Corneal Asymmetry and Ocular Higher-Order Aberrations after Small Incision Lenticule Extraction for Moderate-to-High Myopia in One Year

doi:10.21203/rs.3.rs-3238937/v1

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Corneal Asymmetry and Ocular Higher-Order Aberrations after Small Incision Lenticule Extraction for Moderate-to-High Myopia in One Year

https://doi.org/10.21203/rs.3.rs-3238937/v1

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Background

To evaluate the relationships between the magnitudes of corneal asymmetry and induced ocular higher-order aberrations (HOAs) after small-incision lenticule extraction (SMILE) for moderate-to-high myopia.

Methods

Sixty-six eyes of 66 patients who underwent SMILE were divided into two groups: the high (SE ≥ -6.0 D, n = 27, Group H) and moderate (-3.0 D ≤ SE < -6.0 D, n = 39, Group M) myopia groups. Using Fourier harmonic analysis, the spherical component (SC), regular astigmatism (RA), asymmetry, and higher-order irregularity (HOI) were obtained from videokeratography data. Visual acuity, manifest refraction, and ocular HOAs were assessed at baseline and 3, 6, and 12 months postoperatively. The relationships between Fourier components and ocular HOAs were assessed.

Results

In both groups, vertical coma, horizontal coma, spherical aberration, total higher-order aberrations (tHOAs), and asymmetry of the anterior corneal surface increased postoperatively (from 3 to 12 months), while SC and RA of the anterior corneal surface decreased (all P < 0.05). More vertical coma and asymmetry of the anterior corneal surface were induced in Group H than in Group M at 3 and 6 months postoperatively (all P < 0.05). The association between preoperative asymmetry of the anterior corneal surface and preoperative spherical aberration was significant in both groups (R² = 0.138, P = 0.02; R² = 0.172, P = 0.032, respectively). The asymmetry of the anterior corneal surface was correlated with vertical coma, spherical aberration, and tHOAs at 3, 6, and 12 months postoperatively in both groups (all R² > 0.2, all P < 0.05).

Conclusions

The visual quality after SMILE was associated with the asymmetry of the anterior corneal surface for moderate-to-high myopia in one year.

Small incision lenticule extraction

corneal asymmetry

Fourier harmonic analysis

higher-order aberrations

myopia

Small-incision lenticule extraction (SMILE) is a safe, efficient, and predictable intrastromal technique to correct moderate-to-high myopia.[1] However, previous studies have shown that the preoperative higher-order aberrations (HOAs), such as coma and spherical aberration, have increased and resulted in postoperative deterioration of optical quality.[2–4] Visual quality perceived by the patient after refractive surgery is an important determinant of overall satisfaction. The relationships between preoperative refraction,[5] angle kappa,[6] decentration,[7] and induced HOAs following SMILE have been studied earlier. Among the existing analytical tools, the Fourier analysis allows researchers and clinicians to extract information of rational optical components from complex topographic corneal images.[8] However, the correlation between the ocular wavefront aberrations and the changes in corneal topography using Fourier harmonic analysis is still unclear. Corneal asymmetry is a tilt of the cornea noted on the videokeratoscope. This axis facilitates the quantitative assessment of corneal irregularities after refractive surgery, including SMILE,[9] myopic laser in situ keratomileuses (LASIK),[10] hyperopic LASIK,[11] myopic photorefractive keratectomy (PRK),[12] cataract surgery,[13] and penetrating keratoplasty (PK).[14] To our knowledge, few studies have evaluated the relation between corneal asymmetry and ocular HOAs after SMILE.[9] Understanding the features and the associations between the morphological changes of the cornea and ocular HOAs in patients could help clinicians to evaluate the visual quality after surgery. Therefore, this study used Fourier analysis to investigate the postoperative changes of corneal asymmetry following SMILE for moderate-to-high myopia in one year.

Patients

In this retrospective study, we included 66 consecutive patients (66 eyes) who underwent SMILE surgery at the Department of Ophthalmology, Shanghai Tenth People’s Hospital, affiliated to Tongji University, from July 2017 to July 2020. The inclusion criteria were as follows: age 18–35 years, corrected distance visual acuity (CDVA) of 20/20 or better, myopic spherical correction ≥ -3.00 D with astigmatism < -3.00 D, no ocular or systemic diseases, and stable refraction for two years. Exclusion criteria included any history of ocular surgery, ocular trauma, and systemic or ocular health abnormality. The eyes were divided preoperatively into two groups according to the spherical equivalent (SE): the high myopia group (SE ≥ -6.0 D, n = 27, Group H) and the moderate group (-3.0 D ≤ SE < -6.0 D, n = 39, Group M). The present study followed the tenets of the Declaration of Helsinki and was approved by the Ethics Committee of the Shanghai Tenth People’s Hospital. All participants signed informed consents.

SMILE procedure

One surgeon (Dr. Zou) performed all surgeries using the 500 kHz VisuMax femtosecond laser system (Carl Zeiss Meditec, Jena, Germany). Preoperative medication included topical 0.5% levofloxacin (Santen Pharmaceutical Co., Ltd.) thrice daily for 3 days. The parameters for SMILE procedure were: 500 kHz repetition rate, 150 nJ pulse energy, 115 to 130 µm intended cap thickness, 5.8 to 6.8 mm optical zone, 7.6 mm cap diameter, and a 90° single-side incision with a length of 2 mm to extract the lenticule.

Examination

Before the SMILE surgery, 3, 6, and 12 months postoperatively, all patients underwent complete ophthalmic examination that included uncorrected distance visual acuity (UDVA) and CDVA, manifest refraction, slit-lamp examination, dilated fundus examination, intraocular pressure measurement by a non-contact tonometer, corneal topography using the swept-source anterior segment OCT (CASIA SS-1000, Tomey Corporation, Inc., Aichi, Japan). The wavefront aberrations were measured and analyzed for 6-mm pupil diameter with a Zywave aberrometer using a Hartmann-Shack sensor (Bausch & Lomb, US). The absolute Zernike coefficients including vertical trefoil, horizontal trefoil, vertical coma, horizontal coma, spherical aberration, and total higher-order aberrations (tHOAs) were analyzed. Using Fourier harmonic analysis program, the dioptric power of the ring i, F_i (σ), was transformed into trigonometric components of the following form:

F_i(σ) = α₀ + c₁cos1(σ − α₁) + c₂cos2(σ − α₂) + c₃ cos3(σ − α₃) + ··· + c_n cosn(σ − α_n)

In which α₀ is the spherical component (SC) of the ring, 2×c₁ is the asymmetry component, 2×c₂ is regular astigmatism (RA), and the summation of c₃ … c_n includes the higher-order irregularity components (HOI). Among these, SC and RA were corrected using a spherocylindrical lens, while asymmetry and HOI were not, representing corneal irregular astigmatism. These indices were calculated within the central 6-mm diameter zone.

Statistical analysis

One eye of each subject (the right or left) was selected by a random number schedule for statistical analysis. All data were analyzed using SPSS version 23.0 statistical software (SPSS Inc., Chicago, IL, USA). The Shapiro-Wilk test was used to test for normality. Independent t-test was used for normally distributed data and the Mann-Whitney U test for abnormally distributed data (except the gender and eye, which were compared by chi-square tests). Repeated measurement analysis was performed to assess the standardized differences in preoperative and postoperative visits at setting time points. The relationships between Fourier indices and wavefront aberrations in each group were evaluated with Spearman’s correlation analysis and the linear regression coefficient (R²). Visual acuity was converted to logarithm of the minimal angle of resolution (logMAR) for statistical analysis. P value < 0.05 was considered statistically significant.

All 66 patients (27 eyes in Group H and 39 eyes in Group M) attended the 3-month, 6-month, and 12-month follow-up examinations. The baseline characteristics of the two groups are summarized in Table 1. There were no significant preoperative differences in age (P = 0.588) and gender (P = 0.52) between the two groups. The manifest spherical equivalent (P < 0.001), manifest sphere (P < 0.001), manifest cylinder (P = 0.019), logMAR of the CDVA (P = 0.011), and ablation depth (P < 0.001) were significantly different between the two groups before surgery.

Table 1

Characteristics of the two groups.
	Group H	Group M	P
Eye (R/L)	14/13	19/20	0.802
Age (years)	26.6 ± 5.6	25.8 ± 5.3	0.588
Gender (% female)	74%	67%	0.520
CDVA (LogMAR)	-0.058 ± 0.044	-0.077 ± 0.013	0.011
Sphere (D)	-6.65 ± 0.82	-3.95 ± 0.81	< 0.001
Cylinder (D)	-1.22 ± 0.67	-0.90 ± 0.48	0.019
SE (D)	-7.26 ± 1.04	-4.40 ± 0.80	< 0.001
Ablation depth (µm)	152.22 ± 77.93	128.10 ± 96.10	< 0.001

Visual acuity and refraction

The visual and refractive outcomes of the two groups were summarized in Table 2. At 3, 6, and 12 months postoperatively, there was a significant difference in the manifest SE in both groups (P = 0.006, P < 0.001, P < 0.001, respectively). However, there was no significant difference in the LogMAR of UDVA between the two groups (P = 0.288, P = 0.172, P = 0.498, respectively). During the one-year follow-up, all eyes in both groups had a postoperative UDVA of 20/25 or better. At the last follow-up, 27 (96.3%) eyes in Group H and 38 (97.4%) eyes in Group M achieved a UDVA of 20/20. UDVA was ≥ 20/16 in 18 (66.7%) and 29 (74.4%) eyes in Group H and Group M, respectively. Twenty-five (92.6%) eyes in Group H and 37 (94.9%) eyes in Group M remained stable or gained one to two lines of CDVA. Only 2 (7.4%) eyes in Group H and 2 (5.1%) eyes in Group M lost one line, whereas none of the eyes in the two groups lost two or more lines. There was no statistical difference in the efficacy index (postoperative UDVA/preoperative CDVA) and the safety index (postoperative CDVA/preoperative CDVA) in the two groups.

Table 2

Visual and refractive outcomes of the two groups.
	Group H	Group M	P
3m Postoperative
SE (D)	-0.34 ± 0.20	-0.18 ± 0.22	0.006
UDVA (LogMAR)	-0.046 ± 0.047	-0.059 ± 0.035	0.288
Efficacy Index	0.98 ± 0.14	0.96 ± 0.07	0.608
Safety Index	1.01 ± 0.13	0.96 ± 0.15	0.300
6m Postoperative
SE (D)	-0.38 ± 0.32	-0.14 ± 0.17	< 0.001
UDVA (LogMAR)	-0.043 ± 0.054	-0.061 ± 0.034	0.172
Efficacy Index	0.97 ± 0.11	0.97 ± 0.07	0.925
Safety Index	1.00 ± 0.08	0.99 ± 0.04	0.513
12m Postoperative
SE (D)	-0.45 ± 0.24	-0.20 ± 0.24	< 0.001
UDVA (LogMAR)	-0.049 ± 0.047	-0.056 ± 0.042	0.498
Efficacy Index	0.99 ± 0.14	0.96 ± 0.08	0.512
Safety Index	1.02 ± 0.12	0.99 ± 0.04	0.288
UDVA: uncorrected distance visual acuity; CDVA: corrected distance visual acuity; SE: spherical equivalent.

Wavefront aberrations

The changes in ocular wavefront aberrations after SMILE in the two groups were displayed in Table 3. Postoperatively, the vertical coma, horizontal coma, spherical aberration, and tHOAs were increased in both groups (all P < 0.05). There was a significant decrease in horizontal trefoil in Group H after SMILE surgery (P = 0.007) with no difference in Group M. Furthermore, no differences were found in the vertical trefoil values in both groups pre-and post-SMILE surgery (P = 0.135, P = 0.907, respectively). A comparison of the changes in ocular wavefront aberrations between the two groups showed that SMILE induced more vertical coma in Group H than in Group M at 3 and 6 months postoperatively (Fig. 1, P = 0.029, P = 0.017, respectively). However, there was no difference in the changes in vertical trefoil, horizontal trefoil, horizontal coma, spherical aberration, and tHOAs between the two groups postoperatively.

Table 3

Preoperative versus postoperative ocular wavefront aberrations (m).
µ
		Preoperative	3m Postoperative	6m Postoperative	12m Postoperative	P
Group H	Vertical trefoil	0.192 ± 0.142	0.133 ± 0.089	0.200 ± 0.213	0.135 ± 0.122	0.135
	Horizontal trefoil	0.146 ± 0.109	0.089 ± 0.068	0.088 ± 0.096	0.071 ± 0.059^a	0.007
	Vertical coma	0.271 ± 0.203	0.389 ± 0.287	0.487 ± 0.337	0.434 ± 0.273	0.030
	Horizontal coma	0.099 ± 0.106	0.325 ± 0.192^a	0.312 ± 0.213^a	0.298 ± 0.198^a	< 0.001
	Spherical aberration	0.465 ± 0.205	0.632 ± 0.225	0.708 ± 0.364^a	0.647 ± 0.227^a	0.003
	tHOAs	0.541 ± 0.217	0.762 ± 0.217^a	0.822 ± 0.354^a	0.740 ± 0.240	< 0.001
Group M	Vertical trefoil	0.140 ± 0.101	0.137 ± 0.101	0.138 ± 0.105	0.129 ± 0.106	0.907
	Horizontal trefoil	0.138 ± 0.136	0.138 ± 0.096	0.131 ± 0.096	0.121 ± 0.091	0.656
	Vertical coma	0.193 ± 0.158	0.259 ± 0.187	0.261 ± 0.187	0.302 ± 0.228	0.032
	Horizontal coma	0.093 ± 0.093	0.186 ± 0.121^a	0.190 ± 0.124^a	0.187 ± 0.130^a	< 0.001
	Spherical aberration	0.373 ± 0.179	0.467 ± 0.152	0.470 ± 0.147	0.491 ± 0.180^a	0.005
	tHOAs	0.438 ± 0.176	0.540 ± 0.152^a	0.542 ± 0.146^a	0.564 ± 0.178^a	0.002
tHOAs: total higher-order aberrations; ^a vs. pre values of statistical significance (P < 0.05).

Fourier analysis

The corneal indices of the anterior and posterior corneal surface using Fourier harmonic analysis in the two groups were summarized in Table 4. In the anterior corneal surface, the mean SC and RA decreased significantly in both groups after SMILE (all P < 0.001); however, the asymmetry increased significantly (all P < 0.001). No changes were found in HOI after surgery in both groups. The comparison of the changes in Fourier parameters pre-and post-SMILE between the two groups was shown in Fig. 2. After 3 to 12 months postoperatively, the SC and asymmetry in Group H were significantly higher than in Group M (Fig. 2. A, C, all P < 0.01). However, there was no difference in RA and HOI between the two groups (Fig. 2. B, D). In the posterior corneal surface, a significant decrease was observed in the SC for both groups (both P < 0.001). There were no differences between the two groups in preoperative and postoperative RA, asymmetry, and HOI. The comparison of the changes of Fourier parameters between the two groups showed that SC was significantly decreased in Group H than in Group M 6–12 months postoperatively (Fig. 2. E, P = 0.044, P = 0.002, respectively).

Table 4

Preoperative versus postoperative Fourier parameters (D).
			Preoperative	3m Postoperative	6m Postoperative	12m Postoperative	P
Group H	Anterior	SC	48.509 ± 1.378	42.723 ± 1.722^a	42.769 ± 1.668^a	42.820 ± 1.786^a	< 0.001
		RA	0.797 ± 0.329	0.604 ± 0.219^a	0.580 ± 0.225^a	0.541 ± 0.229^ab	< 0.001
		Asymmetry	0.410 ± 0.167	1.154 ± 0.489^a	1.145 ± 0.467^a	1.147 ± 0.469^a	< 0.001
		HOI	0.164 ± 0.038	0.156 ± 0.039	0.144 ± 0.031	0.150 ± 0.035	0.179
	Posterior	SC	-6.182 ± 0.188	-6.215 ± 0.181^a	-6.219 ± 0.186^a	-6.219 ± 0.186^a	< 0.001
		RA	0.173 ± 0.057	0.172 ± 0.054	0.173 ± 0.056	0.172 ± 0.055	0.939
		Asymmetry	0.054 ± 0.030	0.056 ± 0.027	0.052 ± 0.033	0.053 ± 0.031	0.620
		HOI	0.020 ± 0.006	0.020 ± 0.005	0.020 ± 0.004	0.019 ± 0.005	0.920
Group M	Anterior	SC	47.672 ± 1.414	43.660 ± 1.659^a	43.668 ± 1.656^a	43.730 ± 1.660^a	< 0.001
		RA	0.657 ± 0.324	0.540 ± 0.268^a	0.509 ± 0.261^a	0.507 ± 0.237^a	< 0.001
		Asymmetry	0.327 ± 0.185	0.702 ± 0.332^a	0.744 ± 0.341^a	0.717 ± 0.339^a	< 0.001
		HOI	0.167 ± 0.063	0.160 ± 0.037	0.162 ± 0.045	0.150 ± 0.038	0.375
	Posterior	SC	-6.062 ± 0.224	-6.086 ± 0.232^a	-6.084 ± 0.227^a	-6.081 ± 0.227^a	< 0.001
		RA	0.165 ± 0.064	0.162 ± 0.065	0.162 ± 0.059	0.160 ± 0.061	0.517
		Asymmetry	0.046 ± 0.036	0.046 ± 0.038	0.046 ± 0.027	0.040 ± 0.027	0.378
		HOI	0.024 ± 0.020	0.024 ± 0.031	0.022 ± 0.007	0.021 ± 0.006	0.710
SC: spherical component; RA: regular astigmatism; HOI: higher-order irregularity. ^a vs. pre values of statistical significance (P < 0.05); ^b vs. 3-month values of statistical significance (P < 0.05).

Linear regression analysis

Refractive data and surgical parameters were evaluated pre- and post-SMILE to explore the relationships between ocular HOAs and the Fourier indices. As shown in Fig. 3, the asymmetry of the anterior corneal surface had a positive correlation with the vertical coma, spherical aberration, and tHOAs in both groups at 3–12 months postoperatively (all P < 0.05). The asymmetry of the anterior corneal surface was also found to be positively correlated with vertical coma, spherical aberration, and tHOAs in Group M before SMILE (R² = 0.298, P < 0.001; R² = 0.138, P = 0.02; R² = 0.103, P = 0.046, respectively). In contrast, there was moderate positive correlation with spherical aberration in Group H (R² = 0.172, P = 0.032). In Group H, tHOAs had significantly positive correlation with the optical zone at 12 months postoperatively (R² = 0.339, P = 0.001). Furthermore, ocular HOAs were not correlated with the RA and HOI of the anterior/posterior corneal surface, refractive data, ablation depth, and cap thickness by linear regression analysis.

In this retrospective study, Fourier harmonic analysis was used to evaluate the associations between the ocular HOAs and Fourier indices, refraction, and surgical parameters after SMILE. Fourier analysis is a useful method to evaluate the optical information of video-keratographic data and to investigate the relationship between postoperative optical quality and visual function in refractive surgery.[15] The data of SC, RA, asymmetry, and HOI were shown by the Fourier analysis on the corneal topography. Asymmetry is a non-spherocylindrical corneal power component, representing the irregular corneal astigmatism, a tilt or decentration of the cornea noted on the videokeratoscope.[16] As described in previous studies, the anterior corneal asymmetry increased after SMILE,[9, 17] PRK,[12, 18] and LASIK[10, 19] in patients with myopia. In the current study, SC and RA decreased significantly, while the asymmetry component increased approximately two-fold after the surgery, based on the Fourier analysis of the anterior corneal surface after SMILE in both groups. These findings resonated partly with those of Sideroudi et al. who published the results of the corneal irregular astigmatism and curvature changes after SMILE in a three-year follow-up and concluded that the asymmetry and HOI of the anterior corneal surface increased despite the compensatory effect of the posterior corneal surface.[9] However, the relationships between the ocular wavefront aberration and Fourier indices were not investigated in their study.

It was well known that HOAs increased after SMILE, which might affect the visual quality.[20] Aruma et al. reported an increase in tHOAs, coma, spherical aberration, and vertical coma for patients with moderate myopia one year after SMILE.[21] Han et al. investigated 4-year wavefront aberrations for moderate-to-high myopia after SMILE and found HOAs, coma, and spherical aberration increased postoperatively.[22] In line with previous reports, vertical coma, horizontal coma, spherical aberration, and tHOAs after SMILE were significantly higher than the preoperative values at the one-year follow-up in the present study. Furthermore, Jin et al. compared the HOAs for high myopia and mild-to-moderate myopic patients before SMILE, 1 and 3 months postoperatively. Their results showed that the increase in vertical coma and spherical aberration was higher in the high myopia group than in the mild-to-moderate myopia group.[23] In our study, we found that the increase in the vertical coma was higher in Group H than in Group M at 3 and 6 months postoperatively.

Due to the absence of eye-tracking during the procedure of SMILE, the alignment of the refractive lenticule created by the femtosecond laser relied mostly on the corporation of the patient, which could increase the risk of decentered ablation. Decentration during refractive surgery may result in undesirable side effects, such as suboptimal aberrometry outcomes, halos, glare, monocular diplopia, and a reduction in visual acuity.[24] Coma can induce HOAs predominantly, which is a well-known phenomenon in SMILE,[25] related to treatment decentration.[26] Former investigators have already found the association between the total decentered displacement and induced coma, spherical aberration, and tHOAs, which were significant after SMILE.[27–29] Furthermore, Shao et al. evaluated the effect of angle kappa in SMILE and found that adjusting angle kappa during the SMILE procedure is associated with fewer HOAs.[6] Interestingly, previous studies did not reveal any relevant coherence between SMILE-induced HOAs with the topography data assessed by Fourier harmonic analysis. In this study, we conducted a series of correlation analyses between the Fourier indices and wavefront aberrations in each group. There were significant positive relationships between the corneal asymmetry of the anterior corneal surface and vertical coma, spherical aberration, and tHOAs among the HOAs during one-year follow-up after SMILE. Considering the aforementioned increments in ocular HOAs and asymmetry, we assumed that lenticule removal and corneal wound healing might lead to the asymmetry of the anterior corneal surface after surgery, which could induce an increase in ocular HOAs.

Corneal refractive surgery reshapes the anterior cornea to modify its refractive power. Previous studies indicated that the increase in the corneal asymmetry after LASIK significantly correlated with ablation depth.[10] While corneal asymmetry was significantly higher in Group H than in Group M after SMILE in this study. Since there was more stroma loss in high myopic eyes, it was reasonable to assume that the amount of the ablated or extracted stromal tissue might affect the asymmetry of the corneal surface.[30] We also found a correlation between corneal asymmetry and the amount of ablation depth. Fourier indices of the posterior corneal surface did not change significantly after surgery in both groups. The increment of asymmetry of the anterior corneal surface might be interpreted as a result of the corneal remodeling due to a biomechanical response to the geometrical mismatch between the undersurface of the cap and the stromal bed after lenticule removal.

In the current study, a significant decrease in the SC and RA of the anterior corneal surface and SC of the posterior corneal surface were observed in both groups after SMILE. In consistent with previous studies, SC and RA values were proportional to the keratometric spherical and astigmatic power.[31] However, Sideroudi et al. reported that the change in SC of the posterior corneal surface was obvious only in the high myopia group.[9] Our results showed a positive correlation between SC of the posterior corneal surface and HOAs to some extent, but the results were inconsistent with different postoperative times for the two groups. Since the lenticule created by the femtosecond laser was removed from the corneal stroma through a small incision, the refractive component was designed to be the posterior surface of the lenticule.[32] We speculated that these might lead to posterior stromal remodeling behavior. Further study with longer follow-up will be needed to elucidate the exact influence of the Fourier indices on visual performance, such as glare visual acuity, contrast sensitivity, and modulation transfer function. Other factors could influence perceived ocular HOAs, such as tear film quality, pupil size, and interindividual neuroadaptation to surgically induced HOAs. More research seems warranted to elucidate these complex interactions.

In conclusion, we evaluated the changes in corneal topography using Fourier harmonic analysis, ocular HOAs, and refractive power for moderate-to-high myopia during the one-year follow-up after SMILE. We explored the relationships between keratometric data by Fourier analysis and HOAs, which found a positive correlation between the asymmetry of the anterior corneal surfaces and vertical coma, spherical aberration, and tHOAs postoperatively. The visual quality after SMILE was associated with the asymmetry of the anterior corneal surface. The association could be attributed to corneal remodeling behavior, although the mechanisms were not fully understood. Nevertheless, the limitations of this study were the retrospective nature, the relatively small sample size and the group of low myopia was not included in this study. Future studies are needed to validate these associations for long-term outcomes after SMILE.

SMILE

Small-incision lenticule extraction

HOAs

Higher order aberrations

LASIK

Laser in situ keratomileuses

PRK

Photorefractive keratectomy

Penetrating keratoplasty

UDVA

Uncorrected distance visual acuity

CDVA

Corrected distance visual acuity

Spherical equivalent

Spherical component

Regular astigmatism

HOI

Higher-order irregularity.

Conflicts of interest:

The authors have declared that there were no competing interests to declare.

Ethics approval and consent to participate

This study followed the tenets of the Declaration of Helsinki and was approved by the Ethics Committee of the Shanghai Tenth People’s Hospital. All participants signed informed consents.

Consent for publication

Not applicable.

Availability of data and materials

Not applicable.

Competing interests

The authors have declared that there were no competing interests to declare.

Funding

This work was supported by Project of Shanghai Science and Technology (20ZR1443600 and No.17411950207), Multi-Center Clinical Research Project of Shanghai Shenkang Hospital Development Center (SHDC2020CR1043B-009), and Clinical Science and Technology Innovation Project of Shanghai ShenKang Hospital Development Center (SHDC12018103).

Authors' contributions

YHS, LNS and LL collected the data. MLD conducted the analysis and interpretation of patient data, and authored the manuscript. LL and ML participated in manuscript revisions. JZ contributed to the manuscript's design and review. All authors read and approved the final manuscript.

Acknowledgements

We thank all participants in this study.

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No competing interests reported.

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Corneal Asymmetry and Ocular Higher-Order Aberrations after Small Incision Lenticule Extraction for Moderate-to-High Myopia in One Year

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Abstract

Background

Methods

Results

Conclusions

Figures

Introduction

Patients and Methods

Patients

SMILE procedure

Examination

Statistical analysis

Results

Visual acuity and refraction

Wavefront aberrations

Fourier analysis

Linear regression analysis

Discussion

Conclusions

Abbreviations

Declarations

References

Additional Declarations

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