Journal of Refractive Surgery

Original Article 

Outcomes of Small Incision Lenticule Extraction (SMILE) in Low Myopia

Dan Z. Reinstein, MD, MA(Cantab), FRCOphth; Glenn I. Carp, MBBCh, FCOphth (SA); Timothy J. Archer, MA(Oxon), DipCompSci(Cantab); Marine Gobbe, MSTOptom, PhD

Abstract

Click here to read Letter to the Editor about this article

This article has been amended to include a factual correction. To read the erratum, click here. The online article and its erratum are considered the version of record.

PURPOSE:

To report the visual and refractive outcomes of small incision lenticule extraction for low myopia using the VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany).

METHODS:

A retrospective analysis of 120 consecutive small incision lenticule extraction procedures was performed for low myopia. Inclusion criteria were preoperative spherical equivalent refraction up to −3.50 diopters (D), cylinder up to 1.50 D, and corrected distance visual acuity of 20/20 or better. Outcomes analysis was performed for all eyes with 1-year follow-up according to the Standard Graphs for Reporting Refractive Surgery, and also including mesopic contrast sensitivity.

RESULTS:

One-year data were available for 110 eyes (92%). Preoperatively, mean spherical equivalent refraction was −2.61 ± 0.54 D (range: −1.03 to −3.50 D) and mean cylinder was 0.55 ± 0.38 D (range: 0.00 to 1.50 D). Postoperatively, mean spherical equivalent refraction was −0.05 ± 0.36 D (range: −0.94 to +1.25 D) and mean cylinder was ±0.50 D in 84% and ±1.00 D in 99% of eyes. Uncorrected distance visual acuity was 20/20 or better in 96% of eyes and 20/25 or better in 100% of eyes. One line of corrected distance visual acuity was lost in 9%, but no eyes lost two or more lines. There was an initial overcorrection in mean spherical equivalent refraction on day 1 (+0.37 D) as expected, which regressed to +0.10 D at 1 month and −0.05 D at 3 months, after which stability was reached (mean spherical equivalent refraction was −0.05 D at 1 year). Contrast sensitivity at 1 year was slightly increased at 3, 6, 12, and 18 cycles per degree (P < .05).

CONCLUSIONS:

Small incision lenticule extraction for low myopia was found to be safe and effective with outcomes similar to those previously reported for LASIK.

[J Refract Surg. 2014;30(12):812–818.]

From London Vision Clinic, London, United Kingdom (DZR, GIC, TJA, MG); the Department of Ophthalmology, Columbia University Medical Center, New York, New York (DZR); and Centre Hospitalier National d’Ophtalmologie, Paris, France (DZR).

Dr. Reinstein is a consultant for Carl Zeiss Meditec (Jena, Germany) and has a proprietary interest in the Artemis technology (ArcScan, Inc., Morrison, CO) through patents administered by the Cornell Center for Technology Enterprise and Commercialization (Ithaca, NY). The remaining authors have no financial or proprietary interest in the materials presented herein.

AUTHOR CONTRIBUTIONS

Study concept and design (GIC, TJA, MG, DZR); data collection (GIC, TJA, MG, DZR); analysis and interpretation of data (GIC, TJA, MG, DZR); drafting of the manuscript (TJA, DZR); critical revision of the manuscript (GIC, MG); statistical expertise (TJA, DZR)

Correspondence: Dan Z. Reinstein, MD, MA(Cantab), FRCOphth, London Vision Clinic, 138 Harley Street, London W1G 7LA, United Kingdom. E-mail: dzr@londonvisionclinic.com

Received: September 30, 2014
Accepted: October 14, 2014

Abstract

Click here to read Letter to the Editor about this article

This article has been amended to include a factual correction. To read the erratum, click here. The online article and its erratum are considered the version of record.

PURPOSE:

To report the visual and refractive outcomes of small incision lenticule extraction for low myopia using the VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany).

METHODS:

A retrospective analysis of 120 consecutive small incision lenticule extraction procedures was performed for low myopia. Inclusion criteria were preoperative spherical equivalent refraction up to −3.50 diopters (D), cylinder up to 1.50 D, and corrected distance visual acuity of 20/20 or better. Outcomes analysis was performed for all eyes with 1-year follow-up according to the Standard Graphs for Reporting Refractive Surgery, and also including mesopic contrast sensitivity.

RESULTS:

One-year data were available for 110 eyes (92%). Preoperatively, mean spherical equivalent refraction was −2.61 ± 0.54 D (range: −1.03 to −3.50 D) and mean cylinder was 0.55 ± 0.38 D (range: 0.00 to 1.50 D). Postoperatively, mean spherical equivalent refraction was −0.05 ± 0.36 D (range: −0.94 to +1.25 D) and mean cylinder was ±0.50 D in 84% and ±1.00 D in 99% of eyes. Uncorrected distance visual acuity was 20/20 or better in 96% of eyes and 20/25 or better in 100% of eyes. One line of corrected distance visual acuity was lost in 9%, but no eyes lost two or more lines. There was an initial overcorrection in mean spherical equivalent refraction on day 1 (+0.37 D) as expected, which regressed to +0.10 D at 1 month and −0.05 D at 3 months, after which stability was reached (mean spherical equivalent refraction was −0.05 D at 1 year). Contrast sensitivity at 1 year was slightly increased at 3, 6, 12, and 18 cycles per degree (P < .05).

CONCLUSIONS:

Small incision lenticule extraction for low myopia was found to be safe and effective with outcomes similar to those previously reported for LASIK.

[J Refract Surg. 2014;30(12):812–818.]

From London Vision Clinic, London, United Kingdom (DZR, GIC, TJA, MG); the Department of Ophthalmology, Columbia University Medical Center, New York, New York (DZR); and Centre Hospitalier National d’Ophtalmologie, Paris, France (DZR).

Dr. Reinstein is a consultant for Carl Zeiss Meditec (Jena, Germany) and has a proprietary interest in the Artemis technology (ArcScan, Inc., Morrison, CO) through patents administered by the Cornell Center for Technology Enterprise and Commercialization (Ithaca, NY). The remaining authors have no financial or proprietary interest in the materials presented herein.

AUTHOR CONTRIBUTIONS

Study concept and design (GIC, TJA, MG, DZR); data collection (GIC, TJA, MG, DZR); analysis and interpretation of data (GIC, TJA, MG, DZR); drafting of the manuscript (TJA, DZR); critical revision of the manuscript (GIC, MG); statistical expertise (TJA, DZR)

Correspondence: Dan Z. Reinstein, MD, MA(Cantab), FRCOphth, London Vision Clinic, 138 Harley Street, London W1G 7LA, United Kingdom. E-mail: dzr@londonvisionclinic.com

Received: September 30, 2014
Accepted: October 14, 2014

Small incision lenticule extraction (SMILE) was introduced in 2011 using the VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany)1,2 and studies reporting the outcomes of the procedure have been published for myopia up to −11.50 diopters (D).1–9 However, only a small proportion of eyes (6%) included in these studies addressed the outcomes for low myopia (≤ −3.50 D). This is partly due to the fact that most eyes were treated by Hjortdal et al., who have mainly treated higher myopia due to government subsidies for refractive surgery for high myopia.3 The CE Marked approved range of treatment for SMILE using the VisuMax femtosecond laser is from −0.01 to −10.00 D. However, until now, SMILE has generally been used more for moderate and high myopia.

The current study aims to report on the efficacy and safety, including contrast sensitivity changes, for SMILE treatment of low myopia using the VisuMax femtosecond laser in a large population.

Patients and Methods

This was a retrospective non-comparative case series of 120 consecutive low myopic SMILE procedures performed by two surgeons (DZR, GIC) using the VisuMax femtosecond laser at the London Vision Clinic. The analysis included all eyes with an attempted manifest spherical equivalent refraction up to −3.50 D, cylinder up to 1.50 D, corrected distance visual acuity of 20/20 or better, and age younger than 42 years. Because this was a retrospective study, only informed consent and permission to use their data for analysis and publication was obtained from each patient as part of our routine preoperative protocol.

Preoperative Assessment

All patients were evaluated according to the standard protocol for corneal refractive surgery assessment of the London Vision Clinic, which includes a full ophthalmologic examination performed by one of our in-house optometrists.10 Specifically, manifest refraction was performed based on a standardized refraction protocol11 and all optometrists and surgeons had undergone refraction training and validation with this protocol.12 The manifest refraction was performed at the initial visit as part of the ophthalmic examination and repeated at a separate visit before the day of surgery by the surgeon who determined the final refraction to plan the treatment.

Surgical Protocol

All SMILE treatments were performed using the VisuMax 500-kHz femtosecond laser (software version 2.4.0; Carl Zeiss Meditec) as described in detail previously.1–3,13 Details of the geometry and software set-up of the SMILE lenticule, cap, and small incision have been described previously.1–3,14–16 In the current study, two incisions were created in all eyes: a 2-mm incision superonasally and a 2-mm incision superotemporally. The small size contact glass was used for all eyes. The cap thickness used was between 120 and 160 μm, with 79% in the range of 130 to 140 μm. The optical zone diameter used was between 6.00 and 7.50 mm. The minimum lenticule thickness used was 3 to 5 μm in 2 eyes (2%), 10 μm in 63 eyes (53%), 15 μm in 28 eyes (23%), 20 μm in 24 eyes (20%), and 25 μm in 3 eyes (3%). To maximize the ease of separating the two planes, the thickness of the lenticule was deliberately increased by increasing the optical zone, transition zone, and minimum lenticule thickness. The spot and track distance were 4.6 μm for the cap and lenticule interfaces, 1.5 μm for the lenticule side cut, and 2.0 μm for the small incision. A personalized nomogram was applied to all treatments based on our early experience with SMILE and was used to calculate the laser data entry; the same nomogram was used for both surgeons.

The femtosecond laser cutting was performed as described previously.1–3,16 Total femtosecond ablation time was approximately 30 seconds, independent of refractive error treated, with a total suction time of approximately 35 seconds.

The 2-mm superotemporal incision was opened and the upper and lower planes of the lenticule edge were delineated. If it was not possible to delineate the edge of both interfaces, the second 2-mm superonasal incision was opened to find the edge that had yet to be delineated (usually the lower plane). The upper interface was separated first using a standard lamellar corneal surgical technique, taking care to avoid distension of the overlying stromal cap. The lower lenticular interface was then separated in a similar fashion. Once both planes had been separated, the lenticule was removed from the cornea by pushing the lenticule out through one of the two small incisions. The lenticule was then hydrated with balanced salt solution on the corneal surface to distend it for visual inspection for completeness and edge smoothness.

On completion of SMILE in both eyes, the patient was brought to the operating room slit lamp, fluorescein was instilled, and full central distention of the cap was achieved by centrifugal stroking using a dry micro-spear to ensure that any redundant cap (due to mismatch of cap vs bed length) was redistributed to the periphery.

The target postoperative sphere was hyperopic for all patients younger than 42 years. A linear function was used for the target hyperopia with a target sphere of +0.75 D for a 21-year-old patient, decreasing linearly to plano for a 42-year-old patient.

Postoperative Evaluation

Patients were instructed to wear plastic shields while sleeping for 7 nights. Tobramycin and dexamethasone (Tobradex; Alcon Laboratories, Inc., Fort Worth, TX) and ofloxacin (Exocin; Allergan Ltd., Marlow, United Kingdom) were applied four times daily for the first week, which is our standard protocol for broad-spectrum prophylaxis. All patients at the London Vision Clinic are routinely reviewed at 1 day and 1, 3, and 12 months. All follow-up visits routinely include measurement of monocular and binocular uncorrected distance visual acuity. A spherical refraction is routinely obtained at the 1-day appointment for all patients. Manifest refraction and corrected distance visual acuity are routinely obtained at all other postoperative visits. Best-corrected mesopic contrast sensitivity is routinely tested on all patients at the 3- and 12-month visits. One-day postoperative examinations are routinely conducted by the surgeons (DZR, GIC), at which point the cap may be adjusted at the slit lamp using a surgical spear if any microfolds are identified. All other postoperative examinations are routinely conducted by one of seven in-house optometrists.

Postoperative complications including microfolds, diffuse lamellar keratitis, infection, interface debris, transient light sensitivity, epithelial ingrowth, and interface haze were assessed at each visit using a 6 grade classification system: trace, grades I to II (not visually significant), grades III to V (visually significant). Data for these complications were reported for the 3-month postoperative visit.

Statistical Analysis

Outcome analysis was performed according to the Standard Graphs for Reporting Refractive Surgery.17–20 The outcomes were analyzed for the primary treatment data, excluding re-treatments. Data from the 1-year visit was used for analysis and eyes with less than 1-year data were excluded from the analysis as lost to follow-up. All eyes were included for intraoperative and postoperative complications analysis. Mesopic contrast sensitivity data were converted into log values before calculating statistics. The mean normalized mesopic contrast sensitivity ratio was calculated.21 Student’s t tests were used to evaluate the change in mesopic contrast sensitivity.

Microsoft Excel 2010 (Microsoft Corp., Redmond, WA) was used for data entry and statistical analysis. A P value less than .05 was defined as statistically significant.

Results

One-year data were available for 110 (92%) of 120 eyes. Table 1 shows descriptive statistics for the eyes treated. The lenticule and cap parameters are also provided in Table 1. The standard graphs are shown in Figure 1. Uncorrected distance visual acuity at 1 day, 1 and 3 months, and 1 year is presented in Figure 2. Table 2 presents the normalized mesopic contrast sensitivity data.

Demographic and Refractive Data

Table 1:

Demographic and Refractive Data

Figure 1. Nine standard graphs for reporting refractive surgery showing the visual and refractive outcomes for 110 eyes with low myopia treated with small incision lenticule extraction using the VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany). UDVA = uncorrected distance visual acuity; CDVA= corrected distance visual acuity; D = diopters; Postop = postoperative; Preop = preoperative; SEQ = spherical equivalent refraction; TIA = target induced astigmatism; SIA = surgically induced astigmatism

Cumulative histogram for uncorrected distance visual acuity (UDVA) at 1 day, 1 and 3 months, and 1 year.

Figure 2.

Cumulative histogram for uncorrected distance visual acuity (UDVA) at 1 day, 1 and 3 months, and 1 year.

Mean Normalized Mesopic Contrast Sensitivity Ratio for Before and After the Primary Treatment

Table 2:

Mean Normalized Mesopic Contrast Sensitivity Ratio for Before and After the Primary Treatment

Table 3 summarizes the intraoperative complications. There was one case of incomplete femtosecond laser cutting within a small central area of the cap, which was manually delicately dissected without compromise to the outcome (no change in corrected distance visual acuity or contrast sensitivity). There was one eye where a small tear-extension of the 2-mm incision occurred during the dissection phase of the lenticule, which healed normally without sequela.

Summary of Intraoperative Complications

Table 3:

Summary of Intraoperative Complications

One eye of another patient initially programmed for a −2.25 −0.25 × 8 treatment at a cap thickness of 160 μm resulted in the surgeon aborting the femtosecond laser cutting after creation of the deeper lenticular interface and lenticule side cut only when he noticed that the side cut was displaced from the lenticule edge by 1 mm; this was due to inadequate corneal immobilization as a result of a strong Bell’s reflex. The treatment was performed next on the second eye, without complication, to allow time for the minimal opaque bubble layer created in the first eye to dissipate. The treatment of the first (aborted) eye was re-attempted next. Because the intended cap thickness was initially 160 μm and the cap interface had not been started, the second treatment was re-programmed with a 135-μm cap thickness, thus leaving a 25-μm gap between the lower lenticule interface and the interface created in the first attempt, to effectively eliminate the probability of crossing interfaces; given the 4.4-μm reproducibility of the VisuMax 500 kHz femtosecond laser,14 the first interface could have been three standard deviations or 13.2 μm (= 3 × 4.4) shallower than intended and the lenticular interface of the second treatment could have been three standard deviations or 13.2 μm deeper than intended. The second lenticule was separated without difficulty and verified as whole. There was no change in corrected distance visual acuity or contrast sensitivity postoperatively.

Table 4 summarizes the postoperative complications at the 3-month visit. There were no visually significant complications. At the 1-month visit, 5 patients were prescribed fluorometholone 0.1% (Allergan, Ltd.) four times a day for 2 weeks for mild transient light sensitivity detected on direct questioning, with no cases of transient light sensitivity reported as a complaint by the patients themselves.

Summary of Postoperative Complications at the 3-Month Visita

Table 4:

Summary of Postoperative Complications at the 3-Month Visit

Re-treatments were performed once stability had been demonstrated, defined as a change in spherical equivalent refraction within ±0.25 D between time periods 3 months apart. To date, a re-treatment has been performed for 5 eyes (4%), all of which have been done using thin flap LASIK with the flap thickness chosen based on the 4.4-μm precision of the VisuMax femtosecond laser as calculated above to avoid crossing either the physiologically thickened epithelium or the primary SMILE interface.

Discussion

In the current study, SMILE for low myopic corrections has been shown to be safe and effective with a low rate of both intraoperative and postoperative complications. This study has shown that there are no concerns over the cutting accuracy of the VisuMax femtosecond laser for thinner lenticules, as has been previously demonstrated in terms of cap thickness reproducibility reported by various pachymetric methods as 4.4,14 5.1,22 5.2,23 and 9.0 μm.24

To compare these results to LASIK, we reviewed the peer-reviewed literature to find studies reporting the outcomes of LASIK for low myopia,25 as well as reviewing the U.S. Food and Drug Administration pre-market approval studies since 2002.26–31 We were only able to find one peer-reviewed article specifically about low myopic corrections and no studies after 2007. However, U.S. Food and Drug Administration studies provide a robust benchmark for modern LASIK outcomes and there have been effectively no changes to low myopic LASIK since 2007. The results are summarized in Table 5 and demonstrate that the outcomes of SMILE for low myopia are comparable to those achieved by LASIK.

Comparison of Outcomes for Low Myopic Corrections Between SMILE and LASIK

Table 5:

Comparison of Outcomes for Low Myopic Corrections Between SMILE and LASIK

One area where there is currently a difference between LASIK and SMILE is in the rate of visual recovery. The visual recovery (ie, day-1 vision) is slightly slower after SMILE compared to LASIK,4 although significant improvements have been made in this area by using different energy and spot spacing settings.32 The visual recovery in the current study was reasonably good, with 89% of eyes achieving 20/20 or better on day 1 compared to 91% by 1 month and 96% by 3 months.

Suction loss is potentially a significant complication in respect of being able to complete the procedure (there is no reason for a suction loss per se to detrimentally affect the vision if no dissection is performed). Our rate of suction loss with the VisuMax femtosecond laser has reduced over time due to adjustments implemented by the manufacturer, including increased suction pressure and suction port dimensions, and increasing the laser’s pulse repetition rate from 200 to 500 kHz (halving the suction time required). This is demonstrated by the 0.8% suction loss rate in the current study compared to 1.5% that we reported during the first cases treated with the VisuMax femtosecond laser.33 This rate of 0.8% is also the same as that reported for a large population by Ivarsen et al.34 Management of suction loss cases depends on when the suction loss occurs during the cutting sequence. If, as in the current study, the suction loss occurs during the creation of the lower lenticule interface or the lenticule side cut, then it is possible to simply reprogram the case with a thinner cap thickness (allowing safe limits between the lower lenticule interface and the aborted interface) and perform the procedure after the femtosecond laser bubbles have dissipated. If the suction loss occurs during the cap interface creation, then SMILE could be aborted and the eye switched to thin-flap LASIK, again programmed for the flap interface to avoid crossing whatever planes had been already created before the suction loss of SMILE.

SMILE for low myopia appears to be as effective and safe as LASIK. Although the early visual recovery is slightly slower for SMILE, this should be considered in the context of the relative advantages of a flapless procedure that avoids the various issues that can arise as a result of flap creation, repositioning, and healing, in particular the relative side effects and symptoms of dry eye related to the reestablishing of the anterior corneal nerve plexus35 and the potential biomechanical advantages related to leaving the stronger anterior stroma intact.36

References

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  12. Reinstein DZ, Yap TE, Carp GI, Archer TJ, Gobbe MLondon Vision Clinic Optometric Group. Reproducibility of manifest refraction between surgeons and optometrists in a clinical refractive surgery practice. J Cataract Refract Surg. 2014;40:450–459. doi:10.1016/j.jcrs.2013.08.053 [CrossRef]
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  16. Reinstein DZ, Archer TJ, Gobbe M. Small incision lenticule extraction (SMILE) history, fundamentals of a new refractive surgery technique and clinical outcomes. Eye and Vision. In press.
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  24. Vestergaard AH, Grauslund J, Ivarsen AR, Hjortdal JO. Central corneal sublayer pachymetry and biomechanical properties after refractive femtosecond lenticule extraction. J Refract Surg. 2014;30:102–108. doi:10.3928/1081597X-20140120-05 [CrossRef]
  25. de Benito-Llopis L, Teus MA, Sanchez-Pina JM, Hernandez-Verdejo JL. Comparison between LASEK and LASIK for the correction of low myopia. J Refract Surg. 2007;23:139–145.
  26. U.S. Food and Drug Administration. MEL 80 Excimer Laser System (PMA). Available at: http://www.accessdata.fda.gov/cdrh_docs/pdf6/P060004b.pdf. Accessed September 28, 2014.
  27. U.S. Food and Drug Administration. WaveLight ALLEGRETTO WAVE Excimer Laser System (PMA). Available at: http://www.accessdata.fda.gov/cdrh_docs/pdf3/P030008b.pdf. Accessed September 28, 2014.
  28. U.S. Food and Drug Administration. VISX STAR S4 IRTM Excimer Laser System with Variable Spot Scanning and WaveScan WaveFront System (Monovision) (PMA). Available at: http://www.accessdata.fda.gov/cdrh_docs/pdf/P930016s025b.pdf. Accessed September 28, 2014.
  29. U.S. Food and Drug Administration. Bausch & Lomb TECHNOLAS® 217z Zyoptix System for Personalized Vision Correction (PMA). Available at: http://www.accessdata.fda.gov/cdrh_docs/pdf/P990027S006b.pdf. Accessed September 28, 2014.
  30. U.S. Food and Drug Administration. LADARVision 4000 Excimer Laser System (PMA). Available at: http://www.accessdata.fda.gov/cdrh_docs/pdf/P970043S010b.pdf. Accessed September 28, 2014.
  31. U.S. Food and Drug Administration. STAR S4 Active Trak Excimer Laser System and WaveScan Wave Front System (PMA). Available at: http://www.accessdata.fda.gov/cdrh_docs/pdf/P930016S016b.pdf. Accessed September 28, 2014.
  32. Shah R, Shah S. Effect of scanning patterns on the results of femtosecond laser lenticule extraction refractive surgery. J Cataract Refract Surg. 2011;37:1636–1647. doi:10.1016/j.jcrs.2011.03.056 [CrossRef]
  33. Reinstein DZ, Carp GI, Archer TJ, Gobbe M. Transitioning from mechanical microkeratome to femtosecond flap creation: comparing experienced vs novice LASIK surgeon visual outcomes for the first 200 myopic procedures. J Cataract Refract Surg. 2012;38:1788–1795. doi:10.1016/j.jcrs.2012.05.038 [CrossRef]
  34. Ivarsen A, Asp S, Hjortdal J. Safety and complications of more than 1500 small-incision lenticule extraction procedures. Ophthalmology. 2014;121:822–828. doi:10.1016/j.ophtha.2013.11.006 [CrossRef]
  35. Li M, Zhao J, Shen Y, et al. Comparison of dry eye and corneal sensitivity between small incision lenticule extraction and femtosecond LASIK for myopia. PLoS One. 2013;8:e77797. doi:10.1371/journal.pone.0077797 [CrossRef]
  36. Reinstein DZ, Archer TJ, Randleman JB. Mathematical model to compare the relative tensile strength of the cornea after PRK, LASIK, and small incision lenticule extraction. J Refract Surg. 2013;29:454–460. doi:10.3928/1081597X-20130617-03 [CrossRef]

Demographic and Refractive Data

Parameter Mean ± SD (Range)
No. of eyes 110
No. of patients 69
Gender (male/female) (%) 54/46
Age (y) 32.4 ± 5.7 (range: 21 to 42)
Surgeon (DZR/GIC) (%) 61/39
Attempted SE refraction correction in primary treatment (D) −2.61 ± 0.54 (range: −1.03 to −3.50)
Preoperative refractive astigmatism (D) −0.55 ± 0.38 (range: 0.00 to −1.50)
SE refraction relative to intended target after primary treatment (D) −0.05 ± 0.36 (range: −0.94 to +1.25)
Refractive astigmatism after primary treatment (D) −0.20 ± 0.22 (range: 0.00 to −1.00)
Preoperative corneal thickness (μm) 544 ± 29 (range: 458 to 612)
Scotopic pupil size (mm) 5.52 ± 0.95 (range: 2.99 to 7.80)
Preoperative average keratometry (D) 43.20 ± 1.29 (range: 39.91 to 46.19)
SMILE cap thickness (μm) 136 ± 7 (range: 120 to 160)
SMILE lenticule thickness (μm) 79 ± 12 (range: 51 to 108)
SMILE minimum lenticule thickness (μm) 13 ± 5 (range: 3 to 25)
Optical zone (mm) 7.01 ± 0.25 (range: 6.00 to 7.50)

Mean Normalized Mesopic Contrast Sensitivity Ratio for Before and After the Primary Treatment

CPD Preoperative Postoperative Pa
3 1.00 1.03 .005
6 0.97 0.99 .007
12 0.98 1.01 .004
18 0.95 0.99 .008

Summary of Intraoperative Complications

Parameter Percentage (No. of Patients)
Epithelial defect within cap (BCL required) 4.2% (5/120)
Epithelial defect within cap (no BCL) 2.5% (3/120)
Epithelial defect at small incision (BCL required) 5.0% (6/120)
Epithelial defect at small incision (no BCL) 0.8% (1/120)
Suction loss 0.8% (1/120)
Incomplete femtosecond ablation 0.8% (1/120)
Incision extension 0.8% (1/120)
1 day cap adjustment 0.8% (1/120)

Summary of Postoperative Complications at the 3-Month Visita

Parameter Nil Trace Grade I
Microfolds 100.0% (120/120)
Epithelial ingrowth 99.2% (119/120) 0.8% (1/120)
Superficial punctuate keratitis 80.8% (97/120) 15.0% (18/120) 4.2% (5/120)
Interface haze/transient light sensitivity 85.0% (102/120) 13.3% (16/120) 1.7% (2/120)
Interface debris 96.7% (116/120) 3.3% (4/120)
Infection 100.0% (120/120)
Diffuse lamellar keratitis 100.0% (120/120)

Comparison of Outcomes for Low Myopic Corrections Between SMILE and LASIK

Author (y) Eyes Procedure/Femtosecond Laser SEQ (D) (Range) Cylinder (D) (Range) Time Point % CDVA 20/20 or Better % UDVA 20/20 or Better % SEQ Within ±0.50 D Loss 1 Line CDVA
Reinstein (2014) 110 SMILE / VisuMax −2.61 ± 0.55 (−1.03 to −3.50) −0.57 ± 0.39 (0.00 to −1.50) 1 year 100% 96% 84% 9%
de Benito-Llopis et al. (2007)25 79 LASIK / 217c −1.28 ± 0.40 (0.00 to −2.50) −0.50 ± 0.40 (0.00 to −1.50) 3 months 97% 88% 95% 29%
de Benito-Llopis et al. (2007)25 79 LASEK / 217c −1.30 ± 0.60 (0.00 to −2.50) −0.58 ± 0.40 (0.00 to −1.50) 3 months 96% 93% 91% 23%
FDA (2007)28 86a LASIK / S4 (0.00 to −4.00) (0.00 to −2.00) 6 months NR 87% 90% NR
FDA (2006)26 225a LASIK / MEL80 (0.00 to −4.00) (0.00 to −3.00) 3 months NR 95% 88% 8%
FDA (2003)27 391a LASIK / Allegretto (0.00 to −4.00) (0.00 to −3.00) 3 months NR 91% 93% NR
FDA (2003)29 209a LASIK / 217a (0.00 to −4.00) (0.00 to −3.00) 6 months NR 95% 81% NR
FDA (2003)31 228a LASIK / S4 (0.00 to −4.00) (0.00 to −3.00) 3 months NR 93% 92% NR
FDA (2002)30 95a LASIK / LADARVision (0.00 to −4.00) (0.00 to −0.50) 3 months NR 81% 81% NR

10.3928/1081597X-20141113-07

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