Ten-year Follow-up of Laser In Situ Keratomileusis for High Myopia

Patient Population 

The global study included 294 eyes of 178 patients treated with myopic LASIK at the Instituto Oftalmológico de Alicante, Spain between April 1, 1992 and December 31, 1995. The patients returned for follow-up at three months, one year, two years, five years, and 10 years after the initial procedure, either spontaneously or after telephone calls (particularly at 10 years). Among this group, 196 (106 right, 90 left) eyes of 118 consecutive patients who had a myopic spherical equivalent over −10 D with the information at each time gate or just at 10 years visit (availability of preoperative and postoperative topography maps at 10 years follow-up), were included in this study. No patients were excluded other than the ones who did not comply with the inclusion criteria.

Patient demographics and refraction at the time of treatment are given in Table 1. Inclusion criteria for surgery were: 1) no contact lens wear four weeks before the surgery and 2) stable refractive error for at least six months before surgery, normal peripheral retina or treated with photocoagulation when necessary, previous ocular surgery, corneal diseases, glaucoma, or history of ocular trauma. Informed consent was obtained from all patients after they received a detailed description of LASIK and a thorough review of its known risks. Exclusion criteria for surgery were: 1) evidence of keratoconus or 2) keratoconus suspect as evidenced by corneal topography, active ocular or systemic disease likely to affect corneal wound healing, pregnant, and nursing.

TABLE 1. Patient Demographics of the 196 Eyes Before LASIK for High Myopia

	Characteristics	Data
	Age (years)	32.9±9.3(18to58)
	Gender (patients)
	Male	52
	Female	66
	Sphere (D)	−13.10±2.83(−8.00to−24.00)
	Cylinder (D)	−1.70±1.09(0.00to−5.00)
	Spherical equivalent (D)	−13.95±2.79(−10.00to−24.50)

LASIK = laser in situ keratomileusis; D = diopters.

Surgical Procedure 

The day before surgery, diclofenac sodium 0.1% drops (Voltaren; Novartis AG, Basel, Switzerland) trimethoprim, and polymyxin B eye drops (Oftalmotrim; Cusi, Barcelona, Spain) were instilled. The procedure was done using topical anesthesia of oxybuprocaine 0.4%. All surgeries were performed by three surgeons (J.L.A., J.J.P.Z., A.A.) using the same technique and same protocol.13 A 8.5- to 9.0 mm diameter superiorly hinged anterior corneal flap was created in thickness using the Automated Corneal Shaper (ACS; Chiron Vision, Irvine, California, USA) microkeratome with either 130 or 160 μm head, in every patient.

A 193 nm VISX Twenty-Twenty excimer laser (VISX Inc, Santa Clara, California, USA) was used. Calibration was done at the beginning of each surgical session. During surgery, patients fixated on the laser’s helium–neon fixation light. Ablation was achieved using a beam with fluence of 160 mJ/ cm2 at an ablation rate of 5 Hz. A 4.5, 5, and 6.0 mm diameter multiple zone technique was used. Astigmatism was corrected by sequential ablation with an area of 6.0 x 4.5 mm. The mean optical zone was 5.88 ± 0.27 (range, 5.00 to 6.00 mm) and the mean ablation depth was 141 ± 24 (range, 94 to 214 μm). Emmetropia was attempted in most cases. However, in some cases, under correction (in eyes with inadequate corneal thickness [CT]) were intended.

Postoperatively, tobramycin (Tobrex; Alcon Laboratories, Inc, Fort Worth, Texas, USA) and diclofenac 0.1% drops (Basel, Switzerland) were used. Dexamethasone 0.1% was used four times a day during the first week. Subsequently, fluorometholone 0.25% was applied four times daily for a minimum of four weeks based on the refraction and intraocular pressure. The steroid dose was tapered gradually (three times and two times daily for two weeks each).

Retreatments 

The criteria for retreatment always included one of the following three parameters: 1) manifest spherical equivalent (SE) of −1.00 D or greater; 2) uncorrected visual acuity (UCVA) of 20/40 or less; and 3) patient dissatisfaction with the visual result. Under correction was defined as an SE of −1.00 D or greater at the first postoperative visit. Regression was noted when a 0.50 D or greater myopic shift occurred between follow-up visits without the presence of a retreatment.

LASIK retreatments were performed by lifting the flap and re-ablating the stromal bed. Before the surgery, the edge of the flap was marked with gentian violet on the temporal side. A flat spatula was used to lift the corneal flap. The stromal bed was then ablated using the one of the following: 1) VISX 20/20 excimer laser (49 retreatments), NIDEK EC-5000 (NIDEK Co, Gamagori, Japan; one retreatment), and 2) Technolas 217 (Bausch & Lomb, Rochester, New York, USA; four retreatments). After ablation, the flap was replaced to its original position, and the interface was irrigated copiously.

Postoperative Evaluation 

All patients were evaluated three months, one year, two years, five years, and 10 years after LASIK, including measurement of manifest refraction, cycloplegic refraction, UCVA, best spectacle-corrected visual acuity (BSCVA), slit-lamp biomicroscopy, dilated funduscopy, applanation tonometry, and CT using DGH-500 pachymeter (DGH Technology Inc, Exton, Pennsylvania, USA), or Alcon Ocuscan RxP Ophthalmic Ultrasound System (Alcon Laboratories, Inc). Visual acuity was measured using a standard Snellen acuity chart at 6 meters. All patients had corneal topography evaluated using EyeSys topographer (EyeSys Corneal Analysis System, Houston, Texas, USA; preoperative to five years of follow-up), Orbscan I slit-scanner (Bausch & Lomb; only at five or 10 years of follow-up), and CSO corneal topography system (CSO, Firenze, Italy; only at 10 years follow-up).

Residual stromal bed (RSB) was estimated by two methods: 1) preoperative pachymetry minus predicted flap thickness (according to Pérez-Santonja and associates, they found a mean flap thickness of 114 ± 17 μm for the 160 μm head and 88 ± 12 μm for the 130 μm head for the ACS microkeratome) minus calculated ablation depth, and 2) postoperative pachymetry (using the latest available pachymetry data) minus predicted flap thickness.13 If enhancement procedures were performed, the RSB was estimated using the sum of the calculated ablation depths for all procedures.

Patients were examined and evaluated by independent examiners at each follow-up. Data obtained at the end of 10 years and evaluated retrospectively regarding the format for reporting refractive surgical data,14, 15 and including the safety and efficacy indexes: Safety = (BCVApostoperative/BCVApreoperative); Efficacy = (UCVApostoperative/BCVApreoperative). Also, the results of eyes who underwent retreatment (retreatment group) and who did not undergo retreatment (no retreatmeant group) were compared.

Statistical Analysis 

Data analysis was performed using SPSS for Windows version 11.0 (SPSS Inc, Chicago, Illinois, USA). Normality was checked by the Kolmogorov–Smirnov test and normal probability plots. Mann–Whitney U test was performed to compare no retreatment and retreatment groups. Correlations were tested using the Spearman correlation coefficient. Differences were considered to be statistically significant when the P value was <.05.

Retreatments, Refractive Stability, and Predictability 

The scattergram of attempted vs achieved correction at three months (Left) and 10 years (Right) postoperatively are illustrated in Figure 1. Fifty-four (27.5%) of 196 eyes [41 of 118 patients] underwent retreatments: 52 eyes (96%) of 40 patients underwent only one retreatment, and two eyes (4%) of one patient underwent two retreatments. The indications for retreatment were under correction in 37 eyes (68%) of 27 patients, followed by regression in 14 eyes (26%) of 11 patients, and both overcorrection and regression in three eyes (6%) of three patients. Thirty-four of 23 patients underwent retreatment between three months and one-year follow-up, 12 eyes of nine patients between one year and two years follow-up, four eyes of four patients between two years and five years follow-up, and six eyes of five patients after five years follow-up.

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FIGURE 1. Scattergram of attempted vs achieved correction at three months (Left) and 10 years (Right) after laser in situ keratomileusis (LASIK) surgery for the 196 highly myopic eyes of our study. Retreatments were represented separately.

Postoperatively, the mean SE slightly decreased (myopic regression) over 10 years (Figure 2). The mean regression and regression per year are given in Table 2. Given that most of the retreatments were performed between three months and five-year follow-up, the regression rate in eyes that undergone retreatment were influenced by retreatments in this period. In eyes that did not undergo retreatment, the rate of regression per year slowed down during 10 years of follow-up. The correlation between regression per year vs age, preoperative SE, preoperative corneal power, attempted correction, achieved correction, change in corneal power, ablation depth, calculated RSB, postoperative RSB, and change in CT is demonstrated in Table 3.

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FIGURE 2. Mean value of the spherical equivalent (SE) preoperatively and three months, one, two, five, and 10 years after LASIK surgery for the 196 highly myopic eyes of our study. Primary procedures and retreatments were represented grouped together and separately. Error bars represent the standard deviation.

TABLE 2. Mean Values and Standard Deviation of Regression After LASIK for High Myopia

		All eyes (n = 196)	No retreatment (n =142)	Retreatment (n = 54)	P⁎
	Regression (D)
	3 mos to 10 years	−1.83±2.22	−2.46±1.80	−0.19±2.38	0.00†
	1 to 10 years	−1.61±2.21	−1.76±1.79	−1.20±3.04	0.06
	2 to 10 years	−1.24±1.88	−1.22±1.68	−1.29±2.33	0.46
	5 to 10 years	−0.69±1.72	−0.68±1.61	−0.72±2.01	0.82
	Regression per year (D/year)
	3 mos to 10 years	−0.18±0.22	−0.25±0.18	−0.02±0.24	0.00†
	1 to 10 years	−0.18±0.25	−0.19±0.20	−0.13±0.34	0.07
	3 mos to 1 year	−0.30±2.24	−0.93±1.42	1.35±3.03	0.00†
	1 to 2 years	−0.37±1.30	−0.54±1.09	0.09±1.66	0.17
	2 to 5 years	−0.18±0.36	−0.18±0.32	−0.19±0.43	0.74
	5 to 10 years	−0.14±0.34	−0.13±0.32	−0.14±0.40	0.84

SE = spherical equivalent; LASIK = laser in situ keratomileusis; D = diopters; mos = months; n = number of eyes.

⁎ Significance of difference between no retreatment and retreatment groups by Mann–Whitney U test. † Statistically significant.

TABLE 3. Correlation (The Spearman Coefficient) between Different Ocular Variables and the Regression Value After LASIK for High Myopia⁎

	Parameter	All eyes (n = 196)	No retreatment (n =142)	Retreatment (n = 54)
	Time period	2 to 10 years	3 mos to 10 years	2 to 10 years
	Age	0.13(0.08)	0.07(0.42)	0.33(0.02)†
	Preoperative SE	0.11(0.13)	0.17(0.04)†	0.28(0.04)†
	Preoperative C Power	−0.03(0.66)	−0.14(0.09)	0.02(0.90)
	Attempted correction	0.12(0.11)	0.18(0.04)†	0.24(0.08)
	Achieved correction	0.33(0.01)†	0.23(0.01)†	0.34(0.01)†
	Change in C power	0.01(0.85)	0.04(0.65)	0.07(0.64)
	Ablation depth	0.00(0.99)	0.02(0.84)	−0.17(0.24)
	Calculated RSB	0.07(0.36)	−0.07(0.44)	0.40(0.01)†
	Postoperative RSB	0.11(0.13)	0.09(0.28)	0.29(0.03)†
	Change in CT	0.04(0.57)	0.09(0.31)	0.14(0.32)

SE = spherical equivalent; C = corneal; LASIK = laser in situ keratomileusis; RSB = residual stromal bed; CT = corneal thickness.

⁎ All data are in the Spearman correlation coefficient (statistical significance). † Statistically significant.

The percentage of eyes within ±0.50 D, ±1.00 D, ±2.00 D emmetropia after 10 years is demonstrated in Figure 3.

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FIGURE 3. Percentage of eyes within ±0.50 diopter (D), ±1.00 D, ±2.00 D emmetropia (in terms of spherical equivalent) at 10 years after LASIK surgery for the 196 eyes globally and separating in eyes with and without retreatments.

Corneal Stability 

The mean corneal power slightly increased (0.74 D) between the three months and one-year period and remained stable after one year up to 10 years (Figure 4, Left). Also, a slight increase (0.32 D) in the mean topographical cylinder was observed over 10 years (Figure 4, Right).

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FIGURE 4. Corneal power (Left) and topographical cylinder (Right) preoperatively and three months, one, two, five, and 10 years after LASIK surgery for high myopia. Primary procedures and retreatments were represented grouped together and separately. Error bars represent the standard deviation.

Visual Outcome 

The safety index was 1.21 at 10 years. Figure 5 demonstrates the percentage of eyes that lost or gained Snellen lines (safety). Eleven eyes (5%) lost more than 2 lines of BSCVA at 10 years: Six eyes (3%) because of posterior segment related complications (myopic maculopathy: two eyes of one patient; retinal detachment: two eyes of two patients; neovascular membrane: two eyes of two patients), and four eyes (1.0%) of three patients because of cataract, and one eye (0.5%) of one patient because of corneal ectasia.

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FIGURE 5. Gained and lost lines of best spectacle-corrected visual acuity (BSCVA) at 10 years after LASIK surgery for the 196 highly myopic eyes (safety).

The efficacy index was 0.77 at 10 years. Figure 6 shows the preoperative BSCVA and postoperative UCVA percentage of eyes. The mean UCVA (Left) and BSCVA (Right) change over time is demonstrated in Figure 7.

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FIGURE 6. Cumulative distributions of preoperative BSCVA and postoperative uncorrected visual acuity (UCVA) of the 196 eyes 10 years after LASIK surgery for high myopia (Efficacy).

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FIGURE 7. Mean value of visual acuity preoperatively and three months, one, two, five, and 10 years after LASIK surgery for the 196 highly myopic eyes of our study. (Left) UCVA. (Right) BSCVA. Primary procedures and retreatments were represented grouped together and separately. Error bars represent the standard deviation.

Complications 

The complications seen after LASIK during 10 years of follow-up are given in Table 4. Postoperative haze or scarring in the stromal bed was minimal. Haze was never worse than mild throughout the follow-up. Two eyes (1%) of two patients developed corneal ectasia after LASIK:

TABLE 4. Incident of Complications After LASIK Surgery for High Myopia for each Follow-up Visit

		Number of eyes (%)
	Complications	3 months	1 year	2 years	5 years	10 years
	Surgical complications
	Epithelial ingrowth	0(0)	4(2.0)	5(2.6)	3(1.5)	2(1.0)
	Peripheral melting	0(0)	2(1.0)	3(1.5)	2(1.0)	2(1.0)
	Punctate keratopthy	4(2.0)	4(2.0)	3(1.5)	2(1.0)	1(0.5)
	Flap stria	2(1.0)	4(2.0)	3(1.5)	2(1.0)	2(1.0)
	Corneal ectasia	0(0)	1(0.5)	2(1.0)	2(1.0)	2(1.0)
	Complications related with myopia
	Cataract	0(0)	0(0)	1(0.5)	3(1.5)	7(3.6)
	Myopic maculopathy	1(0.5)	1(0.5)	1(0.5)	1(0.5)	4(2.0)
	RD or RD surgery	0(0)	0(0)	0(0)	1(0.5)	2(1.0)
	CNV	0(0)	0(0)	0(0)	0(0)	2(1.0)

CNV = choroidal neovascularization; LASIK = laser in situ keratomileusis; RD = retinal detachment.

Case 1 

A 24-year-old male underwent bilateral LASIK in 1995 with preoperative refractions of −8.00 −4.00 × 15 (SE, −10 D) in the right eye (OD) and −14.00 −5.00 × 170 (SE, −16.50 D) in the left eye (OS). Preoperative corneal topography was normal (no sign of forme-fruste keratoconus [FFKC]) with a symmetric bow-tie pattern (Simulated keratometry [SimK]1, 44 D; SimK2, 48.75 D). The preoperative CT was 558 μm OD and 558 μm OS. A 160-μm plate was used for the microkeratome cut and the planned ablation depth was 99 μm OD and 191 μm OS. The calculated RSB was 345 μm OD and 250 μm OS. The left eye developed corneal ectasia with significant inferior steepening on the corneal topography (SimK1, 38.25 D; SimK2, 46.0 D) six months after surgery without undergoing further enhancements. The postoperative CT at one year was 303 (RSB, 189 μm). The preoperative UCVA and BSCVA of the eye were counting fingers from 5 meters with significant myopic maculopathy. The postoperative visual acuity did not change significantly. Given the eye had posterior segment complication and no additional treatment was done. The fellow OD eye had a UCVA and BSCVA of 20/20 (preoperative BSCVA, 20/25) with + 0.50 − 0.25 × 45 refraction at 10 years.

Case 2 

A 48-year-old male underwent bilateral LASIK in 1996 with preoperative refractions of −18.50 −2.00 × 25 (SE, −19.5 D) in the right eye (OD) and −12.50 −2.00 × 165 (SE, −13.50 D) in the left eye (OS). Each eye had a BSCVA of 20/40. Preoperative corneal topography was normal (no sign of FFKC) with a symmetric bow-tie pattern (SimK1, 42.29 D; SimK2, 41.56 D). The preoperative CT was 560 μm OD and 575 μm OS. A 160-μm plate was used for the microkeratome cut and the planned ablation depth was 193 (calculated RSB, 253 μm) OD and 145 (calculated RSB, 316 μm) OS. At three months, both eyes had SE in ± 0.50 D but, both eyes underwent enhancements attributable to significant regressions after one-year follow-up (ablation depth, 38 μm OD and 21 μm OS). Two years after initial surgery, the right eye developed ectasia with significant inferior steepening on the corneal topography (K1, 34.50 D; K2, 38.0 D). The postoperative CT was 377 (calculated RSB, 245 μm) OD. At 10 years, the eye with ectasia had BSCVA of 20/200 with hard contact lens, and the fellow eye had a UCVA and BSCVA of 20/40, with a refraction of −0.50 × 130 D. The anterior segment optic coherence tomography (Visante OCT; Carl Zeiss Meditec, Dublin, California, USA) revealed a RSB of 127 μm and the ocular response analyzer (Reichert Ophthalmic Instruments, Depew, New York, USA) demonstrated a corneal resistance factor of 4.5 mm Hg (fellow eye 9 mm Hg) and a corneal hysteresis of 4.5 mm Hg (fellow eye 9 mm Hg) in the right eye.

Long-Term Refractive Predictability and Stability 

In this study, we have shown the long-term outcomes of high myopic patients 10 years after LASIK surgery. Nowadays, the LASIK surgery is not applied in patients within this refractive range (>10 D) and therefore this refractive correction supposes the maximum limit of application of this technique. We found that 42% of eyes were within ±1.00 D and 61% were within ±2.00 D, 10 years after LASIK. These rates were similar for the eyes that underwent retreatment and the eyes that did not. Our results are similar to those of previous short-term follow-up studies of LASIK for high myopia, that found that between 30% to 60% of eyes were within ±1.00 D after surgery.9, 10, 11, 12, 13, 16, 17, 18, 19, 20, 21, 22, 23

Some previous studies suggested that myopic ablations were accompanied by a hyperopic shift and the magnitude of the hyperopic shift increased with the magnitude of attempted correction.24, 25 Similar to the long-term studies of PRK for myopia, we could not observe a significant hyperopic shift after LASIK for high myopia.26, 27, 28 This could be attributable to our follow-up visits were starting from three months, therefore, if the hyperopic shift occurred in three months after LASIK, our study may have overlooked.

Myopic regression is a universal phenomena in eyes who undergone excimer laser correction for high myopia.29 Previous studies with less than one year of follow-up found an average regression rate ranging between −0.50 D to − 1.15 D after laser refractive correction of high myopia.9, 10, 11, 12, 13, 16, 17, 18, 19, 20, 21, 22, 23 In the present study, we observed an average myopic regression of −2.46 ± 1.80 D in 142 eyes who did not undergo retreatment, during 10 years of follow-up. We also found a mean regression rate of −0.25 ± 0.18 D per year for the no retreatment group. However, this rate gradually decreased from −0.93 ± 0.20 D per year between three months and one year to −0.13 ± 0.32 D per year between five and 10 years. Our data suggest that myopic regression stabilizes between two to five years after LASIK for high myopia. Many reasons may lead to myopic regression such as epithelial hyperplasia, corneal steepening because of corneal thinning, change in corneal biomechanics, increase in axial length, and lenticular sclerosis.29 In our study, we found a significant correlation between the myopic regression and the achieved correction, which implies that myopic regression increases with higher achieved corrections. Besides, the mean age of the present cohort of patients at 10 years was 42.9 years, thus, the natural history of age-related refractive changes needs to be considered when assessing refractive stability.30

Corneal Stability 

Other studies suggested that progressive 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.31 From the topographic standpoint, the mean corneal power demonstrated an increase of 1.2 D (no retreatment group) and the mean corneal cylinder remained relatively stable up to 10 years. Many studies showed that topography map (corneal power) underestimates achieved correction about 30% after myopic laser refractive surgery, greater in cases of higher corrections.32, 33, 34 The increase in corneal power seems to explain some part, but not all, of the myopic regression observed in our study, but we could not find significant correlations between regression vs ablation depth, change in CT, and RSB. Moreover, CT seemed to remain stable during 10 years of follow-up. These observations may infer that regression attributable to chronic stromal remodeling leading to corneal ectasia is a less likely event after LASIK for moderate myopia.

Retreatments 

Our retreatment rate was 30%, which was similar to the previous reports of laser refractive surgery for high myopes that found a retreatment rate between 30% to 40% after PRK or LASIK for high myopia.13, 16, 17, 18, 19, 20, 21, 22, 23 Although it is not always easy to define a clear cut, the reasons for retreatments were under correction in 37 (68%) of 54 eyes, followed by regression in 14 eyes (26%), and both over correction and regression in three eyes (6%). In our study, retreatments were safe and did not increase the rate of regression compared with the eyes that had no retreatment. In addition, we could not find significant difference in corneal power and topographical cylinder at 10 years between eyes that underwent retreatment and eyes that did not undergo retreatment.

Visual Outcome 

Regarding the visual outcomes, the safety score of our patients was very good (1.21) and the efficacy index was 0.77. The high improvement rate in BSCVA in eyes who underwent LASIK for high myopia may be explained by an increase in the size of the image on the macula.35, 36 Previous studies of LASIK (laser refractive surgery) for high myopia found that between 46% to 78% of eyes achieve UCVA of 20/40 or better after six months of follow-up.9, 10, 11, 12, 13, 16, 17, 18, 19, 20, 21, 22, 23 Slightly lower postoperative UCVA in our study seems to be related to myopic regression and to, some extent, under correction. Improvements in the nomograms regarding under correction and myopic regression have lead now to a better efficacy after LASIK for high myopia.

The UCVA and BSCVA showed good stability during follow-up (Figure 7). We observed an increase in UCVA between three months and five years, which seems to be partly attributable to the retreatments. However, there was a slight decrease in UCVA after five years, possibly attributable to slight regression, increase in lenticular sclerosis and myopic maculopathy. On the other hand, we observed a slight but gradual increase in BSCVA over the 10 years follow-up, despite eyes that demonstrated BSCVA loss because of lenticular sclerosis and posterior segment related complications.

Late Complications 

Previous studies demonstrated that corneal ectasia usually develops in the first two years after LASIK and identified high myopia, FFKC, low RSB, and multiple enhancements as risk factors for the development of ectasia.37, 38 Accordingly, in our study, two eyes developed corneal ectasia that was detected six months and two years after LASIK, respectively. These two eyes underwent LASIK for myopia over −15 D (−16.5 D and −19.5 D), with programmed ablation depth of 193 μm (calculated RSB, 250 μm) and 231 μm (calculated RSB together with enhancement, 231 μm). Neither of these two eyes had preoperative FFKC on the topography, but one of two eyes underwent retreatment attributable to significant myopic regression. Postoperatively, these eyes were found to have RSB of less than 200 μm (114 μm and 195 μm). Deviations from mean depth of microkeratome pass and deeper ablation than the programmed ablation may explain why these eyes had lower RSB than expected,13, 39 In our study, only five (2.6%) of 190 eyes had postoperative RSB less than 250 μm, and the other than ectasia cases demonstrated good visual outcomes. This may suggest that high myopia simply predisposes one to a thinner RSB rather than independently increasing the risk for developing ectasia.37

Keratoconus is a progressive disorder and the reported frequencies of unilateral keratoconus range from 0.5% to 4%.40 In a longitudinal study, approximately 50% of clinically normal fellow eyes were found to progress to keratoconus within 16 years, with a greatest risk during the first six years.41 Despite ectasia cases underwent bilateral LASIK for high myopia in our study, fellow eyes obtained a good refractive result after LASIK and remained stable during 10 years. This implies that subclinical keratoconus is a less likely cause of ectasia in these eyes.

Haze or scarring in the interface was minimal or absent after LASIK. Complications such as wrinkles in the flap and dot remnants in the interface were rare and should be avoided by using proper surgical technique. Although epithelial ingrowth in the interface was rare and usually did not progress, it seems to be a risk factor for flap melting. Flap melting usually developed on an epithelial ingrowth area and did not progress or progressed very slowly. It progressed more rapidly in one eye, although BSCVA did not decrease more than 2 lines in any case.

Significant late phase complications only occurred in limited number of eyes. Eight eyes (4%) (four eyes developed myopic maculopathy, two eyes retinal detachment, and two eyes choroidal neovascular membrane) developed high myopia related posterior segment complications which was not attributable to the LASIK procedure itself, but rather due to the myopic nature of the patient’s eye.42 Seven eyes (3.6%) developed significant nuclear sclerosis which was also not related to the LASIK procedure as it is well-documented that the rate of nuclear sclerosis is higher in high myopic eyes.43

In conclusion, our findings showed that LASIK for myopia over −10 D is a safe and effective procedure in the long-term with a high rate of BSCVA increase. Only 5% of eyes lost more than 2 lines of BSCVA and 40% of eyes avoided the use of glasses. Myopic regression positively correlates with the magnitude of achieved correction and its rate seems to slow down with time. Retreatments for under correction and/or regression seem to be safe and do not increase the rate of regression. These results are quite good, the contrary of we could expect at the beginning of the study, considering that this refractive correction supposes the maximum limit of application of this technique. Recent advances in corneal profiles and technologies should be taken into account when comparing these results with those of more recent procedures. Further long-term studies using advanced excimer laser algorithms and cornea analyzing systems are needed to evaluate the corneal biomechanical response and myopic regression after LASIK.