Journal of Refractive Surgery

Original Article Supplemental Data

Effect of Lowering Laser Energy on the Surface Roughness of Human Corneal Lenticules in SMILE

Yong Woo Ji, MD; Minseo Kim; David Sung Yong Kang, MD; Dan Z. Reinstein, MD, MA(Cantab), FRCSC; Timothy J. Archer, PhD; Jin Young Choi, MD; Eung Kweon Kim, MD, PhD; Hyung Keun Lee, MD, PhD; Kyoung Yul Seo, MD, PhD; Tae-im Kim, MD, PhD

Abstract

PURPOSE:

To determine the effect of lowering femtosecond laser energy on the surface quality of the intrastromal interface during small incision lenticule extraction (SMILE).

METHODS:

Forty age- and diopter-matched female patients (40 eyes) with moderate myopia received SMILE with different energy levels (100 to 150 nJ) and fixed spot separation (4.5 μm). Five human corneal lenticules from each energy group were evaluated by atomic force microscopy and scanning electron microscopy (SEM). Both anterior and posterior surface characteristics of the lenticules were assessed.

RESULTS:

All measurements of surface roughness were approximately three times higher and in the anterior and posterior surface of the lenticules with the energy level of 150 nJ than with 100 nJ (P < .001). Furthermore, atomic force microscopy analysis found that energy differences of 15 nJ or more made a significant difference in surface roughness at energy levels of 115 nJ or higher. Interestingly, there was no significant difference in all roughness values of both surfaces among the 100, 105, and 110 nJ groups. In addition, all values of surface roughness were significantly positively correlated with laser energy for both anterior and posterior surfaces of the lenticule (P < .001). Consistent with atomic force microscopy results, SEM also showed that the SMILE lenticules in the higher laser energy group had more irregular surfaces.

CONCLUSIONS:

Lowering laser energy levels can improve surface quality of the lenticule of SMILE. To achieve better visual outcomes with faster recovery after the procedure, it is recommended to reduce the laser energy to less than 115 nJ at a spot separation of 4.5 μm.

[J Refract Surg. 2017;33(9):617–624.]

Abstract

PURPOSE:

To determine the effect of lowering femtosecond laser energy on the surface quality of the intrastromal interface during small incision lenticule extraction (SMILE).

METHODS:

Forty age- and diopter-matched female patients (40 eyes) with moderate myopia received SMILE with different energy levels (100 to 150 nJ) and fixed spot separation (4.5 μm). Five human corneal lenticules from each energy group were evaluated by atomic force microscopy and scanning electron microscopy (SEM). Both anterior and posterior surface characteristics of the lenticules were assessed.

RESULTS:

All measurements of surface roughness were approximately three times higher and in the anterior and posterior surface of the lenticules with the energy level of 150 nJ than with 100 nJ (P < .001). Furthermore, atomic force microscopy analysis found that energy differences of 15 nJ or more made a significant difference in surface roughness at energy levels of 115 nJ or higher. Interestingly, there was no significant difference in all roughness values of both surfaces among the 100, 105, and 110 nJ groups. In addition, all values of surface roughness were significantly positively correlated with laser energy for both anterior and posterior surfaces of the lenticule (P < .001). Consistent with atomic force microscopy results, SEM also showed that the SMILE lenticules in the higher laser energy group had more irregular surfaces.

CONCLUSIONS:

Lowering laser energy levels can improve surface quality of the lenticule of SMILE. To achieve better visual outcomes with faster recovery after the procedure, it is recommended to reduce the laser energy to less than 115 nJ at a spot separation of 4.5 μm.

[J Refract Surg. 2017;33(9):617–624.]

Small incision lenticule extraction (SMILE) is the latest refractive surgical technique using only a femtosecond laser, which removes the corneal stromal lenticule through a small corneal incision ranging from 2 to 5 mm.1,2 This procedure could be achieved by using a femtosecond laser platform with higher firing frequency. Recently, the 500-kHz VisuMax (Carl Zeiss Meditec AG, Jena, Germany) platform with a pulse energy of 115 to 170 nJ has been used.1,3,4 Several studies have reported comparable or superior efficacy, predictability, and safety to other refractive surgery techniques, including femtosecond lenticule extraction (FLEx).4–7

However, SMILE still has an unresolved issue of slow recovery of visual acuity in the early postoperative period.8–10 It is well known that a smooth and regular optical interface surface is essential for visual acuity after any kind of corneal refractive surgery.11–13 Furthermore, some studies have reported that the surface regularity of the human corneal lenticule and posterior stroma depends on the energy settings.14–16 A recent retrospective study reported that a low energy level (100 nJ) during SMILE led to better clinical outcomes than a high energy level (180 nJ), but they could not scientifically explain the reason for their results.17

The purpose of the current study was to investigate the effect of the laser energy on the optical stromal interface during SMILE. Therefore, we morphologically and quantitatively evaluated the surface quality of the human lenticule by using scanning electron microscopy and atomic force microscopy after SMILE with various laser energy levels (100 to 150 nJ) at a fixed spot separation 4.5 μm.

Patients and Methods

Patients and Human Lenticule Samples

This experimental microscopic study was conducted as part of a prospective, randomized, comparative clinical study, which was approved by the Yonsei University College of Medicine Institutional Review Board, Seoul, South Korea (IRB No. 4-2016-0840). The study adhered to the tenets of the Declaration of Helsinki and followed good clinical practices. All patients provided informed consent after a detailed explanation of the possible risks and benefits of the study.

Patients were recruited from November 2016 to January 2017. All patients underwent a baseline preoperative assessment including anterior and posterior segment examinations. Inclusion criteria were: corneal thickness greater than 500 μm, manifest refractive sphere of −3.00 to −6.00 diopters (D), manifest refractive cylinder of less than 6.00 D, stable refractive error with a less than 0.50 D change in sphere and cylinder in the previous year, corrected distance visual acuity (CDVA) of 20/20 or better in both eyes, and age 20 years or older. Exclusion criteria were: severe ocular surface disease, any corneal disease, cataract, glaucoma, macular disease, or previous history of intraocular or corneal surgery. Patients with suspicion of keratoconus on corneal topography were also excluded.

After the patients were randomly allocated a laser energy level by means of permuted block randomization with the computed software, the right eye of each patient was included in the study unless contraindicated, in which case the left eye was used. In particular, in an attempt to eliminate patient characteristics as a confounding factor, corneal lenticules of only female patients who were age-matched (22 to 27 years old) and diopter-matched (spherical equivalent: −4.00 to −5.00 D) were included in the current experimental study.

Surgical Technique

The SMILE procedures were conducted in the Eyereum Eye Clinic (Seoul, South Korea). The target postoperative refraction was emmetropia in all eyes. Using standardized techniques (Video 1, available in the online version of this article), the surgery was performed by an experienced surgeon (DSYK) using the VisuMax laser platform (Carl Zeiss Meditec, Jena, Germany). The surgical parameters used during SMILE were as follows: repetition rate of 500 kHz, pulse energy of 100 to 150 nJ, spot separation of 4.5 μm (regardless of energy), cap thickness of 120 μm, and side-cut width of 2 mm in the 12-o'clock position with an angle of 90°. After the anterior (upper) and posterior (lower) planes of the lenticule had been well defined, the anterior and posterior interfaces were dissected with a microspatula with a blunt circular tip and extracted with microforceps. All surgical dissections were performed with one hand holding a Colibri forceps and grasping the conjunctiva and Tenon's tissues adjacent to the limbus in counter traction to steady the globe during the lenticule dissection. All manipulations and dissections were kept minimal with single sweeping movements from limbus to limbus. The spatula was slightly lifted superiorly during the dissection maneuver to facilitate tissue bridge removal. The integrity of the lenticule was also checked subsequently.

All surgical procedures were performed by one experienced surgeon (DSYK) in a controlled and monitored environment with the temperature between 21°C and 23°C and humidity between 45% and 55% on a 24-hour basis.

Postoperatively, 0.5% topical levofloxacin (Cravit; Santen Pharmaceutical Co., Ltd., Osaka, Japan) and 0.1% fluorometholone (FML; Allergan, Irvine, CA) were applied four times a day for 1 month. The dosage was gradually reduced over 3 months.

Measurement of Surface Roughness of the Human Lenticules by Atomic Force Microscopy

For atomic force microscopy, lenticules from each energy group were collected randomly on different days. They were hydrated with a balanced salt solution immediately after surgery. Each lenticule was attached to a microscope slide using double-sided sticky tape. The atomic force microscopy equipment used in this study was a NanoWizard I (JPK Instruments AG, Berlin, Germany), operated in the intermittent contact mode with an aluminum coating on the detector side of the Si3N4 cantilever tip and a 42 N/m force constant. Height images were recorded in three dimensions on each lenticule, and the average roughness (Ra), root mean square roughness (Rq), and 10-point mean height roughness (Rz) were obtained from these images. The examinations were performed on both the anterior (upper, cap-side) and posterior (lower, bed-side) surface of each lenticule. Atomic force microscopy analyses were conducted as quickly as possible to minimize dehydration of the lenticules, which was assumed to be minor because no significant differences were observed between the first and last measurements for each sample. A single area on the lenticule was imaged three times and measurements were averaged to ensure that the force exerted was not sufficient to damage the sample surface and cause artifacts. The central area of each specimen was imaged to examine the optical center and avoid the misinterpretation of artifacts due to forceps manipulation as surface features.

The equations for measuring the roughness are as follows:

  1. Average roughness (Ra):

    Ra (N,M)=1N∑x=1n (z(x,y)−z¯(x,y))
    Arithmetic average height (z):
    z¯ (N,M)=1N∑x=1n z(x,y)

  2. RMS roughness (Rq):

    Rq (N,M)=1N∑x=1n(z (x,y)−z¯(x,y))2

  3. 10-point mean height roughness (Rz):

    Rz (N,M)=1N∑i=15Rpi+1N∑i=15Rvi

Specimens were evaluated by one examiner (YWJ) in a marked fashion with regard to laser energy levels during the entire study period.

Scanning Electron Microscopic Examination

Each lenticule was fixed with 2% glutaraldehyde/paraformaldehyde in 0.1 M phosphate buffered saline (PBS), pH 7.4, for 2 hours and washed three times for 30 minutes in 0.1 M PBS. Lenticules were post-fixed for 2 hours with 1% OsO4 dissolved in 0.1 M PBS, dehydrated in a gradually ascending series of ethanol solutions (50% to 100%), infiltrated with isoamyl acetate, and dried in a critical point dryer (HCP-2; Hitachi, Tokyo, Japan). The samples were coated with gold by ion sputter (IB-3; Eiko Ltd., Tokyo, Japan) at 6 mA for 6 minutes, and then examined with a scanning electron microscope (FE SEM S-800; Hitachi, Tokyo, Japan) at an acceleration voltage of 10 to 20 kV and photographed at different magnifications ranging from 100 to 10,000×. Images were digitalized and stored as TIFF files in the microscope computer. Scanning electron microscopy examinations were performed on the anterior and posterior surfaces of the lenticules (anterior surface of the lenticule and posterior surface of the lenticule) in each group.

Statistical Analysis

All statistical analyses were performed using SPSS software (version 21; SPSS, Inc., Chicago, IL). A one-way analysis of variance test with Bonferroni correction was used to compare parameters among three or more groups in this study. Pearson's correlation test was used to analyze the correlation between surface roughness of the lenticule and energy level, and its correlation coefficient (r) was −1 ≤ r ≤1. In all statistical tests, a P value of less than .05 was considered statistically significant.

Results

Forty female patients (40 eyes) with moderate myopia were enrolled for this experimental study. After confirmation of uneventful surgeries, five human corneal lenticules were assessed in each energy level with a fixed spot separation of 4.5 μm: 100, 105, 110, 115, 120, 130, 140, and 150 nJ. Table 1 shows the preoperative demographics of the patients. There was no significant difference among the groups in terms of age, spherical equivalent refraction, corneal curvature, central corneal thickness, or intraoperative parameters (P > .05).

Preoperative Demographics of Patients in Small Incision Lenticule Extraction With Various Energy Levelsa

Table 1:

Preoperative Demographics of Patients in Small Incision Lenticule Extraction With Various Energy Levels

Determination of Surface Roughness of the Human Smile Lenticule

Because it was impossible to directly observe the optical interface surface of the patients receiving SMILE, we investigated the surface roughness of human lenticules using two different methods (atomic force microscopy and scanning electron microscopy). As shown in the representative atomic force microscopy images, the bright spots indicating a higher area of the surface had larger roughness values in SMILE using 140 and 150 nJ energy than using 100 and 110 nJ on each anterior and posterior surface of the lenticule. Moreover, their areas were greater on the posterior surface of the lenticule than on the anterior surface of the lenticule at each energy level (Figure 1). The Ra was approximately 2.6 times higher in the anterior and posterior surfaces of the lenticule with 150 nJ than with 100 nJ energy (P < .001) (Table 2, Figures AB, available in the online version of this article). When comparing Rq and Rz, the surface roughness was also almost three times higher in both surfaces with 150 nJ than with 100 nJ (P < .001 for Rq of anterior and posterior surface of the lenticule; P = .002 for Rz of anterior surface of the lenticule and P < .001 for Rz of posterior surface of the lenticule). The anterior surface of the lenticule with a laser energy of 140 and 150 nJ was rougher compared with those with 130 nJ or lower (P < .05, Figure A). Interestingly, there was no significant difference in the Ra, Rq, and Rz of both surfaces among the 100, 105, and 110 nJ energies, which had relatively lower roughness (Figures AB).

Representative topographic images from atomic force microscopy of the anterior and posterior surfaces of the human lenticules obtained from small incision lenticule extraction using various femtosecond laser energies with fixed spot separation 4.5 μm. The image area is 50 × 50 μm at the center of the lenticule. The vertical range of the displayed data is shown on the right side of each image. The zero point of the bar corresponds to the lowest valley point, whereas the upper limit of the bar is the highest peak point.

Figure 1.

Representative topographic images from atomic force microscopy of the anterior and posterior surfaces of the human lenticules obtained from small incision lenticule extraction using various femtosecond laser energies with fixed spot separation 4.5 μm. The image area is 50 × 50 μm at the center of the lenticule. The vertical range of the displayed data is shown on the right side of each image. The zero point of the bar corresponds to the lowest valley point, whereas the upper limit of the bar is the highest peak point.

Surface Roughness of Human Corneal Lenticules From Small Incision Lenticule Extraction Measured by Atomic Force Microscopy

Table 2:

Surface Roughness of Human Corneal Lenticules From Small Incision Lenticule Extraction Measured by Atomic Force Microscopy

Comparison of anterior surface roughness among human corneal lenticules obtained from small incision lenticule extraction using various femtosecond laser energies. ANOVA = analysis of variance

Figure A.

Comparison of anterior surface roughness among human corneal lenticules obtained from small incision lenticule extraction using various femtosecond laser energies. ANOVA = analysis of variance

Comparison of posterior surface roughness among human corneal lenticules obtained from small incision lenticule extraction using various femtosecond laser energies. ANOVA = analysis of variance

Figure B.

Comparison of posterior surface roughness among human corneal lenticules obtained from small incision lenticule extraction using various femtosecond laser energies. ANOVA = analysis of variance

The scanning electron microscopy findings supported the atomic force microscopy results. The SMILE lenticules with 140 and 150 nJ energy showed a more irregular anterior surface, and a more discernibly elevated and scale-like posterior surface, compared to the lenticules with 100 and 110 nJ. The posterior surface of the lenticule was more reticular than the anterior surface of the lenticule at each energy level (Figure 2A). Cavitation bubbles were observed at the anterior and posterior surfaces of the lenticule with an energy level of 115 nJ or higher (Figure 2B). However, no cavitation bubbles were detected by scanning electron microscopy on the lenticules created using energy of 100, 105, and 110 nJ.

Representative images of both surfaces of human lenticules by scanning electron microscopy. (A) The lenticule obtained from small incision lenticule extraction (SMILE) using conventional femtosecond laser energy (140 and 150 nJ) with a spot separation of 4.5 μm had a more irregular surface than that from SMILE using low energy (100 and 110 nJ) with the same spot separation on both the anterior and posterior surfaces. The posterior surface of the SMILE lenticule was rougher than the anterior surface at each energy level (× 300). (B) The cavitation bubbles were observed at the periphery of both surfaces of the lenticules from SMILE using laser energy of more than 120 nJ (× 300).

Figure 2.

Representative images of both surfaces of human lenticules by scanning electron microscopy. (A) The lenticule obtained from small incision lenticule extraction (SMILE) using conventional femtosecond laser energy (140 and 150 nJ) with a spot separation of 4.5 μm had a more irregular surface than that from SMILE using low energy (100 and 110 nJ) with the same spot separation on both the anterior and posterior surfaces. The posterior surface of the SMILE lenticule was rougher than the anterior surface at each energy level (× 300). (B) The cavitation bubbles were observed at the periphery of both surfaces of the lenticules from SMILE using laser energy of more than 120 nJ (× 300).

Correlation Between Surface Roughness and Femtosecond Laser Energy in Smile

Microscopic analysis of SMILE lenticules led us to investigate the correlation between surface roughness and SMILE energy level. Interestingly, all values of surface roughness were significantly positively correlated with laser energy for both anterior and posterior surfaces of the lenticule (Pearson coefficient r = 0.868, P < .001 for Ra of anterior surface of the lenticule; r = 0.843, P < .001 for Rq of anterior surface of the lenticule; r = 0.807, P < .001 for Rz of anterior surface of the lenticule; r = 0.920, P < .001 for Ra of posterior surface of the lenticule; r = 0.957, P < .001 for Rq of posterior surface of the lenticule; r = 0.857, P < .001 for Rz of posterior surface of the lenticule; Figure 3).

Correlation between surface roughness of the human lenticule and femtosecond laser energy in small incision lenticule extraction. The surface roughness of the lenticule was analyzed with respect to femtosecond laser energy level at a fixed spot separation of 4.5 μm. (A) Anterior surface of the human lenticule. (B) Posterior surface of the human lenticule (r, Pearson's correlation coefficient −1 ≤ r ≤1; r and P value by Pearson's correlation analysis; individual points and error bars represent the estimated means and standard deviation of three independent measures (nm at 2,500 μm2). n = 5 lenticules/group; Ra = average roughness; Rq = root mean square roughness; Rz = 10-point mean height roughness.

Figure 3.

Correlation between surface roughness of the human lenticule and femtosecond laser energy in small incision lenticule extraction. The surface roughness of the lenticule was analyzed with respect to femtosecond laser energy level at a fixed spot separation of 4.5 μm. (A) Anterior surface of the human lenticule. (B) Posterior surface of the human lenticule (r, Pearson's correlation coefficient −1 ≤ r ≤1; r and P value by Pearson's correlation analysis; individual points and error bars represent the estimated means and standard deviation of three independent measures (nm at 2,500 μm2). n = 5 lenticules/group; Ra = average roughness; Rq = root mean square roughness; Rz = 10-point mean height roughness.

Discussion

This study demonstrates that the anterior and posterior surfaces of the refractive lenticule, which correspond to the intrastromal interface surface, can become regular with no occurrence of cavitation bubbles using lower energy in SMILE. Interestingly, there was no significant difference in all roughness values of both surfaces among the 100, 105, and 110 nJ groups despite a highly positive correlation between surface roughness of the lenticule and energy level. Therefore, reducing the energy levels to less than 115 nJ may help improve visual outcomes during the early postoperative period in SMILE using a 500-kHz laser platform with a spot separation of 4.5 μm.

The remaining challenge in SMILE surgeries is the slow recovery of visual performance within the first week, especially at postoperative day 1.8–10 To resolve this problem, some surgeons have adjusted various femtosecond laser parameters during SMILE. Hjortdal et al. improved visual acuity at 1 day after SMILE by making laser spot distance wider with higher energy (4.5 μm with 170 nJ vs 2.5 μm with 125 nJ by 500-kHz VisuMax laser).13 On the other hand, it was reported that there was no difference in postoperative 1-week visual acuity between 140 nJ (spot distance: 3 μm) and 170 nJ (spot distance: 4.5 μm) energy generated by the 500-kHz VisuMax laser.10 However, most recently, a large retrospective study showed a better visual acuity and efficacy index in the 100 nJ energy group (164 eyes) than in the 180 nJ energy group (322 eyes) under spot distance controlled from day 1 to 3 months postoperatively.17

To identify how laser energy level affects SMILE outcomes independently, we focused on the roughness of lenticule surfaces considered as the intrastromal optical interface. Vinciguerra et al. provided a correlation between smooth optical surfaces and postoperative visual acuity after laser refractive surgeries.11,18 In SMILE, because two lamellar cuts are made by femtosecond laser, the two surfaces (cap-side and bed-side) become opposed to each other; some interface irregularity is inevitable and consequently affects visual outcomes. Our results revealed the anterior and posterior surfaces of the lenticule were significantly smoother when using lower energies. Moreover, the energy level had a highly positive correlation with the surface roughness of the anterior surface of the lenticule and posterior surface of the lenticule obtained from the SMILE procedure. Likewise, atomic force microscopy analyses of donor corneas undergoing preparation for endothelial keratoplasty showed that when lower energy lasers were used to dissect the donor tissue, the surface of the posterior stroma was more regular compared to when higher energy lasers were used.16 Also, it has been demonstrated that the surface regularity index decreased as laser energy increased during FLEx.14

Previous studies to evaluate the surface characteristics of FLEx or SMILE lenticules used only subjective criteria.12,14,15,19 Among them, some authors noted the smooth lenticule surfaces and the absence of surface irregularities by using environmental scanning electron microscopy for subjectively evaluating the anterior and posterior surfaces of SMILE lenticules.15 They used environmental scanning electron microscopy to eliminate artifacts due to tissue preparation; however, environmental scanning electron microscopy images are likely to look flat and smooth. Therefore, we used scanning electron microscopy for morphologic evaluation and objectively analyzed the surface roughness using atomic force microscopy. In contrast to the above study, our microscopic findings showed that the posterior surface of the lenticule was much rougher than the anterior surface of the lenticule. These are consistent with the scanning electron microscopy findings of other studies.12,19

In this study, the atomic force microscopy analysis found that differences of 15 nJ or more made a significant difference in surface roughness at energy levels of 115 nJ or higher with a fixed spot separation of 4.5 μm. Some studies have suggested that the smoothness of the lenticule might depend on careful surgical manipulation.12,19 For that reason, all surgical procedures were performed by one experienced surgeon in the current study. There was no difference in subjective ease of manual dissection of the lenticule in all of our SMILE cases even though we did not estimate it. Furthermore, scanning electron microscopy findings indicated that cavitation bubbles considered as opaque bubble layer occurred at both surfaces of the lenticule during SMILE with 115 nJ or more.20 Therefore, our experimental microscopic results presented a fiducial level of 115 nJ when lowering laser energy during SMILE with spot separation 4.5 μm. Further clinical studies on the intraoperative situation are needed to support our experimental studies.

There are some limitations of this study. First, we focused only on the surface roughness of the lenticule, although laser energy levels may affect several mechanisms, such as postoperative inflammation and intraocular scattering.21,22 Second, we measured only the central part of 2,500 μm2 for five samples per group, although atomic force microscopy is a powerful technique for analysis of delicate surfaces. Furthermore, the current experimental microscopic study may not reflect the actual human optic condition. Because human visual performance is a complex and sophisticated process, large clinical studies must be conducted.

Modulation of laser energy at a fixed spot separation can make both surfaces of the lenticule smooth. In particular, to achieve better visual outcomes with faster recovery after SMILE, it may be necessary to reduce femtosecond laser energy to less than 115 nJ at a spot separation of 4.5 μm. The optimization of various femtosecond laser parameters within a well-organized randomized clinical study should be investigated in the future.

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Preoperative Demographics of Patients in Small Incision Lenticule Extraction With Various Energy Levelsa

Characteristic100 nJ105 nJ110 nJ115 nJ120 nJ130 nJ140 nJ150 nJPb
Age (y)23.2 ± 2.624.6 ± 3.024.8 ± 2.123.8 ± 2.224.8 ± 2.324.0 ± 2.125.4 ± 2.924.0 ± 2.6.617
SE (D)−4.87 ± 0.47−4.86 ± 0.43−4.57 ± 0.38−4.81 ± 0.56−4.79 ± 0.33−4.46 ± 0.68−4.91 ± 0.51−4.81 ± 0.55.897
Average K (D)43.32 ± 0.4643.08 ± 0.8443.12 ± 0.3143.09 ± 0.8143.06 ± 0.9643.08 ± 0.4843.03 ± 0.7743.09 ± 0.63.930
CCT (μm)548.2 ± 18.6548.4 ± 26.4550.6 ± 9.1546.4 ± 15.0555.0 ± 17.8557.2 ± 24.2555.0 ± 17.4556.0 ± 29.5.296
Optical zone diameter (mm)6.74 ± 0.306.78 ± 0.136.76 ± 0.296.94 ± 186.92 ± 0.116.86 ± 0.226.80 ± 0.216.66 ± 0.11.260
Cap diameter (mm)7.82 ± 0.227.76 ± 0.137.98 ± 0.028.11 ± 0.517.91 ± 0.107.85 ± 0.217.79 ± 0.207.66 ± 0.11.091
Cap thickness (μm)120120120120120120120120
Lenticule thickness (μm)114.2 ± 6.3112.0 ± 2.9115.8 ± 9.1113.6 ± 5.8121.8 ± 9.0115.2 ± 10.0118.8 ± 9.2113.0 ± 10.8.842

Surface Roughness of Human Corneal Lenticules From Small Incision Lenticule Extraction Measured by Atomic Force Microscopy

Parameter100 nJ105 nJ110 nJ115 nJ120 nJ130 nJ140 nJ150 nJ
Anterior surface
  Ra282.13 ± 58.71311.53 ± 93.95388.47 ± 57.05415.04 ± 71.89416.63 ± 85.67433.23 ± 76.72699.73 ± 86.17741.03 ± 140.47
  Rq363.90 ± 85.89402.70 ± 106.08474.77 ± 36.08486.11 ± 36.50477.63 ± 70.38523.70 ± 78.641,009.17 ± 213.781,127.17 ± 285.93
  Rz3,347.62 ± 1,487.293,430.10 ± 592.553,661.33 ± 258.214,027.58 ± 715.223,893.87 ± 484.413,914.00 ± 323.277,891.05 ± 2,030.018,561.55 ± 1,746.80
Posterior surface
  Ra546.53 ± 67.44582.70 ± 62.77778.40 ± 90.50968.70 ± 241.101,002.30 ± 116.821,222.00 ± 141.171,303.65 ± 74.611,408.13 ± 111.43
  Rq659.37 ± 157.45727.60 ± 50.66921.30 ± 87.761,165.33 ± 198.601,198.20 ± 140.731,400.07 ± 119.721,684.17 ± 130.241,862.61 ± 124.60
  Rz4,705.34 ± 2,437.525,583.43 ± 1,751.637,531.10 ± 1,270.379,396.04 ± 1,976.419,636.13 ± 901.638,873.39 ± 826.3810,736.27 ± 437.9813,882.11 ± 273.45
Authors

From the Institute of Vision Research (YWJ, EKK, HKL, KYS, TK) and Corneal Dystrophy Research Institute (YWJ, EKK, HKL, KYS, TK), Department of Ophthalmology, Yonsei University College of Medicine, Seoul, South Korea; Hankuk Academy of Foreign Studies, Yongin, South Korea (MK); Eyereum Eye Clinic, Seoul, South Korea (DSYK, JYC); London Vision Clinic, London, United Kingdom (DZR, TJA); the Department of Ophthalmology, Columbia University Medical Center, New York (DZR); Centre Hospitalier National d'Ophtalmologie, Paris, France (DZR); and Biomedical Science Research Institute, University of Ulster, Coleraine, Northern Ireland (DZR, TJA).

Dr. Reinstein is a consultant for Carl Zeiss Meditec (Carl Zeiss Meditec AG, Jena, Germany) and has a proprietary interest in the Artemis technology (ArcScan, Inc., Golden, Colorado) through patents administered by the Center for Technology Licensing at Cornell University (CTL), Ithaca, New York. The remaining authors have no proprietary or financial interest in the materials presented herein.

Supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (NRF-2016R1A2B4009626).

AUTHOR CONTRIBUTIONS

Study concept and design (YWJ, DSYK, KYS, TK); data collection (YWJ, DSYK, JYC, HKL); analysis and interpretation of data (YWJ, MK, DZR, TJA, EKK, TK); writing the manuscript (YWJ, DZR, TJA, TK); critical revision of the manuscript (YWJ, MK, DSYK, JYC, EKK, HKL, KYS, TK); administrative, technical, or material support (MK, TK); supervision (DSYK, HKL, TK)

Correspondence: Tae-im Kim, MD, PhD, Department of Ophthalmology, Yonsei University College of Medicine, 50-1 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea. E-mail: tikim@yuhs.ac

Received: March 11, 2017
Accepted: May 26, 2017

10.3928/1081597X-20170620-02

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