the first treated prospective group of patients was designed to investigate the long-term results in the first eyes treated with the FLEx procedure 10 years ago. To the best of our knowledge, these are the first 10-year results on this topic.
Patients and Methods
This study was approved by the Ethics Committee of the Chamber of Physicians of Thuringia, Germany. All patients who had been treated in the initial prospective study in 2006–2007 received a written invitation for a reevaluation after 10 years on a voluntary basis. An informed consent was obtained from each patient. A total of 77 eyes from 40 patients were recruited and reevaluated. The mean age was 46 years (range: 31 to 73 years; the minimum age in the original study was 21 years).
In the original study in 2006–2007, patients' mean age at the time of surgery was 35 years (range: 21 to 62 years; n = 108 eyes). There were 55 (51%) left and 53 (49%) right eyes. The mean preoperative spherical equivalent was −4.59 ± 1.30 diopters (D) (range: −8.50 to −2.50 D) with mean preoperative sphere of −4.26 ± 1.35 D (range: 0.00 to −8.50 D) and mean myopic astigmatism of −0.66 ± 0.85 D cylinder (range: 0.00 to −6.00 D).
The FLEx treatment is described in detail elsewhere in the literature.7,8,10
The following parameters were obtained at the 10-year reevaluation visit: uncorrected (UDVA) and corrected (CDVA) distance visual acuity in logMAR units; objective and manifest refraction; pachymetry (AC Master; Carl Zeiss Meditec, Jena, Germany); Goldmann applanation tonometry; and slit-lamp examination with inspection of the interface and corneal surface to record long-term side effects (eg, corneal scars, corneal ectasia, persistent dry eye symptoms, or cataract formation) were recorded and other unrelated ocular pathology excluded (glaucoma or macular disorders).
All measured data were collected on standardized study spread sheets. Statistical analysis was performed using Excel for MAC 2011 (Microsoft Corporation, Redmond, WA) and SPSS Statistics version 21 (IBM Corporation, Armonk, NY). The Wilcoxon signed-rank test was used to compare mean outcomes.
The 10-year visit was accomplished by 40 patients (77 eyes). The results 10 years after the first FLEx study are shown in the “Nine Standard Graphs for Corneal Refractive Surgery” in Figure 1.
Nine standard graphs for corneal refractive surgery. UDVA = uncorrected distance visual acuity; CDVA = corrected distance visual acuity; SEQ = spherical equivalent; D = diopters; TIA = target induced astigmatism; SIA = surgically induced astigmatism
Because the FLEx procedure was a novel surgical approach 10 years ago, the change in CDVA still represents the most important value. As shown in Figures 1A–1C, none of the patients lost two or more Snellen lines of CDVA and 5 eyes of 5 different patients had a loss of one Snellen line after 10 years. Figure 2 presents the CDVA over 10 years in logMAR units, giving the number of eyes at the examinations at 1 and 6 months and 1, 5, and 10 years after surgery. Figure 3 presents the same for UDVA over 10 years in logMAR units.
Corrected distance visual acuity (CDVA) 10 years after femtosecond lenticule extraction shown in logMAR units.
Uncorrected distance visual acuity (UDVA) 10 years after femtosecond lenticule extraction shown in logMAR units.
In the first eyes treated with this new refractive procedure, the target was not set at plano but at −0.75 D (−0.52 ± 0.23 D) to avoid a shift to hyperopia. This target is in line with the presented data after 10 years. The data of the attempted versus achieved correction of 77 eyes after 10 years is given in Figures 1D–1E.
The refraction in the group was stable from the start of the study to the 10-year results (Figure 1F).
All patients were treated for dry eye symptoms within the first 3 months after FLEx. At the 10-year follow-up, no signs of keratectasia or other late complications were found. The pachymetry showed an increase of 30 µm over the 10-year period (Figure 4).
Pachymetry of the eyes treated in 2006–2007 at the 10-year follow-up.
Femtosecond laser systems have an outstanding importance in the refractive market.13,14 With regard to the quality of the surgical outcome and safety, femtosecond lasers have clearly proven advantages over mechanical devices.15–17 Ideally, an advanced femtosecond laser system should be able to perform a one-step, rapid refractive procedure accompanied by further reduction of possible complications.18
FLEx is still a relatively new surgical procedure. This first study ever done used the “old” 200-kHz VisuMax laser (Carl Zeiss Meditec) and started without a nomogram. As a matter of fact, in the first eyes treated by FLEx in 2006, predictability was not as good as with the LASIK procedure at the same time. The results for astigmatic correction clearly demonstrated the need for new nomograms (Figures 1G–1I). The results have been published in the literature and advances in laser technology, energy settings, and laser scan patterns translated into much superior outcomes.11,19 A 500-kHz VisuMax femtosecond laser is currently in use and less tissue damage and inflammation were reported in the animal studies supporting clinical impressions.20 In the last generation of studies, SMILE delivered refractive outcomes superior to the first results with the 2006 technology presented here and comparable to LASIK outcomes. Therefore, predictability is no longer a major concern.
Besides the safety of the surgery itself, the predictability of long-term stability is of prime importance. Approximately 50% of eyes remain within ±1.00 D of the intended correction 6 to 10 years after LASIK, which is largely dependent on the degree of correction.4,6 High myopia is known to be a risk factor for long-term regression after laser refractive surgery.21 Although long-term photorefractive keratectomy and LASIK results have been published with up to 18 years of follow-up, the longest follow-up for FLEx and SMILE has only been 5 years.
To establish the regression rate after FLEx and SMILE, a long-term follow-up period is needed. Our results show that the stability of the achieved correction seems to be one of the major advantages of the FLEx procedure. In LASIK for myopia, a mean regression of up to 0.97 D has been reported after long-term follow-up.4,6 The data presented in this study 10 years after FLEx are better, with a mean regression of 0.18 D.
Similar to patients treated with LASIK, all patients who had FLEx were treated for dry eye symptoms within the first 3 months after the procedure.9 No further treatment was required thereafter. This is in line with published data on corneal sensitivity: postoperative alteration of corneal sensitivity was similar after FLEx surgery compared to femtosecond laser–assisted LASIK vision correction.22 No late side effects were detected in our long-term investigation.
Visual outcomes in the current study also echo the previous literature. No patients lost two or more lines of CDVA. Some of the patients have now reached the age where cataract formation is responsible for some reduction in visual acuity. Therefore, the problem of intraocular lens calculation after refractive surgery is being addressed by our research group.
Limitations of the current study include the limited number of eyes. Some of the original 108 eyes were lost to follow-up. Furthermore, due to the design of the initial “proof of principle” study in 2006–2007, we can only compare data that were collected in the first study 10 years ago; we therefore cannot give data on some interesting questions. In a study by Wu and Wang,23 FLEx refractive surgery induced significantly higher coma than LASIK. In another study, FLEx showed significantly less induction of higher order aberrations after 1 year.24 A relatively small optical zone might be the reason because it was reported that a smaller optical zone could result in complaints about optical quality.25 Previous studies on photorefractive keratectomy and LASIK indicated that the optical zone had a significant impact on higher order aberrations.26,27 Furthermore, decentration might play an important role and there is a need for further research.28
These first 10-year outcomes of FLEx refractive surgery produced results that were remarkably stable and without any late complications. Because FLEx has gained worldwide popularity since the introduction of the flap-free SMILE technique, the current investigation might alleviate remaining concerns among surgeons in terms of stability and late complications of this new treatment modality.
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- Alió JL, Muftuoglu O, Ortiz D, et al. Ten-year follow-up of laser in situ keratomileusis for myopia of up to -10 diopters. Am J Ophthalmol. 2008;145(1):46–54. doi:10.1016/j.ajo.2007.09.010 [CrossRef]
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- Sekundo W, Kunert K, Russmann C, et al. First efficacy and safety study of femtosecond lenticule extraction for the correction of myopia: six-month results. J Cataract Refract Surg. 2008;34(9):1513–1520. doi:10.1016/j.jcrs.2008.05.033 [CrossRef]18721712
- Blum M, Kunert KS, Schröder M, Sekundo W. Femtosecond lenticule extraction (FLEx) for the correction of myopia: 6 months results. Graefes Arch Clin Exp Ophthalmol. 2010;248:1019–1027. doi:10.1007/s00417-009-1293-1 [CrossRef]20130899
- Blum M, Kunert KS, Engelbrecht C, Dawczynski J, Sekundo W. Femtosecond lenticule extraction (FLEx): results after 12 months in myopic astigmatism [article in German]. Klin Monatsbl Augenheilkd. 2010;227(12):961–965. doi:10.1055/s-0029-1245894 [CrossRef]21157666
- Blum M, Flach A, Kunert KS, Sekundo W. Five-year results of refractive lenticule extraction. J Cataract Refract Surg. 2014;40(9):1425–1429. doi:10.1016/j.jcrs.2014.01.034 [CrossRef]25135533
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- Sekundo W, Kunert K, Blum M. Small incision femtosecond lenticule extraction (SMILE) for the correction of myopia and myopic astigmatism: results of a 6 months prospective study. Br J Ophthalmol. 2011;95:335–339. doi:10.1136/bjo.2009.174284 [CrossRef]
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