Journal of Refractive Surgery

Original Article Supplemental Data

Wavefront-Guided LASIK Has Comparable Ocular and Corneal Aberrometric Outcomes but Better Visual Acuity Outcomes Than SMILE in Myopic Eyes

Rohit Shetty, MD, PhD, FRCS; Himnashu Matalia, MD; Chinnappaiah Nandini, MD; Ashwatha Shetty, MD; Pooja Khamar, MD; Tushar Grover, MD; Abhijit Sinha Roy, PhD

Abstract

PURPOSE:

To compare ocular and corneal aberrometric outcomes of wavefront-guided (WFG) LASIK and small incision lenticule extraction (SMILE).

METHODS:

This was a prospective, interventional study where 48 eyes (24 patients) underwent SMILE (Carl Zeiss Meditec, Jena, Germany) and 58 eyes (29 patients) underwent WFG LASIK (Abbott Medical Optics, Abbott Park, IL). Visual acuity and ocular surface disease index were assessed preoperatively and 1 and 3 months postoperatively. Corneal topography and anterior aberrations were assessed with the Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany) and iTrace (Tracey Technologies, Houston, TX), respectively. Ocular aberrations were also assessed with the iTrace.

RESULTS:

Safety and efficacy indexes of WFG LASIK (0.99 and 1.01, respectively) and SMILE (1.01 and 1.13, respectively) were comparable, although WFG LASIK was better (P < .0001). At 3 months postoperatively, all eyes in both groups achieved an uncorrected distance visual acuity of 20/20 or better. Further, 74.14% and 45.83% of the eyes in the WFG LASIK and SMILE groups, respectively, achieved uncorrected distance visual acuity of 20/16 (P = .003). The Pentacam reported an increase in root mean square of higher order aberrations (diameter of 4 mm and 6th order Zernike) and coma with a decrease in spherical aberration in both groups (P < .001). Corneal aberrations from the iTrace also did not yield any definitive differences between the treatments. However, changes in ocular aberrations were clinically insignificant at 3 months after both treatments. The ocular surface disease index increased mildly after WFG LASIK (P > .05) but was unchanged after SMILE.

CONCLUSIONS:

WFG LASIK and SMILE had similar aberrometric outcomes but WFG LASIK had better postoperative visual acuity. Surgeon experience, internal aberrations, small pupil size, and wound healing can enable similar outcomes in both procedures.

[J Refract Surg. 2018;34(8):527–532.]

Abstract

PURPOSE:

To compare ocular and corneal aberrometric outcomes of wavefront-guided (WFG) LASIK and small incision lenticule extraction (SMILE).

METHODS:

This was a prospective, interventional study where 48 eyes (24 patients) underwent SMILE (Carl Zeiss Meditec, Jena, Germany) and 58 eyes (29 patients) underwent WFG LASIK (Abbott Medical Optics, Abbott Park, IL). Visual acuity and ocular surface disease index were assessed preoperatively and 1 and 3 months postoperatively. Corneal topography and anterior aberrations were assessed with the Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany) and iTrace (Tracey Technologies, Houston, TX), respectively. Ocular aberrations were also assessed with the iTrace.

RESULTS:

Safety and efficacy indexes of WFG LASIK (0.99 and 1.01, respectively) and SMILE (1.01 and 1.13, respectively) were comparable, although WFG LASIK was better (P < .0001). At 3 months postoperatively, all eyes in both groups achieved an uncorrected distance visual acuity of 20/20 or better. Further, 74.14% and 45.83% of the eyes in the WFG LASIK and SMILE groups, respectively, achieved uncorrected distance visual acuity of 20/16 (P = .003). The Pentacam reported an increase in root mean square of higher order aberrations (diameter of 4 mm and 6th order Zernike) and coma with a decrease in spherical aberration in both groups (P < .001). Corneal aberrations from the iTrace also did not yield any definitive differences between the treatments. However, changes in ocular aberrations were clinically insignificant at 3 months after both treatments. The ocular surface disease index increased mildly after WFG LASIK (P > .05) but was unchanged after SMILE.

CONCLUSIONS:

WFG LASIK and SMILE had similar aberrometric outcomes but WFG LASIK had better postoperative visual acuity. Surgeon experience, internal aberrations, small pupil size, and wound healing can enable similar outcomes in both procedures.

[J Refract Surg. 2018;34(8):527–532.]

Small incision lenticule extraction (SMILE) and wavefront-guided (WFG) LASIK are among the latest refractive procedures.1–10 SMILE and WFG LASIK use different algorithms to achieve the same refractive change in a patient. Thus, WFG LASIK and SMILE may yield different aberrometric outcomes depending on the nature of wound healing and biomechanical response of the tissue.2 Visual acuity and refractive outcomes were mostly similar between SMILE and WFG LASIK eyes, although WFG LASIK may yield more eyes with UDVA better than 20/20.1–10 Further, only one study profiled the change in corneal aberrations between WFG LASIK and SMILE7 and none have evaluated both corneal and ocular aberrations in the same study groups.

Therefore, the aim of this study was to assess the change in ocular and corneal aberrations after WFG LASIK and SMILE in eyes having low to high myopia and similar scan diameters for aberrometry. Additionally, visual acuity and tomographic changes were compared between WFG LASIK and SMILE eyes (preoperatively and 1- and 3-month postoperatively).

Patients and Methods

This was a prospective, interventional, and longitudinal study approved by the ethics committee of Narayana Nethralaya Eye Hospital, Bangalore, India. A written informed consent was obtained from all patients. The study followed the tenets of the Declaration of Helsinki. Inclusion criteria were stable refraction (less than −12.00 diopters [D] equivalent refraction with astigmatism not more than −3.00 D) for a period of 1 year (change less than 0.25 D). Patients with central corneal thickness less than 480 μm or a history of keratoconus, diabetes mellitus, collagen vascular disease, pregnancy, breastfeeding, any known ocular pathology, and any prior ocular surgery or trauma were excluded from the study. In all eyes, calculated residual stromal thickness was greater than 250 μm. Contact lens use was discontinued for at least 2 weeks prior to any measurements.

All patients underwent assessment of uncorrected (UDVA) and corrected (CDVA) distance visual acuity. Corneal tomography was assessed with the Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany). Corneal front surface aberration from the Pentacam was analyzed with Zernike polynomials (6th order and diameter of 4 mm). Corneal and ocular aberrations were also assessed with the iTrace aberrometer (Tracey Technologies, Houston, TX). The iTrace was chosen as an unbiased device because the two lasers were located at different sites and the iTrace was common to both treatment sites. The ocular surface discomfort index score was also evaluated. All measurements and evaluations were performed preoperatively and 1 and 3 months postoperatively.

A total of 48 eyes (24 patients) underwent SMILE with the VisuMax femtosecond laser system (Carl Zeiss Meditec, Jena, Germany) (operated by RS). A total of 58 eyes (29 patients) underwent WFG LASIK with the STAR S4IR excimer laser and iDesign system for treatment calculation (Abbott Medical Optics, Abbott Park, IL) (operated by HM). In the WFG-LASIK procedure, flap diameter, optical diameter, and flap thickness were set to 9 mm, 6 mm, and 100 μm, respectively. After flap creation with the Intralase femtosecond laser (Abbott Medical Optics), the exposed stromal bed was ablated with the STAR S4IR excimer laser. In the SMILE procedure, the cap diameter, lenticule diameter, and cap thickness were set to 7.7 mm, 6 mm, and 110 μm, respectively. Laser cut energy index was preset at 170 nJ. Spot spacing was 2 μm for creation of the lenticule side cut and 4.5 μm for creation of the lenticule. Track distance was 3 mm. After the incision was made, the lenticule was cut with the laser and extracted manually. Intraoperative cap repositioning was performed in all SMILE eyes. After the surgery, one drop of moxifloxacin hydrochloride 0.5% (Vigamox; Alcon Laboratories, Inc., Fort Worth, TX) was applied to both eyes. A routine postoperative regimen was followed for both eyes. This included moxifloxacin hydrochloride 0.5% eye drops (Vigamox) four times a day for 1 week and tapering doses of topical 1% fluorometholone eye drops (Flarex; Alcon Laboratories, Inc.) up to 1 month and topical lubricants (Optive; Allergan, Inc., Irvine, CA) up to 3 months. The above regimen was the same for all WFG LASIK and SMILE eyes.

Statistical Analyses

All continuous variables were assessed for normality of distribution. Because many of the variables were not normally distributed, non-parametric statistical tests were used. To compare preoperative with postoperative data within a treatment group, the paired Wilcoxon test was used. The change in variables due to surgery was also calculated. These were analyzed with the independent samples Mann–Whitney test. Variables analyzed included keratometry, visual acuity, central corneal thickness, anterior surface corneal aberrations from the Pentacam and iTrace, and ocular aberrations from the iTrace. The medians with ranges of the variables were compiled. All statistical analyses were performed with MedCalc software (version 18; MedCalc, Inc., Ostend, Belgium). A P value of less than .05 was considered statistically significant.

Results

Preoperative demographics were similar between groups, except for CDVA (Table 1). However, this difference in preoperative CDVA was statistically significant but not clinically significant. At 3 months postoperatively, safety index (mean ± standard deviation) was 0.99 ± 0.04 and 0.90 ± 0.10 in the WFG LASIK and SMILE groups, respectively (P < .0001). Efficacy index was 1.01 ± 0.04 and 1.13 ± 0.14 in the WFG LASIK and SMILE groups, respectively (P < .0001). At 3 months postoperatively, 100% of eyes achieved UDVA of 20/20 or better in both groups. Further, 74.14% and 45.83% of the eyes in the WFG LASIK and SMILE groups achieved UDVA of 20/16 at 3 months postoperatively, respectively (P = .003). The postoperative outcomes after WFG LASIK related to keratometry, UDVA, CDVA, and central corneal thickness were significant due to surgical alterations (Table A, available in the online version of this article, P < .0001). At both postoperative time points, the Pentacam reported a significant decrease (all P < .001) in root mean square (RMS) of anterior corneal surface higher order aberrations (HOAs), anterior surface spherical aberration, and RMS of anterior surface coma (Table A). At both postoperative follow-up visits (Table A), the iTrace reported a significant decrease in RMS of anterior corneal surface (P < .001), RMS of ocular lower order aberrations (LOAs) (P < .0001), and anterior surface spherical aberration (P < .05). Postoperative ocular aberrations other than LOAs and spherical aberration (3 months postoperatively) were clinically similar to preoperative levels (Table A). Particularly, ocular spherical aberration decreased significantly at 3 months (P = .01). Scan area on the iTrace for measurement of aberrations was statistically similar between the time points and was automatically chosen by the iTrace (Table A).

Preoperative Demographicsa

Table 1:

Preoperative Demographics

Comparison of Preoperative and Postoperative Outcomes in the WFG LASIK Groupa

Table A:

Comparison of Preoperative and Postoperative Outcomes in the WFG LASIK Group

Table B (available in the online version of this article) shows the postoperative outcomes after SMILE. Both the Pentacam and iTrace reported a significant increase in RMS of anterior corneal surface HOAs and coma, whereas the Pentacam showed a decrease in anterior spherical aberration (Table B). Similar to WFG LASIK, ocular aberrations were clinically similar to preoperative levels except for RMS of LOAs (Table B). Scan area on the iTrace for measurement of aberrations was statistically similar between the time points (Table B). The ocular surface discomfort index remained similar between preoperative and postoperative time points for both WFG LASIK and SMILE eyes. Table 1 compared the postoperative tomographic and aberrometric outcomes at 3 months between groups. Keratometry magnitudes were similar between groups (P > .05). The Pentacam showed mostly similar front surface aberrations between groups (P > .05) except for spherical aberration (P = .002). However, these results were different when measured with the iTrace Placido topographer (Table 1). RMS of ocular LOAs and spherical aberration were statistically similar between the groups (P = .10), although the magnitude was higher in SMILE eyes. However, RMS of ocular HOA and coma were greater in the SMILE eyes at 3 months postoperatively (P < .05).

Comparison of Preoperative and Postoperative Outcomes in the SMILE Groupa

Table B:

Comparison of Preoperative and Postoperative Outcomes in the SMILE Group

Discussion

This study investigated primary changes in corneal and ocular aberrations after WFG LASIK and SMILE in eyes with myopic refractive error. Other outcomes such as visual acuity, safety index, and efficacy index were also evaluated. There were clear differences noted in terms of anterior corneal surface aberrometry between WFG LASIK and SMILE, which also depended on the measurement method (Scheimpflug vs Placido topography). Changes in ocular aberrations were clinically insignificant after both procedures, despite changes in anterior corneal surface aberrations. Overall, both WFG LASIK and SMILE had comparable safety and efficacy. However, more WFG LASIK eyes than SMILE eyes achieved UDVA of 20/16 after surgery (P = .003).

Tables AB provide a comprehensive summary of the study outcomes. A salient feature of this study was that all aberrations were measured for the in situ pupil size of individual eyes, which was similar at all time points. Decrease in keratometry was as expected. The Pentacam revealed anterior corneal surface aberrations (RMS of HOAs) increased after both treatments. Despite a decrease in anterior corneal surface spherical aberration in both treatments, an increase in RMS of coma aberration of the surface probably compensated for it, leading to an increase in RMS of HOAs. Interestingly, an increase in anterior surface RMS of coma and HOAs were detected only by the Pentacam. The iTrace outcomes were conflicted for the anterior corneal surface. Whereas RMS of coma increased in SMILE eyes, spherical aberration decreased in WFG LASIK eyes. Placido measurement is sensitive to state of the tear film, but has better measurement resolution than the Pentacam. Thus, discordance between the Pentacam and Placido postoperative corneal surface data (Tables AB) could be attributed to these effects. Also, this discordance was present in both WFG LASIK and SMILE eyes. On the other hand, ocular aberrometry from the iTrace showed that all aberrations were clinically maintained (or a small change was detected) to preoperative level except for RMS of LOAs in both groups and spherical aberration in WFG LASIK eyes. Thus, any change in HOAs of anterior corneal surface appeared to be compensated for by the internal optics (lens and media) in both WFG LASIK and SMILE eyes. Despite similar performance of WFG LASIK and SMILE in terms of ocular aberrometry, more eyes achieved UDVA better than 20/20 in the WFG LASIK group. There was a decrease in ocular spherical aberration in WFG LASIK eyes but not in SMILE eyes (Table B). In Table 2, SMILE eyes had a greater median ocular spherical aberration than WFG LASIK eyes. This could have led to the trends observed with postoperative UDVA between the study cohorts. Considering that dryness and postoperative wound healing was expected to be better in SMILE eyes than in WFG LASIK eyes,1 this outcome was interesting and would need further study.

Comparison of Postoperative (3-Month) Tomographic and Aberrometric Valuesa

Table 2:

Comparison of Postoperative (3-Month) Tomographic and Aberrometric Values

Few studies have compared the outcomes of WFG LASIK and SMILE. Khalifa et al.2 reported an increase in RMS of ocular HOAs, ocular trefoil, and RMS of ocular coma in both WFG LASIK and SMILE eyes, with the increase being lower in WFG LASIK eyes. Ocular spherical aberration remained unchanged in both groups.2 A pupil size of 5 mm was reported in the above study. Only 77.97% and 90.20% achieved postoperative UDVA of 20/20 or better in SMILE and WFG LASIK eyes, respectively. Safety and efficacy indices were similar to our results.2 Zhang et al.3 also performed a comparative study in patients with high astigmatism (> 2.25 D). Although both procedures were safe, undercorrection existed in both groups by the same amount,3 although the flap was hypothesized to induce astigmatism by itself.11

Kung et al.5 also reported that WFG outcomes were statistically better than the outcomes of wavefront-optimized method. Further, patients reported better day and night vision in the WFG group.5 Yu et al.6 reported similar outcomes between different WFG systems. Subjective preference of platforms was also statistically similar.6 Thus, WFG LASIK tends to be better than conventional LASIK platforms using aspheric ablation.

Ye et al.7 evaluated anterior corneal surface aberration within the central 6-mm zone in eyes with moderate to high myopia. RMS of HOAs, spherical aberration, and horizontal coma increased in the WFG LASIK and SMILE groups and only vertical coma increased in the SMILE group.7 They attributed the increase in vertical coma to lack of iris registration in SMILE and in situ cyclotorsion of the eye. This may have resulted in decentration of the lenticule.7 Chen et al.8 reported similar UDVA and CDVA after WFG LASIK and SMILE but an increase in ocular vertical coma and RMS of ocular HOAs after both procedures within a pupil size of 5 mm. The increase was the same between WFG LASIK and SMILE.8 Although the pupil diameter of most patients was smaller than 6 mm,7 the trends observed with corneal coma were similar to the trends observed with ocular coma, with SMILE eyes generally showing a greater increase.2–8 Another recent study also noted a tendency toward undercorrection of astigmatism in SMILE eyes.9 Studies also exist where SMILE provided a better ocular aberrometric outcome and postoperative patient experience in terms of dryness than LASIK.12,13 In our study, surgeon experience in delivering the treatment to the patient also could have played a significant role in achieving similar ocular aberrometric outcomes because both surgeons were highly experienced in WFG LASIK and SMILE.

A limitation of this study was that the natural pupil sizes of the patient were small, which prevented testing of the eye for aberrations over a larger area. Unfortunately, we cannot statistically control these sizes and our population tends to have smaller pupil sizes. Pupil sizes are not presented in many clinical studies on refractive surgery outcomes and could be an important determinant of visual acuity after surgery. This needs to be investigated further in future studies. Less dryness and discomfort after SMILE than after LASIK is well documented.1,4,12 The ocular surface discomfort index was similar between the treatment groups before surgery. In WFG LASIK, there was a slight increase in discomfort after surgery but the change was insignificant. In SMILE eyes, discomfort levels were virtually unchanged after surgery. Both WFG LASIK and SMILE were similar in terms of safety, efficacy, and visual outcomes. A recent study showed that SMILE eyes had no significant regression up to 2 years after surgery, whereas WFG LASIK eyes had regression ranging up to 0.50 D.10 This could be due to better wound healing response and fewer biomechanical changes (hypothesized) in SMILE eyes.14 The authors concluded that SMILE had better long-term refractive predictability.10,14

An optimum combination of energy and spot track distance led to better UDVA after SMILE.15 This could further reduce the differences in visual acuity (better than 20/20) between the procedures observed in this study. As the energy was reduced, postoperative UDVA became better,15 but at the expense of increased difficulty in separation of the lenticule from the surrounding stroma. Further studies with longer duration of follow-up and randomization are needed to confirm this trend. Specifically, a contralateral eye study design would be better to study regression of myopia.

References

  1. Kobashi H, Kamiya K, Shimizu K. Dry eye after small incision lenticule extraction and femtosecond laser-assisted LASIK: meta-analysis. Cornea. 2017;36:85–91. doi:10.1097/ICO.0000000000000999 [CrossRef]
  2. Khalifa MA, Ghoneim A, Shafik Shaheen M, Aly MG, Piñero DP. Comparative analysis of the clinical outcomes of SMILE and wavefront-guided LASIK in low and moderate myopia. J Refract Surg. 2017;33:298–304. doi:10.3928/1081597X-20170222-01 [CrossRef]
  3. Zhang J, Wang Y, Chen X. Comparison of moderate- to high-astigmatism corrections using wavefront-guided laser in situ keratomileusis and small-incision lenticule extraction. Cornea. 2016;35:523–530. doi:10.1097/ICO.0000000000000782 [CrossRef]
  4. Chen LY, Manche EE. Comparison of femtosecond and excimer laser platforms available for corneal refractive surgery. Curr Opin Ophthalmol. 2016;27:316–322. doi:10.1097/ICU.0000000000000268 [CrossRef]
  5. Kung JS, Manche EE. Quality of vision after wavefront-guided or wavefront-optimized LASIK: a prospective randomized contralateral eye study. J Refract Surg. 2016;32:230–236. doi:10.3928/1081597X-20151230-01 [CrossRef]
  6. Yu CQ, Manche EE. Subjective quality of vision after myopic LASIK: prospective 1-year comparison of two wavefront-guided excimer lasers. J Refract Surg. 2016;32:224–229. doi:10.3928/1081597X-20151222-03 [CrossRef]
  7. Ye MJ, Liu CY, Liao RF, Gu ZY, Zhao BY, Liao Y. SMILE and wavefront-guided LASIK out-compete other refractive surgeries in ameliorating the induction of high-order aberrations in anterior corneal surface. J Ophthalmol. 2016;2016:8702162. doi:10.1155/2016/8702162 [CrossRef]
  8. Chen X, Wang Y, Zhang J, Yang SN, Li X, Zhang L. Comparison of ocular higher-order aberrations after SMILE and wavefront-guided femtosecond LASIK for myopia. BMC Ophthalmol. 2017;17:42. doi:10.1186/s12886-017-0431-5 [CrossRef]
  9. Khalifa MA, Ghoneim AM, Shaheen MS, Piñero DP. Vector analysis of astigmatic changes after small-incision lenticule extraction and wavefront-guided laser in situ keratomileusis. J Cataract Refract Surg. 2017;43:819–824. doi:10.1016/j.jcrs.2017.03.033 [CrossRef]
  10. Kobashi H, Kamiya K, Igarashi A, Takahashi M, Shimizu K. Two-years results of small-incision lenticule extraction and wavefront-guided laser in situ keratomileusis for myopia. Acta Ophthalmol. 2018;96:e119–e126. doi:10.1111/aos.13470 [CrossRef]
  11. Christiansen SM, Mifflin MD, Edmonds JN, Simpson RG, Moshirfar M. Astigmatism induced by conventional spherical ablation after PRK and LASIK in myopia with astigmatism < 1.00 D. Clin Ophthalmol. 2012;6:2109–2117. doi:10.2147/OPTH.S37489 [CrossRef]
  12. Ganesh S, Gupta R. Comparison of visual and refractive outcomes following femtosecond laser-assisted LASIK with SMILE in patients with myopia or myopic astigmatism. J Refract Surg. 2014;30:590–596. doi:10.3928/1081597X-20140814-02 [CrossRef]
  13. Ganesh S, Brar S, Pawar A. Matched population comparison of visual outcomes and patient satisfaction between 3 modalities for the correction of low to moderate myopic astigmatism. Clin Ophthalmol. 2017;11:1253–1263. doi:10.2147/OPTH.S127101 [CrossRef]
  14. Zhang Y, Shen Q, Jia Y, Zhou D, Zhou J. Clinical outcomes of SMILE and FS-LASIK used to treat myopia: a meta-analysis. J Refract Surg. 2016;32:256–265. doi:10.3928/1081597X-20151111-06 [CrossRef]
  15. Li L, Schallhorn JM, Ma J, Cui T, Wang Y. Energy setting and visual outcomes in SMILE: a retrospective cohort study. J Refract Surg. 2018;34:11–16. doi:10.3928/1081597X-20171115-01 [CrossRef]

Preoperative Demographicsa

CharacteristicWFG LASIKSMILEP
Age (y)25 (20 to 34)23 (21 to 35).06
UDVA (logMAR)1.2 (0.6 to 1.5)1.3 (0.5 to 1.8).42
Sphere (D)−4.25 (−7.37 to −1.75)−4.50 (−10.00 to −2.25).28
Cylinder (D)−0.63 (−3.75 to 0.00)−0.75 (−3.75 to 0.75).99
Spherical equivalent (D)−4.75 (−8.25 to −1.75)−4.63 (−11.63 to −2.25).49
CVDA (logMAR)−0.1 (−0.1 to 0)0 (0 to 0.2)< .0001
Scan diameter on iTrace (mm)3.8 (2.9 to 4.0)3.9 (2.3 to 4.0).87
K1 (D)43.50 (39.30 to 47.20)43.80 (39.70 to 46.40).12
K2 (D)44.70 (40.50 to 47.80)44.70 (40.40 to 48.20).23
Kmean (D)44.15 (39.90 to 47.50)44.25 (40.20 to 47.30).21
Minimum corneal thickness (μm)523.5 (483 to 566)513.5 (475, 575).25
Ocular surface discomfort index6.25 (2.1 to 8.3)11.46 (7.0 to 28.7).18
Front LOA Pentacam (RMS, μm)0.48 (0.15 to 1.51)0.54 (−0.305 to 0.91).69
Front HOA Pentacam (RMS, μm)0.10 (0.03 to 0.18)0.10 (−0.08 to 0.16).62
Front SA Pentacam (μm)0.04 (−0.03 to 0.08)0.04 (−0.10 to 0.09).83
Front coma Pentacam (RMS, μm)−0.03 (−0.12 to 0.13)−0.03 (−0.09 to 0.07).41
Front LOA iTrace (RMS, μm)0.28 (0.07 to 1.35)0.35 (0.02 to 0.87).24
Front HOA iTrace (RMS, μm)0.08 (0.02 to 0.44)0.09 (0.02 to 0.22).93
Front SA iTrace (μm)0.04 (−0.003 to 0.10)0.04 (0.01 to 0.10).08
Front coma iTrace (RMS, μm)0.04 (0 to 0.21)0.04 (0.01 to 0.18).98
Ocular LOA iTrace (RMS, μm)2.64 (1.25 to 4.69)2.61 (0.09 to 4.97).68
Ocular HOA iTrace (RMS, μm)0.12 (0.05 to 0.3)0.14 (0.02 to 2.20).05
Ocular SA iTrace (μm)0.02 (−0.05 to 0.44)0.02 (−0.05 to 0.17).66
Ocular coma iTrace (RMS, μm)0.05 (0.01 to 0.17)0.06 (0.01 to 0.44).45

Comparison of Postoperative (3-Month) Tomographic and Aberrometric Valuesa

ParameterWFG LASIKSMILEPb
Scan diameter on iTrace (mm)3.50 (2.90 to 4.00)3.95 (2.10 to 5.00).09
K1 (D)40.30 (35.00 to 43.70)40.45 (32.40 to 44.20).87
K2 (D)40.95 (35.90 to 44.70)41.10 (33.50 to 44.70).87
Kmean (D)40.70 (35.50 to 44.10)40.75 (33.00 to 44.20).91
Minimum corneal thickness (μm)454.5 (411 to 514)446 (400 to 529).15
Front LOA Pentacam (RMS, μm)0.55 (0.16 to 0.99)0.52 (0.12 to 0.94).60
Front HOA Pentacam (RMS, μm)0.15 (0.06 to 0.26)0.16 (0.08 to 0.37).99
Front SA Pentacam (μm)0.03 (−0.019 to 0.11−0.001 (−0.076 to 0.10).002
Front coma Pentacam (RMS, μm)0.13 (0.034 to 0.250)0.130 (0.017 to 0.34).31
Front LOA iTrace (RMS, μm)0.23 (0.05 to 0.51)0.43 (0.05 to 0.84).0007
Front HOA iTrace (RMS, μm)0.09 (0.02 to 0.39)0.16 (0.04 to 0.61).0004
Front SA iTrace (μm)0.02 (−0.01 to 0.10)0.06 (−0.013 to 0.16).0008
Front coma iTrace (RMS, μm)0.07 (0 to 0.36)0.10 (0.02 to 0.55).009
Ocular LOA iTrace (RMS, μm)0.60 (0.05 to 1.70)0.65 (0.05 to 1.25).96
Ocular HOA iTrace (RMS, μm)0.11 (0.05 to 0.23)0.15 (0.02 to 0.46).002
Ocular SA iTrace (μm)0.01 (−0.049 to 0.08)0.03 (−0.130 to 0.10).10
Ocular coma iTrace (RMS, μm)0.06 (0.01 to 0.20)0.09 (0.01 to 0.36).006

Comparison of Preoperative and Postoperative Outcomes in the WFG LASIK Groupa

ParameterPreoperative1 Month Postoperative3 Months PostoperativePbPc
UDVA (logMAR)1.2 (0.6 to 1.5)−0.1 (−0.1 to 0)−0.1 (−0.1 to 0)< .0001< .0001
CDVA (logMAR)−0.1 (−0.1 to 0)−0.1 (−0.1 to 0)−0.1 (−0.1 to 0).08.08
Scan diameter on iTrace (mm)3.80 (2.90 to 4.00)3.50 (2.90 to 4.00)3.50 (2.90 to 4.00).11.11
K1 (D)43.65 (41.40 to 47.20)40.30 (35.10 to 43.40)40.3 (35.00 to 43.70)< .0001< .0001
K2 (D)44.80 (42.40 to 47.80)40.80 (35.80 to 44.50)40.95 (35.90 to 44.70)< .0001< .0001
Kmean (D)44.25 (42.00 to 47.50)40.55 (35.40 to 44.00)40.70 (35.50 to 44.10)< .0001< .0001
Minimum corneal thickness (μm)526 (487 to 561)450.5 (398 to 507)454.5 (411 to 514)< .0001< .0001
Ocular surface discomfort index6.25 (2.1 to 8.3)8.33 (2.0 to 24.7)10.41 (2.0 to 29.5).33.37
Front LOA Pentacam (RMS, μm)0.49 (0.15 to 1.51)0.50 (0.11 to 1.10)0.55 (0.16 to 0.99).52.55
Front HOA Pentacam (RMS, μm)0.09 (0.03 to 0.18)0.15 (0.06 to 0.30)0.15 (0.06 to 0.26)< .0001< .0001
Front SA Pentacam (μm)0.04 (−0.025 to 0.08)0.02 (−0.087 to 0.13)0.03 (−0.019 to 0.1).01.03
Front coma Pentacam (RMS, μm)0.064 (0.013 to 0.129)0.11 (0.006 to 0.293)0.130 (0.034 to 0.250).0009.0001
Front LOA iTrace (RMS, μm)0.28 (0.07 to 1.35)0.22 (0.06 to 0.56)0.23 (0.05 to 0.51).0008.0005
Front HOA iTrace (RMS, μm)0.07 (0.02 to 0.44)0.08 (0.02 to 0.31)0.09 (0.02 to 0.39)1.00.85
Front SA iTrace (μm)0.04 (−0.003 to 0.10)0.03 (−0.009 to 0.13)0.02 (−0.01 to 0.10).04.019
Front coma iTrace (RMS, μm)0.05 (0 to 0.21)0.06 (0.008 to 0.23)0.07 (0 to 0.36).25.28
Ocular LOA iTrace (RMS, μm)2.57 (1.25 to 4.69)0.47 (0.09 to 1.86)0.60 (0.05 to 1.70)< .0001< .0001
Ocular HOA itrace (RMS, μm)0.12 (0.07 to 0.28)0.11 (0.04 to 1.09)0.11 (0.05 to 0.23).31.10
Ocular SA iTrace (μm)0.03 (−0.049 to 0.44)0.01 (−0.038 to 0.10)0.01 (−0.049 to 0.08).58.01
Ocular coma iTrace (RMS, μm)0.06 (0.005 to 0.15)0.06 (0.01 to 0.92)0.06 (0.01 to 0.20).32.85

Comparison of Preoperative and Postoperative Outcomes in the SMILE Groupa

ParameterPreoperative1 Month Postoperative3 Months PostoperativePbPc
UDVA (logMAR)1.3 (0.5 to 1.8)0 (−0.1 to 0.1)0 (−0.1 to 0.1)< .0001< .0001
CDVA (logMAR)0 (0 to 0.2)0 (−0.1 to 0.1)0 (−0.1 to 0.1)< .0001< .00001
Scan diameter on iTrace (mm)3.95 (2.30 to 4.00)3.60 (2.00 to 4.00)3.95 (2.10 to 5.00).051.94
K1 (D)43.80 (39.70 to 46.40)40.30 (32.30 to 44.20)40.45 (32.40 to 44.20< .0001< .0001
K2 (D)44.70 (40.40 to 48.20)41.00 (33.10 to 44.80)41.10 (33.50 to 44.70)< .0001< .0001
Kmean (D)44.25 (40.20 to 47.30)40.50 (32.70 to 44.30)40.75 (33.00 to 44.20)< .0001< .0001
Minimum corneal thickness (μm)513.5 (475 to 575)442 (385 to 524)446 (400 to 529)< .0001< .0001
Ocular surface discomfort index11.46 (7.0 to 28.7)12.5 (8.33 to 22.9)8.33 (4.2 to 14.29).91.19
Front LOA Pentacam (RMS, μm)0.54 (−0.305 to 0.91)0.50 (0.14 to 1.01)0.52 (0.12 to 0.94).62.88
Front HOA Pentacam (RMS, μm)0.10 (−0.08 to 0.16)0.14 (0.07 to 0.33)0.16 (0.08 to 0.37)< .0001< .0001
Front SA Pentacam (μm)0.04 (−0.095 to 0.09)0.002 (−0.075 to 0.09)−0.001 (−0.076 to 0.10)< .0001< .0001
Front coma Pentacam (RMS, μm)0.064 (0.021 to 0.134)0.115 (0.026 to 0.30)0.130 (0.017 to 0.34)< .0001< .0001
Front LOA iTrace (RMS, μm)0.37 (0.02 to 0.87)0.31 (0.04 to 0.77)0.43 (0.05 to 0.84).44.81
Front HOA iTrace (RMS, μm)0.09 (0.02 to 0.22)0.12 (0.03 to 0.67)0.16 (0.04 to 0.61).0052< .0001
Front SA iTrace (μm)0.05 (0 to 0.10)0.04 (0 to 0.93)0.06 (−0.013 to 0.16).83.13
Front coma iTrace (RMS, μm)0.05 (0 to 0.18)0.07 (0.01 to 0.42)0.10 (0.02 to 0.55).0079< .0001
Ocular LOA iTrace (RMS, μm)2.61 (0.09 to 4.97)0.55 (0.05 to 1.29)0.65 (0.05 to 1.25)< .0001< .0001
Ocular HOA iTrace (RMS, μm)0.14 (0.02 to 2.20)0.11 (0.04 to 1.09)0.15 (0.02 to 0.46).02.91
Ocular SA iTrace (μm)0.02 (−0.050 to 0.17)0.02 (−0.091 to 0.23)0.03 (−0.130 to 0.10).37.42
Ocular coma iTrace (RMS, μm)0.07 (0.01 to 0.44)0.06 (0.01 to 0.93)0.09 (0.01 to 0.36).77.03
Authors

From the Division of Cornea and Refractive Services, Narayana Nethralaya, Bangalore, India (RS, HM, CN, AS, PK, TG) and Imaging, Biomechanics and Mathematical Modeling Solutions Lab (ASR), Narayana Nethralaya Foundation, Bangalore, India.

The authors have no financial or proprietary interest in the materials presented herein.

Supported by Abbott Medical Optics.

AUTHOR CONTRIBUTIONS

Study concept and design (RS, HM, ASR); data collection (RS, HM); analysis and interpretation of data (CN, AS, PK, TG, ASR); writing the manuscript (CN, AS, PK, TG, ASR); critical revision of the manuscript (RS, HM); statistical expertise (ASR)

Correspondence: Abhijit Sinha Roy, PhD, Narayana Nethralaya, #258A Hosur Road, Bommasandra, Bangalore 560100, India. E-mail: asroy27@yahoo.com

Received: March 02, 2018
Accepted: May 25, 2018

10.3928/1081597X-20180607-02

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