Early visual function outcomes of topography-guided FS-LASIK and SMILE in treatment of myopia and myopic astigmatism

Comparing femtosecond LASIK and small-incision lenticule extraction (SMILE)

PURPOSE OF REVIEW

This review compares two refractive surgery modalities, femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and small-incision lenticule extraction (SMILE), focusing on their efficacy, safety, postoperative recovery, and patient-reported outcomes. The aim is to provide an updated review of recent findings and identify areas for additional research to further optimize surgical outcomes and patient selection.

RECENT FINDINGS

FS-LASIK and SMILE show excellent, comparable visual outcomes for the correction of myopia and astigmatism. SMILE may have a lower risk of dry eye and has no flap-related complications, while FS-LASIK provides quicker visual recovery. SMILE may offer superior long-term visual outcomes, particularly for high myopia. However, customized FS-LASIK (wavefront- and topography-guided) outperform SMILE in some visual metrics, including uncorrected visual acuity and reduction in higher-order aberrations.

SUMMARY

FS-LASIK remains the gold standard refractive procedure due to its rapid recovery and predictable results, but SMILE offers advantages in preserving corneal biomechanical stability and potentially minimizing dry eye symptoms. SMILE may also offer improved long-term stability for patients at risk of myopic regression. However, a growing body of evidence suggests that wavefront- and topography-guided LASIK yield superior visual outcomes compared to SMILE. Additional long-term comparative studies are needed for different refractive treatment requirements.

Corneal Epithelial Remodeling Following Cylinder Correction With SMILE or FS-LASIK: A Contralateral Comparative Study

PURPOSE

To compare the corneal epithelial remodeling in eyes with high astigmatism that had small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK).

METHODS

Seventy-four patients with myopic astigmatism of greater than -2.00 diopters (D) and little binocular difference in spherical equivalent were included in this contralateral comparative study. All patients received SMILE in one eye and FS-LASIK in the other eye randomly. The corneal epithelial remodeling pattern was mapped using the latest RTVue spectral-domain optical coherence tomographer (Optovue) by region.

RESULTS

Satisfactory refractive correction was achieved in all enrolled eyes with either SMILE or FS-LASIK. The corneal epithelium gradually thickened following surgical cylinder correction, distributing mainly along the flat medium. The corneal epithelium proliferation is milder centrally but more pronounced in the mid-peripheral area after SMILE, compared with FS-LASIK. The flat-steep difference in corneal epithelial thickness (CET) is evident in the mid-peripheral and peripheral areas, which is more obvious in SMILE. Residual cylinder was positively correlated with CET in eyes that had FS-LASIK, but not SMILE. More importantly, these epithelial changes were positively correlated with the ablation depth and higher order aberrations following surgical refractive correction.

CONCLUSIONS

The postoperative CET map varied between SMILE and FS-LASIK. In eyes with high astigmatism, SMILE surgery is followed by milder and more stable corneal epithelial thickening. Moreover, the corneal epithelium is sensitive to stromal ablation and corneal remodeling is crucial to the postoperative visual quality. This study rigorously distinguished the CET difference between SMILE and FS-LASIK in astigmatic eyes and shed light on subsequent research. [J Refract Surg. 2024;40(10);e728-e741.].

Three-Month Comprehensive Outcomes of Topography-Guided LASIK Versus Keratorefractive Lenticule Extraction (KLEx): A Prospective Contralateral Study

INTRODUCTION

The aim of this study was to compare outcomes of topography-guided laser-assisted in situ keratomileusis (TG-LASIK) and small incision lenticule extraction (SMILE®) for correcting myopia and myopic astigmatism.

METHODS

In this prospective, randomized contralateral study, 34 patients (68 eyes) received TG-LASIK in one eye, and SMILE in their fellow eye. Efficacy, safety, predictability, higher-order aberrations, corneal tomography, biomechanics, and patient-reported outcomes (PROs) were assessed preoperatively and up to 3 months postoperatively.

RESULTS

Both platforms showed comparable efficacy at 3 months (TG-LASIK 1.08 ± 0.19; SMILE 0.98 ± 0.17, p = 0.055). However, TG-LASIK demonstrated quicker visual recovery, with 63% and 89% achieving uncorrected distance visual acuity (UDVA) of 20/16 or better at 1 day and 1 week, respectively, compared to SMILE (34% and 63%; p < 0.05). Safety index at 3 months did not significantly differ between TG-LASIK and SMILE (p = 0.223). TG-LASIK and SMILE had 44% and 56% of eyes within 0.13 D of spherical equivalent (SEQ) target, respectively. SMILE induced more total higher-order aberrations (HOAs), vertical coma, and oblique trefoil than TG-LASIK at 3 months (p < 0.05). Both platforms showed similar increases in epithelial remodeling, but SMILE induced thicker epithelium than TG-LASIK at the 7.0-mm nasal zonal area. No significant differences were found in corneal hysteresis (CH) or corneal resistance factor (CRF) at 3 months (p > 0.05). Reported symptoms of glare, halos, rings, starbursts, or dry eye did not significantly differ between groups at 3 months (p > 0.05). Overall, 59% of patients preferred their TG-LASIK treated eye at 1 month, but 65% of patients had no specific eye preference at 3 months.

CONCLUSION

TG-LASIK and SMILE demonstrate excellent and comparable efficacy, safety, and predictability at 3 months, but TG-LASIK offers faster postoperative visual recovery at 1 day and 1 week. TG-LASIK induces fewer HOAs than SMILE, but both procedures affect corneal biomechanics similarly.

TRIAL REGISTRATION

ClincialTrials.gov identifier, NCT05611294.

Differences in ocular high order aberrations before and after small incision lenticule extraction for correction of myopia: a systematic review and meta-analysis

Objective

To examine the causes and factors that lead to high order aberration (HOA) during the treatment of myopia using small incision lenticule extraction (SMILE), as well as the differences between SMILE and other corneal refractive surgeries through a systematic review and meta-analysis.

Methods

A systematic search was conducted from January 2015 to February 2023 in Pubmed, Embase, Web of Science, and Google Scholar databases to gather relevant studies on SMILE and HOA. Studies meeting specific criteria were chosen, and clinical data was retrieved for analysis.

Results

This meta-analysis resulted in the inclusion of 19 studies involving 1,503 eyes. Pooled results showed significant induction of total HOA (tHOA, d = -0.21, p < 0.001), spherical aberration (SA, d = -0.11, p < 0.001) and coma aberration (CA, d = -0.18, p < 0.001) after SMILE compared to pre-SMILE, while no significant change in trefoil aberration (TA) was observed (d = -0.00, p = 0.91). There was a significantly lower induction of tHOA after SMILE compared to femtosecond laser-assisted in situ keratomileusis (FS-LASIK, d = 0.04, p < 0.001), and no significant difference was observed compared to wavefront aberration-guided (WFG) refractive surgery (d = 0.00, p = 0.75). There was also a significant association between different levels of myopia and astigmatism, duration of follow-up, lenticule thickness, and preoperative central corneal thickness (CCT) on the induction of tHOA after SMILE (p < 0.05), while the higher preoperative myopia group (sphere > -5D), lower preoperative astigmatism group (cylinder ≤ -1D), larger lenticule thickness group (lenticule thickness > 100 μm), shorter follow-up group (follow-up 1 month postoperatively) and the thicker CCT group (CCT > 550 μm) brought a significant induction of tHOA compared to the opposite comparison group (p < 0.001).

Conclusion

While SMILE can induce HOA significantly, it induces less HOA than FS-LASIK. Postoperative HOA following SMILE can be affected by factors such as myopia, astigmatism, lenticule thickness, CCT, and duration of follow-up. Future research should continue to explore techniques to decrease the induction of HOA by using this methodology.

Systematic review registration

https://www.crd.york.ac.uk/prospero/.

Topographic and surgical risk factors for high postoperative residual astigmatism after small incision lenticule extraction in patients with different degrees of myopia: a retrospective cohort study

BACKGROUND

To evaluate the possible topographic and surgical risk factors for high postoperative residual astigmatism in patients who undergo small-incision lenticule extraction (SMILE) surgery and have different myopia degrees.

METHODS

A retrospective cohort study was conducted, and patients who underwent SMILE surgery were enrolled. A total of 80 and 150 eyes from 40 to 75 individuals, respectively, were selected as the low myopia and high myopia groups. The demographic data, visual acuity, refraction, topographic parameters and surgical settings were recorded. Multiple linear regression with interaction tests were performed to survey the risk factors for high postoperative residual astigmatism in each group.

RESULTS

Five (6.25%) and 9 (6.00%) eyes presented with high postoperative residual astigmatism in the low myopia and high myopia groups, respectively, but these differences were not significant (P = 0.569). A steep corneal curvature was correlated with a greater risk of high postoperative residual astigmatism in the low myopia group (P = 0.015), while a higher degree of cycloplegic cylinder power, steeper corneal curvature, greater topographic cylinder power, smaller optic zone and longer incision length were associated with a high rate of postoperative residual astigmatism in the high myopia group (all P < 0.05). In addition, the interaction effects of cycloplegic and topographic cylinder power and longer incision length on the incidence of high postoperative residual astigmatism development were more evident in the high myopia group than in the low myopia group (all P < 0.05).

CONCLUSIONS

A steep corneal curvature correlates with a high risk of high postoperative residual astigmatism after SMILE surgery, and a higher degree of cycloplegic and topographic cylinder and longer incision are associated with high postoperative residual astigmatism in individuals with high myopia.

Intensive topical steroid regimen for enhanced very early recovery after small incision lenticule extraction

OBJECTIVE

This study aims to investigate the topical steroid regimen after small incision lenticule extraction (SMILE) for its effect on very early restoration of visual quality.

METHODS

A total of 180 patients (360 eyes) who underwent SMILE were enrolled. These patients were randomly assigned to three groups, with 60 patients in each group. The only difference among these three groups was the administration of 0.1% fluorometholone (FML) eye drops within two hours after SMILE: no FML in group A, 0.1% FML once every hour in group B and 0.1% FML once every half hour in group C. The corrected distance visual acuity (CDVA), objective scattering index (OSI), modulation transfer function (MTF) cut-off, Strehl ratio (SR) and incidence of subjective symptoms were evaluated preoperatively, at 2, 4 and 24 h and one week after SMILE.

RESULTS

The CDVA, MTF cut-off and SR values were significantly higher in group C, when compared to the other two groups, at 2 and 4 h after SMILE (p < 0.05). Furthermore, the OSI and incidence of subjective symptoms were significantly lower in group C, when compared to the other two groups, at 2 and 4 h after SMILE (p < 0.05). However, no significant differences in CDVA, MTF cut-off, SR, OSI and the incidence of subjective symptoms were detected among the three groups at 24 h and one week after SMILE (p > 0.05).

CONCLUSION

The administration of 0.1% FML eye drops every half hour within two hours after SMILE accelerates the restoration of visual and optical quality, and reduces the incidence of subjective symptoms during the very early phase after surgery.

Prediction of SMILE surgical cutting formula based on back propagation neural network

AIM

To predict cutting formula of small incision lenticule extraction (SMILE) surgery and assist clinicians in identifying candidates by deep learning of back propagation (BP) neural network.

METHODS

A prediction program was developed by a BP neural network. There were 13 188 pieces of data selected as training validation. Another 840 eye samples from 425 patients were recruited for reverse verification of training results. Precision of prediction by BP neural network and lenticule thickness error between machine learning and the actual lenticule thickness in the patient data were measured.

RESULTS

After training 2313 epochs, the predictive SMILE cutting formula BP neural network models performed best. The values of mean squared error and gradient are 0.248 and 4.23, respectively. The scatterplot with linear regression analysis showed that the regression coefficient in all samples is 0.99994. The final error accuracy of the BP neural network is -0.003791±0.4221102 µm.

CONCLUSION

With the help of the BP neural network, the program can calculate the lenticule thickness and residual stromal thickness of SMILE surgery accurately. Combined with corneal parameters and refraction of patients, the program can intelligently and conveniently integrate medical information to identify candidates for SMILE surgery.

Topography-guided excimer laser ablation

PURPOSE OF REVIEW

Currently, the most commonly performed corneal refractive surgery is laser-assisted in-situ keratomileusis (LASIK). Customized forms of LASIK have been developed, which have allowed for improved outcomes and the enhanced correction of higher order aberrations (HOAs). This review discusses one form of custom LASIK, topography-guided LASIK, including factors involved in preoperative planning, and advantages and disadvantages compared with other forms of keratorefractive surgery.

RECENT FINDINGS

Various treatment-planning approaches addressing discrepancies between the refractive and topographic astigmatic magnitude and axis have been used successfully, although there is debate regarding a superior method in the literature.

SUMMARY

There are many forms of custom LASIK, which provide excellent outcomes. Topography-guided LASIK may be of particular use in highly aberrated corneas and may also provide outstanding outcomes in healthy eyes given its emphasis on treating the primary refractive surface of the eye.