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ORIGINAL ARTICLE
mall incision lenticule extraction (SMILE) is a fem-
tosecond laser-based technique for the correction of
refractive errors that has gained popularity recent-
ly.1 This technique has been suggested to be an alternative to
LASIK for the correction of myopia, with some advantages.1
Because the SMILE technique is an all-in-one femtosecond
laser procedure, the complications associated with flap cut-
ting are avoided.2 Furthermore, because there is no superficial
cut, the impact on the subbasal nerve plexus is minor, with
less incidence of postoperative dry eye signs and symptoms in
the initial postoperative period.3-9 However, the benefit of the
SMILE technique over LASIK in terms of postoperative visual
acuity, refraction, and visual quality is not clear.10
Several comparative studies of the visual, refractive, con-
trast sensitivity, and aberrometric outcomes obtained with
SMILE and LASIK have been conducted.11-16 Most of them
reported no significant differences among techniques in vi-
sual and refractive outcomes. However, the trends in visual
quality outcomes and aberrometry are contradictory when all
of these studies are compared.11,12,14-16 Differences in sample
size, magnitude of refractive correction, clinical procedures,
and even in the surgical procedure may account for such dis-
crepancies. One common feature of all of these comparative
studies is that they compared SMILE and noncustomized fem-
tosecond laser-assisted LASIK. Only Zhang et al.17 evaluated
and compared the outcomes of SMILE with those obtained
after wavefront-guided (WFG) LASIK in eyes with moderate
S
ABSTRACT
PURPOSE: To compare the clinical outcomes of small in-
cision lenticule extraction (SMILE) and wavefront-guided
LASIK (WFG LASIK) in eyes with low and moderate myopia.
METHODS: This was a prospective, comparative study
enrolling 110 eyes with low and moderate myopia
(spherical equivalent ≤ 6.00 diopters [D]). Two groups
were differentiated according to the surgical technique
used: the WFG LASIK group included 51 eyes (51 pa-
tients) undergoing WFG LASIK using the STAR S4IR
excimer laser and the iDesign aberrometer (Abbott
Medical Optics, Abbott Park, IL) and the SMILE group in-
cluded 59 eyes (59 patients) undergoing SMILE with the
VisuMax platform (Carl Zeiss Meditec, Jena, Germany).
Visual, refractive, aberrometric, and contrast sensitivity
outcomes were evaluated during a 6-month follow-up.
RESULTS: Mean efficacy index was 0.92 ± 0.11 and
1.12 ± 0.17 in the SMILE and WFG LASIK groups, re-
spectively (P < .001). Postoperative spherical equiva-
lent was within ±0.50 D in 81.54% and 98% of eyes
in the SMILE and WFG LASIK groups (P < .001), and
postoperative cylinder was 0.50 or below in 84.7% and
100% of eyes, respectively (P = .038). Mean safety
index was 0.98 ± 0.08 and 1.20 ± 0.14 in the SMILE
and WFG LASIK groups (P < .001), with losses of lines
of corrected distance visual acuity in 6.8% and 0.0%
of eyes, respectively. Higher increase in higher order (P
< .001) and coma (P < .001) root mean square and
higher decrease in contrast sensitivity for 6, 12, and 18
cycles/degree (P ≤ .001) were observed after SMILE.
CONCLUSIONS: SMILE and WFG LASIK are efficacious
and safe procedures for the correction of low and mod-
erate myopia, but WFG LASIK allows a more predictable
outcome and better aberrometric control.
[J Refract Surg. 2017;33(5):298-304.]
From the Ophthalmology Department, Tanta University, Tanta, Egypt
(MAK, AG); Horus Vision Correction Center, Alexandria, Egypt (MAK); the
Ophthalmology Department, Alexandria University, Alexandria, Egypt (MSS);
the Ophthalmology Department, Ein Shams University, Cairo, Egypt (MGA);
and the Department of Optics, Pharmacology and Anatomy, University of
Alicante, Alicante, Spain (DPP).
Submitted: August 22, 2016; Accepted: January 25, 2017
Dr. Khalifa received an unrestricted educational grant from AMO Germany
GmbH. The remaining authors have no financial or proprietary interest in the
materials presented herein.
Correspondence: Mounir A. Khalifa, MD, PhD, Ophthalmology Department,
Tanta University, El-Geish St., Tanta, El-Gharbia Governorate, Egypt. E-mail:
mounir.khalifa100@gmail.com
doi:10.3928/1081597X-20170222-01
Comparative Analysis of the Clinical
Outcomes of SMILE and Wavefront-Guided
LASIK in Low and Moderate Myopia
Mounir A. Khalifa, MD, PhD; Ahmed Ghoneim, MD, PhD; Mohamed Shafik Shaheen, MD, PhD;
Mohamed G. Aly, MD, PhD; David P. Piñero, PhD
299
Journal of Refractive Surgery • Vol. 33, No. 5, 2017
SMILE and WFG LASIK Outcomes/Khalifa et al
to high myopic astigmatism, with a better astigmatic
outcome achieved with the WFG procedure. The aim
of the current study was to evaluate and compare the
visual, refractive, contrast sensitivity, and ocular aber-
rometric outcomes of SMILE and WFG LASIK in eyes
with low and moderate myopia with or without myo-
pic astigmatism.
PATIENTS AND METHODS
Patients
This study was a randomized, prospective, con-
secutive, comparative, and multicenter clinical trial
performed at Horus Vision Correction Centre to evalu-
ate the clinical outcomes of SMILE with the VisuMax
platform (Carl Zeiss Meditec, Jena, Germany) and
WFG LASIK with the STAR S4IR excimer laser com-
bined with the iDesign system for treatment calcula-
tion (Abbott Medical Optics, Santa Ana, CA) in 110
eyes with low and moderate myopia or myopia with
or without astigmatism. Although all surgeries were
bilateral, only information from the right eye of each
patient was included for data analysis to avoid the in-
terference in such analysis of the correlation that of-
ten exists between the two eyes of the same person.
Inclusion criteria for the study were myopia and/or
myopic astigmatism with spherical equivalent of -6.00
diopters (D) or less, patients requiring spectacle inde-
pendence and seeking a laser refractive surgery solu-
tion, and no previous ocular surgery or active ocular
disease. Exclusion criteria included myopic spheri-
cal equivalent of more than -6.00 D, hyperopic astig-
matism, unstable refraction for the past 12 months,
residual corneal bed thickness less than 300 µm, dry
eye, active ocular pathology, media opacities, previous
intraocular or corneal surgery, history of herpetic kera-
titis, immunodeficiency, systemic connective tissue
diseases, insulin-dependent diabetes mellitus, clinical
or subclinical corneal ectatic disease, history of or sus-
pected glaucoma, iris irregularities, and pregnancy or
breastfeeding. The study received approval from the
Horus Vision Correction Centre Ethics Committee. Pa-
tients were informed about the surgery and the clinical
study, and provided informed consent to participate
in it in accordance with the tenets of the Declaration
of Helsinki.
examination Protocol
Soft and rigid gas permeable contact lens wearers were
asked to remove their lenses at least 1 and 3 weeks be-
fore the preoperative examination, respectively, to avoid
the interference in the preoperative data of any contact
lens–related corneal warpage. A complete preoperative
ophthalmological examination was performed in all
cases, including measurement of uncorrected (UDVA)
and corrected (CDVA) distance visual acuity, manifest
refraction, slit-lamp anterior segment examination, cor-
neal topography and pachymetry with the Pentacam HR
system (Oculus Optikgeräte GmbH, Wetzlar, Germany),
applanation tonometry, contrast sensitivity measure-
ment (CVS-1000; VectorVision, Greenville, OH) under
mesopic conditions (3 cd/m2), ocular aberrometric analy-
sis with the iDesign system (Abbott Medical Optics), and
funduscopy. In the aberrometric analysis, the magnitude
of the root mean square (RMS) for higher order aberra-
tions (HOAs), primary coma, and trefoil, as well as the
magnitude of primary spherical aberration for a pupil ap-
erture of 5 mm, were calculated and recorded.
Clinical examinations were performed at 1 day and
1, 3, and 6 months after surgery. These postoperative
examinations included UDVA and CDVA measure-
ment, manifest refraction, biomicroscopic examina-
tion, and topographic analysis. At the last postopera-
tive visit, contrast sensitivity and ocular aberrations
were also evaluated.
surgery
SMILE was performed by a surgeon experienced
in this technique (AG) in the Ellite Vision Correc-
tion Centre, WFG LASIK surgeries were performed by
a surgeon experienced in this technique (MK) in the
Horus Vision Correction Centre, and follow-up was
done by an independent experienced practitioner
(MSS). Although surgeries were performed in different
centers, patient recruitment and follow-up examina-
tions were conducted in the same clinic (Horus Vision
Correction Centre). In the WFG LASIK group, corneal
flaps were created first using the M2 microkeratome
(Moria, Antony, France), with an intended flap thick-
ness of 110 µm. After flap lifting, the laser ablation cal-
culated according to the iDesign System measurement
was applied using the STAR S4IR excimer laser. In all
patients, iris registration and Fourier reconstruction of
the wavefront were performed and applied using the
Variable Spot Scanning of the STAR S4IR excimer la-
ser. Treatments were programmed in all cases with a
6-mm optical zone and a total ablation zone of 8 mm,
assuming a refractive target of emmetropia.
In the SMILE group, suction was applied after
checking that the centration was adequate (ring of the
touch zone concentric with the margin of the cone
and near to the pupil center). This was followed by
the creation of the posterior surface of the lenticule
from periphery to center (optical zone of 6.5 mm) fol-
lowed by transition in the peripheral optical zone,
the creation of the anterior surface of the lenticule
from center to periphery, and the performance of a
300 Copyright © SLACK Incorporated
SMILE and WFG LASIK Outcomes/Khalifa et al
peripheral incision of 2 mm with 30° of angle for pos-
terior lenticule extraction at 70°. Laser configuration
parameters were repetition rate of 500 kHz, spot dis-
tance of 4.50 µm for the lenticule and 2 µm for its
border, and pulse energy level of 30 (approximately
150 nJ). After laser treatment, the patient was moved
to the surgical microscope for the second part of the
procedure, which involved the delineation of the
front and back lenticule surfaces, their separation by
moving the instrument back and forth using a blunt
circular tip, and lenticule extraction with forceps.
In both groups, standard topical postoperative treat-
ment was administered to all patients, consisting of a
combination of dexamethasone and tobramycin four
times a day during 1 week. Also, patients were in-
structed to use an artificial tear solution at least every
2 hours the day after the surgery and at least four times
a day for 1 month.
Data analysis
Statistical analyses were performed with a commer-
cially available software package (SPSS for Mac, ver-
sion 20.0; IBM Corporation, Armonk, NY). Normality
of data samples was evaluated by the Kolmogorov–
Smirnov test. The Student’s t test for unpaired data
was used for comparisons between groups when
parametric analysis was possible, whereas the Mann–
Whitney test was applied to assess the significance
of such differences when parametric analysis was
not possible. For the analysis of differences between
preoperative and postoperative visits in each group,
the Student’s t test for paired data or the Wilcoxon
ranked sum test were used, respectively, depending
on whether the samples were distributed normally or
not. For all statistical tests, a P value of less than .05
was considered statistically significant. Finally, the
efficacy index was calculated as the ratio of the post-
operative UDVA to the preoperative CDVA, and the
safety index was calculated as the ratio of the post-
operative CDVA to the preoperative CDVA.18 The Al-
pins vector analysis method was used for the analysis
of the astigmatic changes occurring after surgery.19,20
The following vectors were determined and evalu-
ated: target induced astigmatism (TIA) as the vector
of intended change in cylinder for each treatment,
surgically induced astigmatism (SIA) as the vector of
the real change achieved, and difference vector as the
additional astigmatic change that would enable the
initial surgery to achieve its intended target. Addi-
tionally, the magnitude of error (difference between
the magnitude of SIA and TIA) and the angle of error
(angle described by the vectors of SIA and TIA) were
calculated.
RESULTS
Visual and refractive outcomes are shown in Figure 1.
A total of 59 eyes of 59 patients with a mean age of
26.7 ± 5.8 years (range: 20 to 55 years) underwent WFG
LASIK (WFG LASIK group), and a total of 51 eyes of
51 patients with a mean age of 26.1 ± 7.2 years (range:
20 to 55 years) underwent SMILE for the correction of
myopia with or without astigmatism (SMILE group).
No statistically significant differences in age, sex, or
manifest refraction were found among groups preop-
eratively (P ≥ .118).
Table 1 summarizes the visual and refractive out-
comes in the WFG LASIK and SMILE groups at 6
months after surgery. Statistically significant differ-
ences in UDVA and CDVA were found preoperative-
ly and postoperatively between the WFG LASIK and
SMILE groups (P ≤ .006). Specifically, significantly
better preoperative and postoperative UDVA was pres-
ent in the WFG LASIK group compared to the SMILE
group (P ≤ .006). However, although preoperative
CDVA was significantly better in the SMILE group
compared to the WFG LASIK group (P < .001), post-
operative CDVA was significantly better in the WFG
LASIK group (P < .001). Likewise, lower magnitude
of manifest cylinder (P = .010) and spherical equiva-
lent (P < .001) were found postoperatively in the WFG
LASIK group compared to the SMILE group. A total of
81.54% and 98% of eyes had a 6-month postoperative
spherical equivalent within ±0.50 in the SMILE and
WFG LASIK groups, respectively (Figure 1) (P < .001).
A significant correlation was found between attempted
and achieved spherical equivalent correction in both
the SMILE (r = 0.94, P < .001) and WFG LASIK (r =
0.99, P < .001) groups, although a stronger correlation
was found in the WFG LASIK group (Figure 1). Re-
garding the cylinder, a total of 84.7% and 100% of eyes
had 6-month postoperative values of 0.50 D or below
in the SMILE and WFG LASIK groups, respectively
(Figure 1) (P = .038). Concerning the vector analysis of
astigmatic changes, statistically significant differences
between the SMILE and WFG LASIK groups were ob-
served at 6 months postoperatively in TIA (1.11 ± 0.73
and 1.37 ± 0.65, P = .030), SIA (1.05 ± 0.73 and 1.32 ±
0.61, P = .010), and difference vector (0.30 ± 0.32 and
0.16 ± 0.22, P = .010). No significant differences among
groups were found in magnitude of error (-0.05 ± 0.32
and -0.05 ± 0.19, P = .974) and angle of error (2.63 ±
13.26 and 1.89 ± 5.36, P = .874).
Mean efficacy index was 0.92 ± 0.11 and 1.12 ±
0.17 in the SMILE and WFG LASIK groups, respec-
tively (P < .001). A total of 77.97% and 90.20% of
eyes achieved a postoperative UDVA of 0.00 logMAR
or better (20/20 Snellen) in the SMILE and WFG
301
Journal of Refractive Surgery • Vol. 33, No. 5, 2017
SMILE and WFG LASIK Outcomes/Khalifa et al
LASIK groups, respectively (Figure 1) (P = .021).
Mean safety index was 0.98 ± 0.08 and 1.20 ± 0.14 in
the SMILE and WFG LASIK groups, respectively (P <
.001). Losses of one line of CDVA occurred in 6.8%
and 0% of eyes in the SMILE and WFG LASIK groups,
respectively (Figure 1) (P < .001).
Table A (available in the online version of this ar-
ticle) summarizes the ocular aberrometric outcomes in
the WFG LASIK and SMILE groups. Because there were
significant differences among groups preoperatively,
ocular aberrometric changes were compared among
groups instead of postoperative values. As shown, sig-
nificantly higher increases in HOA (P < .001) and pri-
mary coma RMS (P < .001) were observed in the SMILE
group compared to the WFG LASIK group. Change in
mesopic contrast sensitivity with surgery was also
analyzed in each group and compared (Table B, avail-
able in the online version of this article). Significantly
higher decreases of contrast sensitivity were found in
the SMILE group compared to the WFG LASIK group
Figure 1. Visual and refractive outcomes. (A) Distribution of 6-month postoperative uncorrected distance visual acuity (UDVA) compared to the distribu-
tion of preoperative corrected distance visual acuity (CDVA). (B) Distribution of changes in lines of CDVA at 6 months postoperatively. (C) Scattergram
showing the relationship among attempted and achieved correction of spherical equivalent (SE) at 6 months postoperatively for the (C) small incision
lenticule extraction (SMILE) and (D) wavefront-guided LASIK (WFG LASIK) groups. (E) Distribution of 6-month postoperative SE. (F) Distribution of
6-month postoperative cylinder. D = diopters
302 Copyright © SLACK Incorporated
SMILE and WFG LASIK Outcomes/Khalifa et al
for the spatial frequencies of 6 (P = .001), 12 (P = .001),
and 18 (P < .001) cycles/degree.
DISCUSSION
In the current study, the comparison of the out-
comes obtained in eyes with -6.00 D or less of myopia
after undergoing refractive correction with SMILE and
WFG LASIK revealed the presence of significant differ-
ences among techniques. Specifically, there were dif-
ferences in terms of refractive predictability, efficacy,
and safety, with a better outcome achieved with WFG
LASIK. Likewise, a lower increase of HOA and prima-
ry coma RMS and lower decrease in mesopic contrast
sensitivity were found in eyes undergoing WFG LASIK
compared to those undergoing SMILE.
Lin et al.16 compared the outcomes of 60 eyes with
a mean spherical equivalent of -5.13 ± 1.75 D operated
on with the SMILE procedure with those obtained in
51 eyes with a mean spherical equivalent of -5.58 ±
2.41 D treated with femtosecond laser–assisted LASIK.
These authors found comparable outcomes in terms
of visual and refractive outcomes, but they obtained
a lower induction rate of HOA RMS with SMILE than
with LASIK.16 However, these authors did not use
WFG ablation profiles to optimize the LASIK ablation
profile. Furthermore, these authors found a more sig-
nificant induction of primary coma with SMILE com-
pared to LASIK,16 which seemed to be related to the
presence of mild levels of treatment decentration, as
suggested and analyzed by Li et al.21 Specifically, the
latter authors confirmed by means of multivariate asso-
ciation analysis that there was a relationship between
the magnitude of the horizontal decentration and the
induced horizontal coma after SMILE.21
Ganesh and Gupta15 also compared SMILE and stan-
dard (non-WFG) femtosecond laser–assisted LASIK
and obtained a superiority in terms of aberrometric
control and preservation of visual quality of SMILE
over LASIK. In contrast, Liu et al.12 recently reported
comparable visual outcomes with SMILE and non-
WFG LASIK in eyes with moderate to high myopia
and myopic astigmatism, with a trend toward a lower
induction of spherical aberration (6-mm pupil aper-
ture) at 6 months postoperatively with SMILE. In our
sample, no significant differences in terms of changes
in spherical aberration for a 5-mm pupil aperture were
found between SMILE and WFG LASIK. The inclusion
of cases of high myopia in the study of Liu et al.12 and
the use of non-WFG ablation profiles with LASIK may
have accounted for our different finding in terms of
spherical aberration change. Therefore, according to
our outcomes, WFG LASIK seems to have the ability
to better control the aberrometric change with surgery
than SMILE in eyes with low to moderate myopia or
myopic astigmatism.
Zhang et al.17 recently demonstrated that the cor-
rection of moderate astigmatism after WFG LASIK
was somewhat more accurate than with SMILE. In our
sample of moderate myopia, postoperative cylinder
of 0.50 D or less was found in 84.7% and 100.0% of
eyes undergoing SMILE and WFG LASIK, respectively.
Therefore, a trend to obtain a suboptimal astigmatic
correction was observed in low to moderate myopic
eyes undergoing SMILE, which is consistent with the
results of previous studies.13,22,23 This was confirmed
with the Alpins vector analysis, which revealed a sig-
nificantly higher difference vector in the SMILE group
and a larger variability in the magnitude of error. Chan
et al.13 also showed in a comparative study of SMILE
and standard LASIK that SMILE provided a less favor-
TABLE 1
Preoperative and 6-Month Postoperative Visual and Refractive Dataa
Preoperative 6-Month Postoperative
Parameter SMILE WFG LASIK PSMILE WFG LASIK P
UDVA (logMAR) 0.87 ± 0.29,
1.00 (0.52 to 1.30)
0.71 ± 0.34,
0.70 (0.40 to 2.00)
.001 0.03 ± 0.08,
0.00 (-0.08 to 0.30)
-0.01 ± 0.06,
0.00 (-0.08 to 0.10)
.006
Manifest sphere (D) -3.17 ± 1.01,
-3.00 (-5.00 to -1.75)
-2.98 ± 1.37,
-2.50 (-5.50 to -0.50)
.285 -0.20 ± 0.39,
-0.25 (-1.25 to 0.75)
-0.02 ± 0.13,
0.00 (-0.50 to 0.25)
.001
Manifest cylinder (D) -1.05 ± 0.75,
-0.75 (-2.75 to 0.00)
-1.26 ± 0.73,
-1.25 (-4.00 to 0.00)
.030 -0.30 ± 0.31,
-0.25 (-1.00 to 0.00)
-0.15 ± 0.21,
0.00 (-0.50 to 0.00)
.010
Manifest SE (D) -3.69 ± 1.17,
-3.50 (-6.00 to -2.12)
-3.61 ± 1.39,
-3.00 (-6.00 to -1.50)
.748 -0.35 ± 0.40,
-0.38 (-1.75 to 0.38)
-0.10 ± 0.14,
0.00 (-0.62 to 0.12)
< .001
CDVA (logMAR) -0.01 ± 0.04,
0.00 (-0.08 to 0.10)
0.03 ± 0.05,
0.00 (-0.08 to 0.15)
< .001 0.00 ± 0.05,
0.00 (-0.08 to 0.22)
-0.04 ± 0.05,
-0.07 (-0.08 to 0.05)
< .001
SMILE = small incision lenticule extraction; WFG = wavefront-guided; UDVA = uncorrected distance visual acuity; D = diopters; SE = spherical equivalent; CDVA
= corrected distance visual acuity
aValues are reported as mean ± standard deviation, median (range).
303
Journal of Refractive Surgery • Vol. 33, No. 5, 2017
SMILE and WFG LASIK Outcomes/Khalifa et al
able correction than LASIK in eyes with low and mod-
erate myopic astigmatism. These authors also conclud-
ed that the alignment of treatment was more variable
in SMILE, leading to a lower efficacy compared with
LASIK by 3 months postoperatively.13 Furthermore, in
our study, there was a trend to a slight myopic residu-
al refractive error affecting the efficacy achieved after
SMILE, as in other previous studies.10 Zhang et al.22
suggested according to the results of their retrospective
study that nomograms for SMILE should be adjusted
in correcting astigmatism because it tended to provide
a suboptimal correction, possibly due to axis rotation
during surgery or wound healing. We believe that one
of the reasons for the good correction of astigmatism
in the WFG LASIK group in our study is that iris reg-
istration was engaged in 100% of eyes under the laser,
which allowed for a good centration of the treatment
and avoided human errors.
In our study, besides the difference in terms of ef-
ficacy for moderate myopia, a significant difference
between SMILE and WFG LASIK was found in safety,
with more eyes losing one line of CDVA in the SMILE
group (6.8% vs 0.0%). This is consistent with the high-
er induction of HOAs and loss of contrast sensitivity
found after SMILE in our sample. However, besides
the induction of primary coma and other HOAs, the
increase in ocular scattering after SMILE may have ac-
counted for the presence of more cases of loss of one
line of CDVA with this technique compared to WFG
LASIK. Miao et al.24 reported a postoperative tem-
porary increase of the ocular scattering index after
SMILE. Likewise, Agca et al.25 demonstrated in a com-
parative study using confocal microscopy that SMILE
resulted in increased backscattered light intensity in
the anterior stroma when compared with femtosecond
laser–assisted LASIK during the first 6 postoperative
months. Besides changes in the transparency of the in-
terface, the presence of significantly higher amounts
of microdistortions of Bowman’s layer after SMILE in
the initial postoperative period compared to LASIK
seems to also play a role in the increase in corneal light
scattering with the SMILE technique.26 Future studies
should be conducted to confirm whether changes in
energy settings of the femtosecond laser used in the
SMILE technique might contribute to a lower induc-
tion of corneal backscatter and a faster visual recovery
in the initial postoperative period.
The results obtained in our study with the SMILE
technique were similar to those obtained by some au-
thors and worse than those reported by others.10 In-
deed, a significant variability in the outcomes reported
for the SMILE technique has been observed in the peer-
reviewed literature, which may be attributed to many
factors, including differences in terms of clinical ex-
amination and surgical protocols, use of different no-
mograms and versions of the surgical equipment, dif-
ferent ranges of myopic correction, and variations in
the level of expertise of the surgeon.10 For this reason,
comparative randomized studies comparing SMILE
with the other available refractive techniques are nec-
essary to know the real benefit of this technique over
the previous technique.
SMILE and WFG LASIK are efficacious and safe
procedures for the correction of low and moderate
myopia or myopic astigmatism, but WFG LASIK pro-
vides a more predictable outcome, better aberrometric
control, and better preservation of visual quality. Op-
timizations in the algorithms used for the calculation
of the lenticule size to extract according to the refrac-
tive error are necessary with the SMILE technique to
improve the refractive predictability even more. The
development of a future WFG SMILE technique with
automatic axial and torsional registration would allow
better astigmatic correction and an optimization of the
aberrometric changes induced with the surgery and
consequently of the visual quality outcomes.
AUTHOR CONTRIBUTIONS
Study concept and design (MAK, MSS, DPP); data collection
(MAK, AG, MGA); analysis and interpretation of data (MAK, AG,
MSS, DPP); writing the manuscript (DPP); critical revision of the
manuscript (MAK, AG, MSS, MGA, DPP); statistical expertise (MAK,
DPP); administrative, technical, or material support (MAK, AG,
MSS, MGA, DPP); supervision (MAK, AG, MSS, DPP)
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TABLE A
Preoperative and 6-Month Postoperative Ocular Aberrometric Data (5-mm Pupil)a
Preoperative 6-Month Postoperative
Parameter SMILE WFG LASIK PSMILE WFG LASIK P
HOA RMS (µm) 0.47 ± 0.14,
0.43 (0.29 to 0.85)
0.39 ± 0.18,
0.38 (0.01 to 0.73)
.007 0.73 ± 0.16,
0.65 (0.48 to 1.16)
0.50 ± 0.19,
0.48 (0.28 to 1.19)
< .001
Coma RMS
(µm)
0.12 ± 0.04,
0.11 (0.01 to 0.20)
0.16 ± 0.09,
0.14 (0.04 to 0.34)
.017 0.23 ± 0.09,
0.22 (0.08 to 0.42)
0.15 ± 0.06,
0.15 (0.01 to 0.31)
< .001
Trefoil (µm) 0.18 ± 0.08,
0.16 (0.04 to 0.34)
0.10 ± 0.06,
0.07 (0.02 to 0.22)
< .001 0.19 ± 0.11,
0.21 (0.01 to 0.32)
0.13 ± 0.05,
0.14 (0.03 to 0.22)
.003
SA (µm) 0.03 ± 0.06,
0.01 (-0.08 to 0.18)
0.02 ± 0.10,
0.02 (-0.21 to 0.39)
.346 0.04 ± 0.08,
0.04 (-0.09 to 0.19)
0.01 ± 0.07,
0.02 (-0.12 to 0.15)
.048
Changes in HOA
RMS
– – – 0.25 ± 0.18,
0.21 (-0.10 to 0.72)
0.11 ± 0.21,
0.07 (-0.26 to 1.03)
< .001
Change in coma
RMS
– – – 0.12 ± 0.10,
0.09 (-0.09 to 0.35)
-0.01 ± 0.10,
-0.02 (-0.26 to 0.23)
< .001
Change in trefoil
RMS
– – – 0.02 ± 0.04,
0.03 (-0.09 to 0.08)
0.03 ± 0.07,
0.03 (-0.08 to 0.15)
.614
Change in SA – – – 0.01 ± 0.07,
0.01 (-0.07 to 0.21)
0.00 ± 0.12,
0.01 (-0.43 to 0.17)
.990
SMILE = small incision lenticule extraction; WFG = wavefront-guided; HOA = higher order aberrations; RMS = root mean square; SA = spherical aberration
aValues are reported as mean ± standard deviation, median (range).
TABLE B
Preoperative and 6-Month Postoperative Contrast Sensitivity
Data Measured Under Mesopic Conditionsa
Preoperative Postoperative
Parameter SMILE WFG LASIK PSMILE WFG LASIK P
CS 3 cpd 1.96 ± 0.13,
2.06 (1.60 to 2.06)
1.91 ± 0.18,
2.06 (1.60 to 2.06)
.253 1.97 ± 0.15,
2.06 (1.46 to 2.06)
1.88 ± 0.18,
1.90 (1.46 to 2.06)
.003
CS 6 cpd 1.99 ± 0.12,
1.95 (1.81 to 2.11)
1.90 ± 0.16,
1.95 (1.65 to 2.11)
.002 1.92 ± 0.16,
1.95 (1.36 to 2.11)
1.90 ± 0.18,
1.81 (1.65 to 2.11)
.450
CS 12 cpd 1.73 ± 0.23,
1.78 (1.18 to 1.93)
1.60 ± 0.12,
1.63 (1.48 to 1.93)
< .001 1.60 ± 0.21,
1.63 (1.18 to 1.93)
1.63 ± 0.15,
1.63 (1.34 to 1.78)
.728
CS 18 cpd 1.43 ± 0.23,
1.36 (0.78 to 1.66)
1.28 ± 0.14,
1.23 (0.90 to 1.52)
< .001 1.28 ± 0.20,
1.36 (0.60 to 1.52)
1.28 ± 0.11,
1.23 (1.08 to 1.52)
.151
Change in CS 3 cpd – – – 0.01 ± 0.14,
0.00 (-0.30 to 0.16)
-0.03 ± 0.12,
0.00 (-0.30 to 0.16)
.177
Change in CS 6 cpd – – – -0.07 ± 0.15,
-0.14 (-0.59 to 0.30)
0.00 ± 0.12,
0.00 (-0.16 to 0.16)
.001
Change in CS 12 cpd – – – -0.13 ± 0.26,
0.00 (-0.60 to 0.30)
0.03 ± 0.15,
0.00 (-0.29 to 0.30)
.001
Change in CS 18 cpd – – – -0.15 ± 0.15,
-0.14 (-0.46 to 0.13)
0.00 ± 0.12,
0.00 (-0.16 to 0.33)
< .001
SMILE = small incision lenticule extraction; WFG = wavefront-guided; CS = contrast seneitivity; cpd = cycles per degree
aValues are reported as mean ± standard deviation, median (range).
