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 Table of Contents  
ORIGINAL ARTICLE
Year : 2014  |  Volume : 4  |  Issue : 4  |  Page : 156-162

Outcome of a 10-year follow-up of laser in situ laser keratomileusis for myopia and myopic astigmatism


1 Minamiaoyama Eye Clinic; Department of Ophthalmology, School of Medicine, Keio University, Tokyo, Japan
2 Minamiaoyama Eye Clinic; Department of Ophthalmology, National Defense Medical College, Saitama, Japan
3 Minamiaoyama Eye Clinic, Tokyo, Japan
4 Department of Ophthalmology, School of Medicine, Keio University, Tokyo, Japan

Date of Web Publication1-Oct-2014

Correspondence Address:
Takeshi Ide
Minamiaoyama Eye Clinic, Renai Aoyama Building 4F, 3-3-11, Kitaaoyama, Minato-ku, Tokyo 107-0061
Japan
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Source of Support: None, Conflict of Interest: None


DOI: 10.1016/j.tjo.2014.06.002

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  Abstract 


Purpose: To evaluate the results of laser in situ laser keratomileusis (LASIK) for myopia/myopic astigmatism over a 10-year period.
Methods: We examined LASIK patients who received regular postoperative assessments over 10 years. We evaluated uncorrected visual acuity (UCVA), manifest refraction, best-corrected visual acuity, intraocular pressure, retreatment rate, safety, efficacy, and complications.
Results: We studied 5423 eyes between December 1997 and February 2002. The study criteria were met by 346 eyes. A UCVA of 20/40 was achieved in 86.1% of the patients, with 52.0% achieving 20/20 at 10 years. Refraction within 1.00 σ of target was achieved in 76.3% of the patients, and 95.7% were within 2.00 σ at 10 years. Retreatment was required in 124 eyes (35.8%). The preoperative logMAR UCVA of 1.24 improved to −0.08 at 1 month, and slightly decreased to 0.06 at 10 years. The safety and efficacy indices were 1.0 and 0.89 at 1 month, and 0.99 and 0.71 at 10 years.
Conclusion: We analyzed 6.3% of patients who regularly returned for postoperative examinations. Despite the relatively low 10-year-visit rate and the inclusion of single- and multiple-treatment cases, our results may represent the real-world picture of LASIK; furthermore, our study shows that LASIK is an effective and safe procedure.

Keywords: astigmatism, follow-up studies, laser in situ laser keratomileusis, myopia


How to cite this article:
Ide T, Toda I, Fukumoto T, Watanabe J, Tsubota K. Outcome of a 10-year follow-up of laser in situ laser keratomileusis for myopia and myopic astigmatism. Taiwan J Ophthalmol 2014;4:156-62

How to cite this URL:
Ide T, Toda I, Fukumoto T, Watanabe J, Tsubota K. Outcome of a 10-year follow-up of laser in situ laser keratomileusis for myopia and myopic astigmatism. Taiwan J Ophthalmol [serial online] 2014 [cited 2019 Nov 20];4:156-62. Available from: http://www.e-tjo.org/text.asp?2014/4/4/156/204132




  1. Introduction Top


Laser in situ laser keratomileusis (LASIK) was introduced in the early 1990s and became the most-performed refractive surgery in the 2000s.[1]

Since refractive surgery is performed mostly in young and healthy eyes of patients with high expectations, its long-term safety and efficacy are of great concern.[2] The efficacy and safety of LASIK have been reported by several investigators; however, most of these reports have summarized postoperative outcomes over a relatively short period.[3],[4],[5],[6],[7],[8]

We have performed LASIK at our institute since 1997 and have attempted to follow-up and record the postoperative course.

We previously reported the efficacy and safety of LASIK over a 5-year postoperative period.[9] There are only a few reports of longer-term outcomes.[10],[11],[12],[13] The aim of this study was to evaluate the 10-year safety, efficacy, and stability of myopia/myopic astigmatism LASIK performed in our clinic.


  2. Materials and methods Top


2.1. Patient population

At our clinic, we performed LASIK on 26,604 eyes in 13,595 patients from 1997 until the end of 2009, and 5423 eyes with myopia/myopic astigmatism between December 1997 and February 2002. Of the 5423 eyes, 182 patients (346 eyes) regularly returned for follow up and were enrolled in this study. Our exclusion criteria for the study were previous ocular surgery, corneal diseases, glaucoma, history of ocular trauma, and insufficient corneal thickness for laser ablation, or preoperative detection of forme fruste keratoconus (FFKC). Eyes with endothelial cell counts below 1500 cells/mm2 were also excluded. Patient demographics are summarized in [Table 1]. The study was conducted in accordance with the tenets of the Declaration of Helsinki. Written informed consent was obtained from all the patients.
Table 1: Demographics of patients included in this study.

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2.2. Surgical technique

LASIK was performed by our surgeons, using the same technique with minor variations. A corneal flap was created using LSK-One (Moria, Antony, France; 229 eyes), Flapmaker (Solan OphthalmicProducts, Jacksonville, FL, USA; 3 eyes), or MK-2000 (Nidek,Aichi,Japan; 114 eyes) microkeratome. The residual bed thickness (RBT) was measured using the AL-2000 pachymeter (Tomey, Aichi, Japan), although this intraoperative measurement was not performed in the earlier cases.

As a custom treatment was unavailable during this period, conventional ablation was performed using the APEX PLUS

(Summit, Waltham, MA, USA; 81 eyes) or EC-5000 (Nidek; 265 eyes) excimer laser system. In some cases, undercorrection was employed as requested by the patient, but these cases were excluded from this study. After surgery, a low-dose steroid (0.1% fluorometholone; Santen, Osaka, Japan) and a quinolone antibiotic (Tarivid or Cravit; Santen) were prescribed five times/day for the 1st postoperative week. For dry eye care, we prescribed 0.3% preservative-free hyaluronic acid (Hyalein mini; Santen) eye drops five times/day for the 1st postoperative week. Subsequently, we continued the same regimen, switching to less 0.1% hyaluronic acid and/or saline eye drops, or stopping anti–dry-eye medication, depending on the patients’ ocular conditions.

2.3. Retreatments

Retreatments after LASIK were performed by relifting the flap. Disposable contact lens were placed and then removed on postoperative Day 1. The postoperative eye drop regimen was the same as that for the primary surgery.

2.4. Postoperative evaluation

Postoperative examinations were performed at 1 day, 1 week, 1 month, 3 months, and 6 months, and 1 year, 2 years, 3 years, 4 years, 5 years, and 10 years after surgery. In this study, we analyzed the postoperative data at 1 month, 3 month, and 6 months and 1 year, 5 years, and 10 years. Patient visits were not usually at precise time points; therefore, 1–3 years, 4–7 years, and 8–10 years postoperatively were regarded as 1 year, 5 years, and 10 years, respectively. Uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), manifest refraction, intraocular pressure (IOP), and complications were investigated.

Data were obtained at the end of 10 years and evaluated retrospectively, including the following safety and efficacy indices: safety = BCVApost/BCVApre; efficacy = UCVApost/BCVApre.

2.5. Statistical analysis

Data analysis was performed using SPSS 18 (SPSS Inc., Chicago, IL, USA). A p-value <0.05 was considered statistically significant.


  3. Results Top


3.1. Overall result

In this study, 222 eyes of 125 patients underwent single treatment (64.2%), and 124 eyes of 75 patients had two or more treatments (35.8%).

3.2. Refractive change, predictability, and stability

The manifest spherical equivalent (SE) of −6.42 ± 2.70 σ pre-operatively improved to 0.06 ± 0.53 σ at 1 week, −0.05 ± 0.51 σ at 1 month, −0.18 ± 0.62 σ at 3 months, −0.16 ± 0.55 σ at 6 months, −0.15 ± 0.53 σ at 1 year, −0.38 ± 0.69 σ at 5 years, and −0.67 ± 0.92 σ at 10 years. Postoperatively, the mean SE was stable and showed slight regression over 10 years [Figure 1] and [Figure 2]. The percentage of eyes for which a UCVA of 20/40 was achieved was 86.1%, with 52.0% achieving 20/20. At 10 years, 76.3% of eyes achieved refraction within ±1.00 σ of target and 95.7% were within ±2.00 σ of target.
Figure 1: Scattergram of attempted and achieved correction at each time point: (A) 1 month and (B) 10 years after laser in situ laser keratomileusis surgery for the 346 eyes.

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Figure 2: Mean value of the spherical equivalent (SE): manifest refraction decreased gradually after surgery. Small but statistically significant regression up to 10 years.

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The scattergrams of attempted versus achieved correction at 1 month and 10 years postoperatively are illustrated. These graphs show that the higher refractive error cases tend to be under-corrected and that the R2 number is smaller at 10 years than at 1 month, which indicates refractive regression. The timing for enhancement was 5.8 ± 3.5 years after the primary surgery.

The safety (BCVApost/BCVApre) and efficacy (UCVApost/BCVApre)indexes were 1.0 ± 0.17 and 0.89 ± 0.23, 1.0 ± 0.16 and 0.86 ± 0.24, 1.02 ± 0.17 and 0.89 ± 0.24,1.04 ± 0.15 and 0.89 ± 0.22,1.01 ± 0.16 and0.8 ± 0.27, and 0.99 ± 0.18 and 0.71 ± 0.31 at 1 month, 3 months, 6 months, 1 year, 5 years, and 10 years, respectively [Figure 3].
Figure 3: Safety and efficacy index of laser in situ laser keratomileusis surgery up to 10 years. (A) Safety. (B) Efficacy.

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In addition to this trend graph, the scattergrams of attempted correction vs. safety or efficacy at 1 month and 10 years post-operatively are illustrated [Figure 4] and [Figure 5]. The safety approximation lines are located at almost 1 at 1 month and 10 years [Figure 4]. The efficacy lines, however, tended to be lower with higher correction cases both at 1 month and 10 years, and lower at 10 years than at 1 month [Figure 5].
Figure 4: Scattergram of attempted correction and safety index at each time point: (A) 1 month and (B) 10 years after laser in situ laser keratomileusis surgery for 346 eyes.

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Figure 5: Scattergram of attempted correction and efficacy index at each time point: (A) 1 month and (B) 10 years after laser in situ laser keratomileusis surgery for 346 eyes.

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In [Figure 1]B, two cases showed considerable regression of refraction. The first case was of a 17-year-old man who requested for LASIK surgery. We usually perform LASIK surgery in patients above 18 years; however, in July 2011, we performed surgery for both his eyes because he needed a good UCVA score to become a policeman. The preoperative refraction data were OD S–10.0 σ = C–1.0 DA × 170 and OS S–9.5 σ = C–3.0 DA × 180, and the pachymetry was OD 558 υm and OS 562 υm, respectively. He underwent regular checkups. In November 2001, the vision and topography were within normal limits. At the examination in March 2008, his right eye logarithm of the minimum angle of resolution (logMAR) BCVA was 1, the refraction was S–6.0 σ = C–5.5 DA × 160, and the topography showed ectatic change.

The second case involved cataract formation 10 years after LASIK surgery. The patient had bilateral LASIK surgery at the age of 45 in November 1999, and was stable with plano SE manifest until April 2005 without any cataract sign. At the examination in September 2009, slit-lamp examination showed nuclear cataract formation. The refraction was OD S–mination showed nuclear cataract formation. The refraction was 5.5 σ = C–0.75 DA × 40 and OSS–0.5 σ and logMAR BCVA was OD (0.2) and OS (-0.1) respectively. We performed multifocal intraocular lens surgery in her right eye, with visual result of logMAR UCVA −0.1.

3.3. Visual acuity

The UCVA logMAR of the patients was 1.24 ± 0.29 preoperatively and improved to −0.03 ± 0.18 on Day 1 and −0.07 ± 0.16 at 1 week, and reached 0.08 ± 0.16 at 1 month, −0.06 ± 0.2 at 3 months, −0.08 ± 0.17 at 6 months, −0.09 ± 0.15 at 1 year, −0.02 ± 0.2 at 5 years, and 0.06 ± 0.26 at 10 years. [Figure 6] shows very small but continuous and statistically significant decreases in UCVA, reaching 0.06 ± 0.26 at 10 years after surgery.
Figure 6: Changes in uncorrected visual acuity (UCVA). The UCVA (logMAR) improved at 1 day and was stable until 5 years after surgery. Thereafter, UCVA showed a minimal but statistically significant decrease.

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The final BCVA at the 10-year examination improved by two lines in five eyes (1.4%) and was unchanged in 325 eyes (93.9%). However, 15 eyes lost two lines (4.6%) of BCVA [Figure 7] and [Figure 8].
Figure 7: Changes in best-corrected visual acuity (BCVA). The BCVA (logMAR) improved at 1 day and was stable until 10 years after surgery.

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Figure 8: Changes in best-corrected visual acuity (BCVA). The frequency of eyes with refractive BCVA that lost two lines was 4.6% at 10 years after laser in situ laser keratomileusis surgery.

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3.4. IOP

The IOP was 13.4 ± 2.5 mmHg preoperatively. It decreased to 9.6 ± 1.9 mmHg at 1 week and 9.6 ± 2.5 mmHg 1 month after surgery and did not change thereafter [Figure 9]. The scattergram of SE versus IOP reduction showed a trend toward higher treatments causing greater reductions in IOP, although this correlation was not statistically significant [Figure 10].
Figure 9: Changes in intraocular pressure (IOP), which decreased by about 4 mmHg at 1 week after surgery and remained stable thereafter

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Figure 10: Scattergram of corrected power and the IOP reduction at postoperative 3 months.

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3.5. Complications

Diffuse lamellar keratitis (DLK) was observed in six eyes (2.0%), but all were managed with intensive steroid eye drop treatment without surgical intervention. Microstriae resembling fingerprint lines were observed in the flap in 48 eyes (13.87%), and epithelial ingrowth was seen in 23 eyes (6.65%) and two keratoectasia cases (0.58%). Some of these cases with microstriae and ingrowth, which affected the vision and/or corneal topography, underwent relifting and extending flaps.

3.6. Comparison between single treatment group and retreatment group

Next, samples were divided into two groups (single treatment group and retreatment one), and the data were analyzed for UCVA, BCVA, and manifest SE. The preoperative data and the postoperative course were summarized. Preoperative UCVA, BCVA, and manifest SE were not statistically different [Table 2]. Postoperative courses showed difference in UCVA and SE at some time points, but not in BCVA [Figure 11].
Table 2: Preoperative data for patients undergoing single and multiple surgeries.

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Figure 11: Postoperative time-course change in (A) uncorrected visual acuity, (B) bestcorrected visual acuity, and (C) spherical equivalent of the single treatment and retreatment groups.

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  4. Discussion Top


In this study, we have shown the 10-year outcomes of LASIK in myopia/myopic astigmatism patients performed in a single clinic.

Post-LASIK refractions were stable for a long time after the initial surgery, although minimal regression was observed. Myopic regression is a universal phenomenon following excimer laser correction.[14] Previous studies with <1 year of follow-up found an average regression rate ranging between −0.50 σ and −1.15 σ after laser correction of high myopia.[2],[5],[8],[15],[16],[17],[18],[19],[20],[21],[22] There are many reasons for myopic regression, including epithelial hyperplasia, corneal steepening, changes in corneal biomechanics, increases in axial length, and lenticular sclerosis.[14],[20],[21] Other studies have suggested that regression in high myopic eyes can occur because of flap creation and reduced structural corneal integrity, attributable to excessive ablation, which may lead to progressive corneal ectasia.[23] Alio et al implied that myopic regression increases with higher corrections.[11] Likewise, we found similar correlation, suggesting that myopic regression increased with higher corrections. Additionally, the mean age of patients included in the present study at 10 years was 44.9 years, and the natural history of age-related changes may need to be considered when assessing refractive stability.[24] In this Beaver Dam study, significant changes occurred in SE over a 10-year period in adults. Younger people became more hyperopic, whereas older people became more myopic. Severity of nuclear sclerosis was also strongly related to amount of change.[24]

Based on the Beaver Dam study, we can speculate that the early postoperative plateau period is due to the good balance between refractive regression and hyperopic shift in younger patients, and that later myopic shift is due to an additive effect of refractive regression and myopic shift in older patients. However, the age range of patients is different but overlapping (our study, 18–67 years; Beaver Dam study, 43–84 years).[24] Recent advances in laser profiles and technologies should be taken into account when comparing these results with those of more recent procedures.

Our overall retreatment rate was 35.8%, which was similar to that in previous reports of laser refractive surgery for myopia, with r-treatment rates between 30% and 40% after photorefractive ker-atectomy or LASIK.[2],[16],[17],[18],[19],[20],[21],[22] The main reason for retreatment was dissatisfaction with the visual result. Although it is not always easy to provide clear reasons for retreatments, in this study, reasons were classified as primary undercorrection in 17 (13.7%) of 124 eyes, and regression in 107 eyes (86.3%).

Interestingly, in a previous study, patients with moderate to high myopia underwent minimal retreatments over 7 years (0–0.5%). However, in this study, there was no symptomatic increase in myopic regression to warrant a higher retreatment rate in the high myopic group. In individuals with high myopia, the lower retreatment rates may be attributed to the lack of residual stroma; however, we are unable to confirm this. Another reason for the lower retreatment rates in high myopes may be patient satisfaction with a large improvement in refractive errors and functional vision.

The efficacy results of this study were inferior to those of the study based on the data submitted to the Food and Drug Administration (FDA),[25] which reported that 97% achieved a postoperative UCVA of 20/40, and 62% of the eyes achieved 20/20 UCVA (86.1% for 20/40 and 52.0% for 20/20 at 10 years in our study). However, our results are comparable to previous studies of LASIK for high myopia, which show that 46–78% of eyes achieved UCVA of 20/40 or better after 6 months of follow-up.2, 5, 8, 15–22

Regarding the visual outcomes, the safety index was good (0.99), which is comparable with the safety index of 1.08 in a large, long-term study.[11] The efficacy index was 0.71, which is inferior to 0.88 in a large, long-term study.[11]

We found that 76.3% of eyes were within ±1.00 σ and 95.7% were within ±2.00 σ, 10 years after LASIK. Our results are superior to those of previous short-term follow-up studies of LASIK for high myopia, which found that between 30% and 60% of eyes were within ±1.00 σ after surgery[2],[5],[8],[15],[16],[17],[18],[19],[20],[21],[22]; however, our results are inferior to the data from FDA trials, which show that 72% of eyes achieved a refractive error of 0.50 σ of the intended correction and 90% of eyes were within 1.00 σ of the target.[26]

We have to admit that our study had a critical problem: it included single-treatment as well as multiple-treatment cases. From a different point of view, however, we can conclude that with or without retreatment, our results present the true picture of the post-LASIK course. We believe this complexity may apply in clinical settings, because several patients understand the need for retreatment and would like to be aware of the long-time results with or without retreatments.

Regarding complications, our results were similar to those of previous reports.[27],[28],[29] In our study, the 15 eyes (4.6%) with loss of BCVA of two lines were possibly associated with the following: the progression of cataracts, keratoectasia, and epithelial impairment due to dry eye; however, we were unable to identify any obvious reason in several cases. There was a low rate of loss in BCVA in the FDA trials (from 1993 to 2002), with a range of 0% and 4.5% of eyes, losing two lines of BCVA.[26] Previous studies have shown that corneal ectasia usually develops in the first 2 years after LASIK, and identified high myopia, FFKC, low RBT, and multiple enhancements as risk factors for the development of ectasia.[30],[31] Accordingly, in our study, two eyes developed corneal ectasia detected at 1 year and 2 years after LASIK, respectively. These two eyes underwent LASIK for extremely high myopia (-15 σ and -11 σ), with planned postoperative total corneal thickness over 400 mm. Neither of these two cases had preoperative FFKC on the corneal topography. In the early cases at our clinic, we did not perform intraoperative pachy-metry measurement. Therefore, deviations from the mean depth of the microkeratome pass may have created thicker flaps with lower RBT than intended. We experienced two keratoectasia cases, and the rate (0.58%) is higher than that reported by Randleman et al (0.04%).[30]

The mean postoperative IOP dropped by 4.04 mmHg at 1 month and remained unchanged thereafter, consistent with previous reports.[32] We always emphasize to our patients the importance of receiving regular postoperative examinations up to 10 years; however, the frequency at which patients visited our institute for postoperative examinations was 94% at 1 week after surgery, 87% at 1 month, 73% at 3 months, 55% at 6 months, 46% at 1 year, 9.3% at 5 years; this percentage continued to decline thereafter.[9] This study indicated that the frequency of postoperative examination fell to 6.3% at 10 years after surgery. There are many reasons for not retuning for postoperative examinations. Some approached other institutes because of personal circumstances. However, the majority of patients simply disregarded our recommendation for follow-up examinations, probably because they felt there was no need for follow-up. Thus, it would seem that those who were satisfied with the results of the surgery tended to forget or ignore the schedule for postoperative examinations, whereas those who experienced irregularities in their visual performance frequently came back to the institute. Therefore, the true incidence of regression, enhancement, and patient satisfaction among all patients who undergo LASIK is likely to differ somewhat from what is reported in this study.

Although the relatively low 10-year visit rate (6.3%) may have biased the results, LASIK surgery can be considered an effective and safe procedure for the correction of myopia/myopic astigmatism as long as the inclusion and exclusion criteria are strictly respected and patients understand the pros and cons of this procedure. However, regular check-ups are recommended. During this 10-year study period, we have encountered many technical improvements, and we will continue to accumulate and analyze data as they correlate to these changes in technology and report them in a future study.

Conflicts of interest: The authors declare that they have no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11]
 
 
    Tables

  [Table 1], [Table 2]


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1 Factors Affecting Myopic Regression after Laser in Situ Keratomileusis and Laser-Assisted Subepithelial Keratectomy for High Myopia
Mingna Liu,Hua Gao,Weiyun Shi
Seminars in Ophthalmology. 2019; : 1
[Pubmed] | [DOI]



 

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