Comparison of Postoperative Corneal Higher-Order Aberrations, Asphericity, Densitometry, and Optical Quality Between SMILE Pro and LASIK: A Retrospective Cohort Study

Abstract

Purpose

To compare postoperative changes in corneal higher-order aberrations (HOAs), densitometry, and optical quality following SMILE Pro and laser in situ keratomileusis (LASIK), and to investigate the relationship between corneal densitometry and postoperative optical quality.

Patients and Methods

This retrospective matched cohort study included 60 eyes of 30 patients who underwent SMILE Pro and 60 eyes of 30 age-, sex-, and preoperative spherical equivalent-matched patients who underwent LASIK for myopia at Hanamizuki Eye Clinic between July 2025 and March 2026. Anterior, posterior, and real corneal HOAs, spherical aberration (SA), coma, anterior corneal Q value, and central (0–4 mm) corneal densitometry were evaluated using anterior segment optical coherence tomography (CASIA2). Optical quality was assessed using the modulation transfer function (MTF) Area Ratio (Total and HO) obtained with the OPD-Scan III. Longitudinal comparisons were analyzed using linear mixed-effects models, and correlations were evaluated using Spearman’s rank correlation coefficient.

Results

Compared with LASIK, the SMILE Pro group showed significantly lower posterior corneal coma at 1 week, lower anterior and real SA at 1 month, and lower anterior and real SA as well as real corneal coma at 3 months (all P<0.05). Q values were significantly lower at 1 and 3 months. Corneal densitometry was significantly higher in the SMILE Pro group at 1 week, 1 month, and 3 months (all P<0.05), whereas the 3-month MTF Area Ratio Total was significantly lower (P=0.004). Within the SMILE Pro group, corneal densitometry at 1 week, 1 month, and 3 months was significantly negatively correlated with the 3-month MTF Area Ratio HO (all P<0.05), whereas no significant correlations were observed in the LASIK group.

Conclusion

Compared with LASIK, SMILE Pro was associated with fewer postoperative corneal HOAs and better preservation of corneal asphericity. Although higher-order optical quality was comparable between the two procedures, postoperative corneal densitometry was associated with higher-order optical quality only after SMILE Pro. These findings suggest that anterior segment OCT-derived corneal densitometry may provide additional noninvasive information on postoperative stromal interface healing and its relationship with optical quality following SMILE Pro.

Plain Language Summary

Why was this study done?

SMILE Pro is a new laser vision correction procedure that has been developed to improve the accuracy and safety of conventional SMILE surgery. Although previous studies have shown that SMILE Pro provides excellent visual outcomes, little is known about how postoperative corneal healing may be related to optical quality. We therefore compared SMILE Pro with LASIK, a widely used refractive procedure, focusing on corneal optical properties and postoperative healing.

What did the researchers do and find?

We retrospectively compared 60 eyes that underwent SMILE Pro with 60 matched eyes that underwent LASIK. Corneal higher-order aberrations, corneal shape, corneal densitometry (an objective measure of corneal light scatter), and optical quality were evaluated for up to 3 months after surgery. SMILE Pro was associated with fewer postoperative corneal optical aberrations and better preservation of the natural corneal shape than LASIK. However, corneal densitometry remained higher after SMILE Pro, which may reflect ongoing stromal interface healing. In addition, only the SMILE Pro group showed a significant association between corneal densitometry and postoperative optical quality, suggesting a possible relationship between subtle wound-healing responses and optical quality after surgery.

What do these results mean?

These findings suggest that postoperative optical quality after SMILE Pro may be associated not only with corneal aberrations but also with stromal interface healing. Corneal densitometry may provide a useful, noninvasive measure for monitoring postoperative corneal changes and may offer additional clinical information beyond conventional visual acuity and refractive measurements. Further prospective studies with larger sample sizes and longer follow-up are needed to confirm these findings.

Introduction

Corneal refractive surgery has undergone remarkable advances over the past three decades and has become an established treatment for myopia and myopic astigmatism. Since its clinical introduction in the 1990s, laser in situ keratomileusis (LASIK) has become the most widely performed corneal refractive procedure because of its excellent safety, efficacy, and predictability.¹˒² However, LASIK requires creation of a corneal flap, which may be associated with flap-related complications, postoperative dry eye caused by transection of the corneal subbasal nerve plexus, and reduced corneal biomechanical strength.³

To overcome these limitations, Refractive Lenticule Extraction (ReLEx) was developed and subsequently evolved into Small Incision Lenticule Extraction (SMILE; VisuMax 500, Carl Zeiss Meditec), a flap-free procedure in which an intrastromal lenticule is removed through a small corneal incision.⁴˒⁵ By preserving Bowman’s layer and the anterior corneal stroma, SMILE has been shown to reduce postoperative dry eye and better preserve corneal biomechanical properties than LASIK.^6–9 Furthermore, a recent meta-analysis of randomized clinical trials showed that SMILE was associated with lower postoperative spherical aberration while providing refractive and visual outcomes generally comparable to those of LASIK.¹⁰

More recently, the second-generation SMILE platform, SMILE Pro (VisuMax 800), has been introduced into clinical practice. It incorporates a 2-MHz femtosecond laser that reduces laser treatment time from approximately 25–30 seconds to 8–10 seconds. In addition, CentraLign and OcuLign technologies improve centration and cyclotorsion compensation, potentially enhancing treatment accuracy and postoperative optical performance.^11,12

Visual quality after corneal refractive surgery depends not only on refractive accuracy but also on postoperative corneal optical properties. Corneal higher-order aberrations (HOAs), particularly SA and coma, together with the anterior corneal Q value, are established indicators of postoperative optical quality.¹³ Recent advances in anterior segment optical coherence tomography (AS-OCT) have enabled quantitative assessment of corneal densitometry, which reflects subtle intrastromal light scattering and may serve as a noninvasive indicator of postoperative wound healing and stromal interface remodeling.^14,15 Optical quality can also be evaluated using the modulation transfer function (MTF) Area Ratio, which reflects the optical performance of the entire ocular system.

Although postoperative visual and refractive outcomes have been extensively investigated after conventional SMILE and LASIK, information regarding corneal densitometry and its relationship with optical quality after SMILE Pro remains limited. In particular, whether postoperative stromal interface healing influences optical quality following SMILE Pro has not been fully elucidated.

Therefore, this study aimed to compare postoperative corneal higher-order aberrations, asphericity, densitometry, and optical quality between SMILE Pro and LASIK, and to investigate the relationship between postoperative corneal densitometry and optical quality.

Patients and Methods

Study Design and Patients

This retrospective matched cohort study was conducted at Hanamizuki Eye Clinic, Ehime, Japan. Medical records of patients who underwent corneal refractive surgery for myopia or myopic astigmatism between July 2025 and March 2026 were retrospectively reviewed.

Thirty patients (60 eyes) who underwent SMILE Pro and 30 age-, sex-, and preoperative spherical equivalent (SE)-matched patients (60 eyes) who underwent LASIK were included. Matching was performed to minimize baseline differences between the two groups. Patients with keratoconus, corneal ectasia, previous corneal surgery, ocular trauma, intraoperative complications, or postoperative complications were excluded.

All patients underwent a comprehensive preoperative ophthalmic examination, including manifest refraction, slit-lamp biomicroscopy, fundus examination, and optical coherence tomography for macular evaluation. Eyes with ocular conditions that could affect visual or optical quality, including clinically significant lens opacity, macular pathology, myopic macular degeneration, or other retinal diseases, were excluded.

This study adhered to the tenets of the Declaration of Helsinki and was approved by the Institutional Review Board of Ehime University School of Medicine (No. 2607001). Because of the retrospective study design, the requirement for written informed consent was waived, and all patients were provided with an opportunity to opt out through public disclosure of the study information.

Surgical Procedures

SMILE Pro

SMILE Pro was performed using the VISUMAX 800 femtosecond laser system (version 1.1; Carl Zeiss Meditec, Jena, Germany). Standard surgical settings included a laser frequency of 2 MHz, cap thickness of 100–120 μm, cap diameter of 7.5 mm, optical zone of 6.2–6.5 mm, and a superior incision of 2–3 mm. CentraLign and OcuLign technologies were applied in all cases to facilitate centration and cyclotorsion compensation.

LASIK

LASIK was performed using the IntraLase FS femtosecond laser (Johnson and Johnson Vision, USA) to create a 100-μm corneal flap, followed by wavefront-guided excimer laser ablation using the VISX STAR S4 IR excimer laser system (version 5.32; Johnson and Johnson Vision).

Outcome Measurements

All examinations were performed preoperatively and at 1 week, 1 month, and 3 months postoperatively.

Visual and Refractive Outcomes

Refractive characteristics, including sphere, cylinder, and spherical equivalent, as well as uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA), were recorded. Endothelial cell density was also recorded as a baseline ocular characteristic. At our clinic, manifest refractive astigmatism of ≥0.25 D in absolute magnitude was considered eligible for astigmatic correction. Astigmatism was classified according to the minus-cylinder axis as with-the-rule (WTR; 0°–30° or 150°–180°), against-the-rule (ATR; 60°–120°), or oblique (31°–59° or 121°–149°).

Corneal Higher-Order Aberrations

Anterior segment optical coherence tomography (version 50.7D.05, CASIA2; Tomey, Japan) was used to measure anterior corneal, posterior corneal, and real corneal wavefront aberrations. The following parameters were analyzed:

• Higher-order aberrations (HOAs)

• Spherical aberration (SA)

• Coma aberration (coma)

Corneal Asphericity

Anterior corneal Q value was measured using CASIA2 as an indicator of postoperative corneal asphericity.

Corneal Densitometry

Corneal densitometry within the central 0–4-mm diameter zone was measured using the built-in densitometry analysis software of the CASIA2.

Optical Quality

Optical quality was evaluated using the OPD-Scan III (version 1.37.1, NIDEK, Japan). The modulation transfer function (MTF) describes the ability of the optical system to preserve image contrast from the object to the retinal image, with higher values indicating better optical performance. The MTF Area Ratio, derived from the MTF curve, was analyzed for both the Total (overall optical system) and HO (higher-order aberrations) components.

Statistical Analysis

All statistical analyses were performed using JMP version 19 (SAS Institute Inc., Cary, NC, USA). Because this was a retrospective exploratory study based on eligible cases available during the predefined study period, an a priori sample size calculation was not performed. A sensitivity analysis based on the available sample size of 60 eyes per group indicated that, assuming a two-sided α level of 0.05 and 80% power, the study could detect a standardized between-group effect size of approximately 0.52 (Cohen’s d) under an independent-observation assumption. Because both eyes of individual patients were included, this sensitivity analysis should be interpreted as an approximate measure of statistical sensitivity rather than an exact power estimate for the primary analysis.

Longitudinal comparisons were performed using linear mixed-effects models to account for within-subject inter-eye correlation and repeated measurements. Surgical procedure (SMILE Pro or LASIK), postoperative time point (1 week, 1 month, and 3 months), and the interaction between procedure and time were treated as fixed effects, whereas individual patients were treated as random effects. Changes in SE, UDVA, HOAs, SA, coma, Q value, corneal densitometry, and MTF Area Ratio were compared between groups. Residual cylinder at 3 months was also compared between the two groups.

Associations between corneal densitometry and MTF Area Ratio were evaluated using Spearman’s rank correlation coefficient. A two-sided P value <0.05 was considered statistically significant.

Results

Visual and Refractive Outcomes

Baseline demographic and refractive characteristics were comparable between the SMILE Pro and LASIK groups (Table 1). Residual cylinder at 3 months also did not differ significantly between the groups (−0.35 ± 0.32 D vs −0.31 ± 0.28 D, respectively; P = 0.642). Postoperative SE and UDVA did not differ significantly between the groups at 1 week, 1 month, or 3 months (Table 2).

Table 1.

Baseline Characteristics of the SMILE Pro and LASIK Groups

Characteristic	SMILE Pro	LASIK	P value
Age, years	30.0±6.6	31.9±6.4	0.256
Patients/eyes, n	30/60	30/60	–
Sex, male/female, n	14/16	15/15	1.000
Sphere, D	−4.11±1.28	−4.28±1.52	0.782
Cylinder, D	−0.81±0.65	−0.86±0.72	0.682
SE, D	−4.52±1.05	−4.71±1.24	0.512
Myopic astigmatism, n (%)	56 (93.3%)	55 (91.7%)	1.000
Astigmatism type, n (%)			0.825
WTR	41 (73.2%)	43 (78.2%)
ATR	12 (21.4%)	10 (18.2%)
Oblique	3 (5.4%)	2 (3.6%)
ECD, cells/mm2	2798±268.2	2816±247.2	0.762
UDVA, LogMAR	1.16±0.28	1.18±0.48	0.667

Notes: Data are presented as mean ± standard deviation or n (%), as appropriate.

Abbreviations: SE, spherical equivalent; D, diopter; WTR, with-the-rule; ATR, against-the-rule; ECD, endothelial cell density; UDVA, uncorrected distance visual acuity; LogMAR, logarithm of the minimum angle of resolution.

Table 2.

Postoperative Visual and Refractive Outcomes in the SMILE Pro and LASIK Groups

Parameter	SMILE Pro	LASIK	P value
SE at 1 week, D	−0.12±0.46	0.06±0.23	0.389
SE at 1 month, D	−0.11±0.35	0.12±0.38	0.512
SE at 3 months, D	−0.09±0.32	0.11±0.52	0.436
UDVA at 1 week	−0.17±0.05	−0.18±0.07	0.677
UDVA at 1 month	−0.19±0.07	−0.21±0.05	0.739
UDVA at 3 months	−0.18±0.06	−0.17±0.09	0.588

Notes: Data are presented as mean ± standard deviation.

Abbreviations: SE, spherical equivalent; D, diopter; UDVA, uncorrected distance visual acuity. UDVA is presented in LogMAR (logarithm of the minimum angle of resolution) units.

Corneal Higher-Order Aberrations

Preoperatively, no significant differences were observed between the groups in anterior, posterior, or real corneal HOAs, SA, or coma (Table 3).

Table 3.

Corneal Higher-Order Aberrations in the SMILE Pro and LASIK Groups

	Preop		Postop 1W		Postop 1M		Postop 3M
	SMILE Pro	LASIK	SMILE Pro	LASIK	SMILE Pro	LASIK	SMILE Pro	LASIK
Ant HOAs	0.24±0.05	0.23±0.06	0.34±0.28	0.37±0.69	0.30±0.08	0.28±0.07	0.26±0.07	0.28±0.08
Post HOAs	0.05±0.01	0.05±0.01	0.08±0.07	0.09±0.19	0.06±0.02	0.06±0.01	0.06±0.02	0.06±0.01
Real HOAs	0.23±0.05	0.22±0.06	0.32±0.27	0.37±0.53	0.28±0.09	0.27±0.07	0.25±0.07	0.27±0.08
Ant SA	0.26±0.14	0.30±0.10	0.54±0.37	0.62±0.29	0.53±0.24*	0.63±0.18	0.51±0.21*	0.65±0.20
Post SA	−0.12±0.03	−0.11±0.04	−0.12±0.03	−0.11±0.02	−0.11±0.07	−0.11±0.02	−0.10±0.08	−0.11±0.02
Real SA	0.24±0.13	0.27±0.10	0.51±0.36	0.59±0.28	0.50±0.24*	0.61±0.16	0.48±0.20*	0.64±0.18
Ant coma	0.09±0.05	0.10±0.06	0.16±0.11	0.23±0.41	0.15±0.08	0.15±0.09	0.14±0.08	0.17±0.08
Post coma	0.01±0.01	0.01±0.01	0.01±0.01*	0.02±0.02	0.01±0.01	0.02±0.01	0.01±0.01	0.02±0.01
Real coma	0.08±0.05	0.09±0.06	0.16±0.10	0.23±0.39	0.15±0.08	0.16±0.08	0.13±0.08*	0.18±0.08

Notes: Asterisks indicate values significantly lower in the SMILE Pro group than in the LASIK group (P<0.05).

Abbreviations: Ant, anterior cornea; Post, posterior cornea; HOAs, higher-order aberrations; SA, spherical aberration; coma, coma aberration.

At 1 week postoperatively, posterior corneal coma was significantly lower in the SMILE Pro group than in the LASIK group (P=0.026). At 1 month, anterior and real corneal SA were significantly lower in the SMILE Pro group (P=0.031 and P=0.015, respectively). At 3 months, anterior and real corneal SA remained significantly lower in the SMILE Pro group (P=0.003 and P<0.001, respectively). In addition, real corneal coma was significantly lower in the SMILE Pro group than in the LASIK group (P=0.022).

Although HOAs tended to be lower in the SMILE Pro group throughout the follow-up period, no significant differences were observed in the other HOA parameters.

Corneal Asphericity

No significant difference in the anterior corneal Q value was observed between the groups preoperatively.

At 1 month and 3 months, the Q value was significantly lower in the SMILE Pro group than in the LASIK group (P=0.025 and P=0.003, respectively), consistent with better preservation of the physiological prolate corneal shape (Table 4).

Table 4.

Longitudinal Changes in Corneal Q Value and MTF Area Ratio

	Preop		Postop 1W		Postop 1M		Postop 3M
	SMILE Pro	LASIK	SMILE Pro	LASIK	SMILE Pro	LASIK	SMILE Pro	LASIK
Q value	−0.17±0.23	−0.19±0.25	0.56±0.98	0.89±1.23	0.51±0.75*	0.71±0.55	0.42±0.62*	0.75±0.57
MTF Total	13.3±16.3	12.4±10.7	35.9±12.9	38.2±13.9	38.5±15.0	41.1±15.9	37.9±14.3*	45.9±15.4
MTF HO	82.9±27.0	75.9±26.9	57.6±19.5	56.9±20.9	59.9±19.8	58.7±19.6	63.6±15.1	62.6±19.4

Notes: The MTF Area Ratio was calculated from the MTF curve, and both the Total and HO components were analyzed. Asterisks indicate statistically significant differences between the two groups (P<0.05).

Abbreviations: MTF, modulation transfer function; Total, total optical aberration component; HO, higher-order aberration component.

Corneal Densitometry

Preoperative corneal densitometry was comparable between the groups (P=0.765). Corneal densitometry decreased at 1 week in both groups compared with preoperative values. Corneal densitometry was significantly higher in the SMILE Pro group than in the LASIK group at 1 week (P=0.018), 1 month (P<0.001), and 3 months (P<0.001) (Figure 1).

Figure 1.

Longitudinal changes in corneal densitometry following SMILE Pro and LASIK. Corneal densitometry within the central 0–4-mm corneal zone was measured using CASIA2. Corneal densitometry was significantly higher in the SMILE Pro group than in the LASIK group at all postoperative time points. Data are presented as mean ± SD.

Optical Quality

No significant differences were observed in the preoperative MTF Area Ratio Total or HO between the groups.

At 3 months, the MTF Area Ratio Total was significantly lower in the SMILE Pro group than in the LASIK group (37.9 ± 14.3 vs 45.9 ± 15.4, P=0.004). In contrast, the MTF Area Ratio HO did not differ significantly between the groups at any postoperative time point (Table 4).

Association Between Corneal Densitometry and Higher-Order Optical Quality

In the SMILE Pro group, corneal densitometry measured at 1 week, 1 month, and 3 months showed significant negative correlations with the 3-month MTF Area Ratio HO (1 week: r=−0.356, P=0.005; 1 month: r=−0.349, P=0.006; 3 months: r=−0.313, P=0.015) (Figure 2).

Figure 2.

Correlation between corneal densitometry and 3-month MTF Area Ratio HO in the SMILE Pro group. Scatter plots showing the correlations between postoperative corneal densitometry and the 3-month MTF Area Ratio HO in the SMILE Pro group. Significant negative correlations were observed at all postoperative time points (Spearman’s rank correlation, P<0.05).

In contrast, no significant correlations were observed between corneal densitometry and the MTF Area Ratio HO in the LASIK group.

Discussion

The present study compared postoperative corneal HOAs, asphericity, densitometry, and optical quality between SMILE Pro and LASIK using AS-OCT and wavefront analysis. The principal findings were as follows. First, SMILE Pro was associated with significantly lower postoperative SA and coma than LASIK and with better preservation of physiological corneal asphericity. Second, corneal densitometry remained significantly higher after SMILE Pro despite comparable postoperative visual acuity and refractive outcomes. Third, although no significant intergroup difference was observed in the MTF Area Ratio HO, corneal densitometry showed significant negative associations with higher-order optical quality only in the SMILE Pro group. These findings suggest that postoperative stromal interface healing may be associated with optical quality following SMILE Pro.

Previous studies have suggested that SMILE induces fewer postoperative HOAs than LASIK. Yao et al reported in a meta-analysis of randomized clinical trials that SMILE was associated with lower postoperative SA while providing refractive and visual outcomes generally comparable to those of LASIK.¹⁰ The present findings for SMILE Pro are consistent with previous reports. Anterior and real corneal SA were significantly lower at both 1 and 3 months after SMILE Pro, whereas real corneal coma was also significantly lower at 3 months, consistent with better preservation of corneal optical geometry.

The postoperative optical characteristics observed after SMILE Pro may partly be related to technological advances incorporated into the procedure. The VISUMAX 800 platform employs a 2-MHz femtosecond laser, reducing laser delivery time from approximately 30 seconds to less than 10 seconds. Furthermore, CentraLign and OcuLign provide centration guidance and cyclotorsion compensation during surgery. Because coma is particularly sensitive to treatment decentration and rotational misalignment, the significantly lower postoperative real corneal coma observed after SMILE Pro may be partly related to the improved centration and cyclotorsion control provided by these technologies.^11,12

Anterior corneal Q values were also significantly lower after SMILE Pro than after LASIK, consistent with better preservation of the physiological prolate corneal shape. Since LASIK requires central stromal photoablation, postoperative corneal flattening frequently results in a more oblate corneal profile. Previous studies have shown that postoperative increases in Q value are closely associated with increased corneal spherical aberration.¹⁶ Unlike LASIK, SMILE Pro is a flapless procedure that avoids excimer laser photoablation of the anterior stromal surface, which may contribute to better preservation of postoperative corneal geometry. The concurrent differences in SA and Q value are consistent with better preservation of corneal geometry after SMILE Pro.

One of the most noteworthy findings of the present study was that corneal densitometry remained significantly higher after SMILE Pro despite lower postoperative HOAs. Corneal densitometry quantitatively reflects corneal light scatter and has been used to evaluate postoperative corneal changes and stromal wound-healing responses. In both groups, corneal densitometry decreased after surgery and remained below the preoperative level throughout the 3-month follow-up period. This overall decrease may partly reflect postoperative changes in corneal thickness, curvature, and optical path length. Nevertheless, corneal densitometry remained significantly higher after SMILE Pro than after LASIK throughout the postoperative follow-up period. Previous studies by Wei et al and Han et al similarly reported prolonged changes in corneal backscatter following SMILE, which may reflect stromal interface remodeling persisting for several months after surgery.^14,15 Our findings suggest that similar postoperative stromal remodeling may also occur following SMILE Pro.

Interestingly, the MTF Area Ratio Total was significantly lower after SMILE Pro at 3 months, whereas the MTF Area Ratio HO did not differ significantly between the two procedures. Although these findings may initially appear inconsistent with the lower corneal HOA values observed after SMILE Pro, postoperative optical quality is multifactorial and cannot be explained solely by corneal HOAs or densitometry. Although our data showed that residual cylinder at 3 months did not differ significantly between the groups, lower-order aberrations, including residual defocus and astigmatism, may still affect overall optical performance at the individual level. In addition, tear-film stability, intraocular light scatter, and neural adaptation may influence postoperative optical and visual quality. Therefore, differences in corneal aberrations alone do not necessarily translate into differences in overall optical quality.¹⁷ Future prospective studies are needed to further clarify the relative contributions of these factors to optical quality following SMILE Pro and LASIK.

More importantly, only the SMILE Pro group showed significant negative associations between corneal densitometry and the MTF Area Ratio HO throughout the postoperative period, whereas no such relationship was observed after LASIK. Although the MTF Area Ratio HO itself was comparable between the two groups, these findings suggest that postoperative optical quality following SMILE Pro may be associated with inter-individual differences in stromal interface healing. Microscopic wound-healing responses that are not apparent on conventional clinical examination may be associated with variations in higher-order optical performance following SMILE Pro. These findings suggest that corneal densitometry may provide a noninvasive quantitative measure of postoperative stromal interface changes.

Notably, postoperative visual acuity and refractive outcomes were comparable between the two procedures throughout the follow-up period. Therefore, the higher corneal densitometry observed after SMILE Pro should not necessarily be interpreted as clinically apparent corneal haze but may instead reflect subtle postoperative microstructural changes detectable by AS-OCT. From a clinical perspective, quantitative assessment of corneal densitometry may provide additional information regarding postoperative corneal healing beyond conventional visual and refractive evaluations.

A major strength of the present study is the comprehensive evaluation of corneal HOAs, corneal asphericity, corneal densitometry, and optical quality using both AS-OCT and wavefront analysis in matched cohorts undergoing SMILE Pro or LASIK. To our knowledge, this is the first study to identify a significant association between postoperative corneal densitometry and higher-order optical quality following SMILE Pro. These findings may provide new insights into the relationship between stromal interface healing and optical quality after this procedure.

This study has several limitations. First, postoperative follow-up was limited to 3 months, and longer-term postoperative changes remain to be clarified. Second, subjective visual quality, including contrast sensitivity, night vision, and patient-reported outcome measures, was not evaluated. Third, corneal densitometry was assessed only within the central 0–4-mm zone using a single AS-OCT platform; therefore, the reproducibility of these findings using other imaging devices or wider analysis areas remains to be investigated. Finally, because this was a retrospective and exploratory study, an a priori sample size calculation was not performed. Therefore, the findings should be interpreted as exploratory and require confirmation in adequately powered prospective studies.

Conclusion

SMILE Pro was associated with lower postoperative corneal spherical aberration and coma and better preservation of physiological corneal asphericity than LASIK during the 3-month follow-up. Corneal densitometry remained higher after SMILE Pro and was negatively associated with the MTF Area Ratio HO within the SMILE Pro group, suggesting that postoperative stromal interface changes might be related to optical performance. Given the retrospective and exploratory nature of the study, these findings should be interpreted cautiously and confirmed in larger prospective studies with longer follow-up.

Funding Statement

The authors received no financial support for this work.

Proprietary Interest

The authors have no proprietary interest in any materials or methods described within this article.

Abbreviations

AS-OCT, anterior segment optical coherence tomography; CDVA, corrected distance visual acuity; HOAs, higher-order aberrations; LASIK, laser in situ keratomileusis; MTF, modulation transfer function; Q value, corneal asphericity value; SA, spherical aberration; SE, spherical equivalent; SMILE, small incision lenticule extraction; UDVA, uncorrected distance visual acuity.

Data Sharing Statement

The datasets generated and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Ethics Approval and Informed Consent

The study adhered to the tenets of the Declaration of Helsinki and was approved by the Institutional Review Board of Ehime University School of Medicine (No. 2607001).

Because of the retrospective design, informed consent was waived. Instead, patients were provided with an opportunity to decline participation through an opt-out procedure.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest in this work.