Comparison of ocular higher-order aberrations after SMILE and Wavefront-guided Femtosecond LASIK for myopia

Evaluation of Higher-Order Aberrations After the Smooth Incision Lenticular Keratomileusis (SILKTM) Procedure Using the ELITATM Femtosecond Platform for Correction of Myopic and Astigmatic Refractive Errors

Purpose

To evaluate the changes of higher-order wavefront aberrations following the Smooth Incision Lenticular Keratomileusis (SILKTM) procedure for correction of myopic refractive errors with and without astigmatism, using the ELITATM Femtosecond Platform.

Methods

This prospective study included 24 eyes that underwent SILK procedure using one ELITA femtosecond laser system for the correction of myopic refractive errors with and without astigmatism. Preoperative and postoperative 1-day, 1-week, 1-month, 3-month, and 9-month eye exams were measured with a commercial wavefront aberrometer (iDESIGN ® Refractive Studio, Johnson & Johnson Surgical Vision, Inc). Wavefront aberrations up to the 6th order Zernike coefficients, including coma Z(3, -1) and Z(3, 1), spherical aberration Z(4, 1), and the wavefront error of all higher-order aberrations (HOAs RMS), were evaluated across a 6 mm pupil.

Results

The mean manifest refractive spherical equivalent changed from the preoperative refractions -3.82 ± 1.26 D (range -6.00 to -2.25 D) to the postoperative refractions -0.20 ± 0.15 D (range -0.50 to 0.00 D) at the 9-month follow-up. Compared to baseline preoperative HOAs, the mean postoperative HOAs were significantly increased at the 1-day follow-up. On average, at the 9-month postoperative assessment the vertical coma Z(3, -1) was -0.054 ±0.186 µm, horizontal coma Z(3, 1) was 0.016 ± 0.124 µm, spherical aberration Z(4, 0) was 0.046 ± 0.163 µm, and HOAs RMS was 0.363 ± 0.115 µm across a 6 mm pupil. There is no significant difference in the mean HOAs starting at 1-week follow-up for the horizontal coma (P = 0.346) and spherical aberration (P = 0.095).

Conclusions

The visual outcomes demonstrated that the SILK procedure for refractive lenticule extraction using ELITA femtosecond laser system is effective and predictable for the correction of myopic refractive errors with and without astigmatism. The ELITA femtosecond laser system induced minimal HOAs in surgical eyes following the SILK procedures. These results demonstrate fast corneal recovery starting at 1-week follow-up, and spherical aberration was not induced.

Femtosecond laser-assisted in situ keratomileusis versus small-incision lenticule extraction: current approach based on evidence

PURPOSE OF REVIEW

Laser keratorefractive surgery achieves excellent visual outcomes for refractive error correction. With femtosecond laser, small incision lenticule extraction (SMILE) is an increasingly viable alternative to laser-assisted in situ keratomileusis (LASIK). Comparative studies demonstrate similar efficacy and predictability between SMILE and LASIK, making it difficult for clinicians to choose which to use. This review thus compares femtosecond-LASIK (FS-LASK) and SMILE in various scenarios, to assist clinicians in deciding which refractive surgery procedure to recommend.

RECENT FINDINGS

SMILE may be superior for highly myopic eyes due to a smaller decrease in functional optical zone. SMILE further induces less spherical aberration and less overall higher order aberrations in mesopic conditions. SMIILE also has less postoperative dry eye, making it suitable those with preexisting dry eye. For low to moderate myopic astigmatism correction, FS-LASIK has less undercorrection compared to SMILE. Lastly, SMILE has not yet received Food and Drug Administration or Conformité Européenne approval for hyperopic correction, rendering FS-LASIK the choice of procedure for hyperopic correction.

SUMMARY

Both FS-LASIK and SMILE demonstrate good efficacy and predictability. Understanding specific clinical scenarios where one may be superior to the other will aid clinicians in choosing the most suitable procedure for personalized care.

Comparison of visual outcomes and optical aberrations after SMILE with intraoperative Kappa angle adjustments between small and large Kappa angles

This study compares postoperative visual outcomes and optical aberrations after Small Incision Lenticule Extraction (SMILE) in patients with both small (S-Kappa: Kappa angle < 0.2 mm) and large Kappa (L-Kappa: Kappa angle ≥ 0.2 mm) angles. The evaluated aberrations include total higher-order aberrations (HOAs), horizontal coma (HC), vertical coma (VC), and spherical aberrations (SA), with procedures incorporating intraoperative Kappa angle adjustments. We retrospectively analyzed patient records undergoing SMILE utilizing linear mixed models (LMM). We assessed adjusted mean uncorrected distance visual acuity (UDVA), Strehl ratio (SR), total HOAs, VC, and SA at pupils of 3 mm and 6 mm for both S-Kappa and L-Kappa. The disparities between S-Kappa and L-Kappa were evaluated by LMM's adjusted mean differences. The differences in optical metrics were also assessed in eyes grouped by myopia levels: low, moderate, and high. A sensitivity analysis was conducted on a threshold of Kappa angle at 0.3 mm. Eight-five patients (169 eyes) were analyzed, and no significant pre-operative difference was found in UDVA (p = .222) or spherical equivalent (p = .433). Post-operative differences were found in SR at 3 mm pupil size (-0.06, p = .022), total HOA 3 mm (0.15, p = .022), HC 3 mm (0.04, p = .042), VC 3 mm and 6 mm (-0.08, p = .041; 0.04, p = .041). The stratified analysis for high myopia revealed significant differences in UDVA (-0.04, p = .037), HC 3 mm (0.07, p = .03), VC 6 mm (-0.21, p = .001), and SA 3 mm and 6 mm (0.07, p = .037; -0.09, p = .037). Sensitivity analysis showed no significant difference using a 0.3 mm Kappa threshold. While some optical aberrations exhibited statistical differences between S-Kappa and L-Kappa, their clinical significance is limited. Thus, a large Kappa angle might not substantially influence post-operative optical aberrations when intraoperative Kappa angle adjustments are implemented.

Comparison of early visual outcomes after SMILE using VISUMAX 800 and VISUMAX 500 for myopia: a retrospective matched case-control study

VISUMAX 800 was introduced to improve the patient experience and clinical outcomes of small incision lenticule extraction (SMILE). This was a retrospective, matched, and case-control study (1:2) controlled for preoperative central corneal thickness and refractive error that compared early refractive and visual outcomes after SMILE using VISUMAX 800 and VISUMAX 500 to treat myopia. We included 50 eyes that underwent the VISUMAX 800 SMILE and 100 eyes that underwent the VISUMAX 500 SMILE. SMILE using VISUMAX 800 was performed using the CentraLign aid for vertex centration. Cyclotorsion was controlled by an OcuLign assistant in the VISUMAX 800 group after corneal marking. Corneal higher-order aberrations (HOAs) were evaluated using a Pentacam 1 month after surgery. No differences were observed in the pre- and post-operative refractive and visual outcomes at 1 day, 1 month, and 6 months after surgery. VISUMAX 800 induced less total HOAs than VISUMAX 500 (P = 0.036). No statistically significant differences were observed in the amounts of induced spherical aberrations or vertical and horizontal comas. No differences were observed in the 1 month and 6 months refractive and visual outcomes between two SMILE procedures, except for VISUMAX 800, which resulted in lower postoperative total HOAs than VISUMAX 500.

Association of myopia and astigmatism with postoperative ocular high order aberration after small incision lenticule extraction

OBJECTIVE

To investigate the correlation between higher-order aberrations (HOA) after small incision lenticule extraction (SMILE) and the severity of myopia and astigmatism, along with the relevant factors. These findings will provide valuable insights for decreasing the occurrence of HOA after SMILE and enhancing visual quality.

METHODS

A total of 75 patients (150 eyes) with myopia and astigmatism who underwent SMILE were categorized into four groups based on the severity of myopia and astigmatism: Myopia Group 1 (Group M1, spherical diopter ranged from -1.00 D to -4.00 D), Myopia Group 2 (Group M2, spherical diopter ranged from -4.10 D to -10.00 D), Astigmatism Group 1 (Group A1, cylindrical diopter ranged from 0 D to -1.00 D), and Astigmatism Group 2 (Group A2, cylindrical diopter ranged from -1.10 D to -3.00 D). A comprehensive assessment was performed to examine the association between HOA and various relevant factors, including a detailed analysis of the subgroups.

RESULTS

Group M1 had significantly lower levels of total eye coma aberration (CA), corneal total HOA (tHOA), internal tHOA, and vertical CA ( Z 3 - 1 ) after SMILE than Group M2 (P < 0.05). Similarly, Group A1 had significantly lower levels of total eye tHOA, CA, trefoil aberration (TA), corneal tHOA, TA, and vertical TA ( Z 3 - 3 ) after SMILE than Group A2 (P < 0.05). Pearson correlation analysis indicated a statistically significant positive relationship between the severity of myopia/astigmatism and most HOA (P < 0.05). Subgroup evaluations demonstrated a notable increase in postoperative HOA associated with myopia and astigmatism in Groups M2 and A2 compared with the control group. Lenticule thickness, postoperative central corneal thickness (CCT), postoperative uncorrected distance visual acuity (UDVA), and postoperative corneal Km and Cyl were strongly correlated with most HOA. Age, eyes, and postoperative intraocular pressure (IOP) were only associated with specific HOA.

CONCLUSION

HOA positively correlated with the severity of myopia and astigmatism after SMILE. However, this relationship was not linear. HOA after SMILE was influenced by various factors, and additional specialized investigations are required to establish its clinical importance.

Risk Factors for Corneal Monochromatic Aberrations and Implications for Multifocal and Extended Depth-of-Focus Intraocular Lens Implantation

PURPOSE

To discuss factors influencing corneal aberrations that might influence the optical quality after intraocular lens (IOL) implantation.

METHODS

PubMed and Scopus were the main resources used to search the medical literature. An extensive search was performed to identify relevant articles concerning factors influencing the level of corneal aberrations as of August 27, 2023. The following keywords were used in various combinations: corneal, aberrations, defocus, astigmatism, spherical aberration, coma, trefoil, quadrafoil, intraocular lens, and IOL.

RESULTS

Conclusive evidence is lacking regarding the correlation between age and changes in corneal aberrations. Patients with astigmatism have greater corneal higher-order aberrations than those with minimal astigmatism, particularly concerning trefoil and coma. Increased levels of corneal higher-order aberrations are noted following contact lens wear, in patients with dry eye disease, and with pterygium. Increased higher-order aberrations have been reported following corneal refractive surgery and for 3 months following trabeculectomy; regarding intraocular lens surgery, the results remain controversial.

CONCLUSIONS

Several factors influence the level of corneal higher-order aberrations. Multifocal and extended depth-of-focus IOLs can share similarities in their optical properties, and the main difference arises in their design and performance with respect to spherical aberration. Preoperative evaluation is critical for proper IOL choice, particularly in corneas with risk of high levels of aberrations. [J Refract Surg. 2024;40(6):e420-e434.].

Comparative Study of Primary SMILE, SMILE Enhancement, and Femtosecond Laser-Assisted LASIK on Higher Order Aberrations and Corneal Densitometry

PURPOSE

To compare differences in corneal densitometry (CD) and higher order aberrations (HOAs) in eyes that underwent small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) for the treatment of myopia and myopic astigmatism at postoperative months 3, 6, and 12, and to evaluate their changes in a separate cohort of eyes after SMILE enhancement.

METHODS

In this prospective, randomized, paired-eye clinical trial, consecutive eligible participants were randomized to undergo SMILE or FS-LASIK in either eye. Main outcome measures were CD and HOAs preoperatively and at 3, 6, and 12 months postoperatively. A separate cohort of consecutive patients who had SMILE and underwent enhancement were also included for comparison.

RESULTS

For CD, no significant differences were found between SMILE and FS-LASIK up to month 12. For HOA measured by wavefront aberrometry, both SMILE and FS-LASIK had an increase in total root mean square (RMS) HOAs, spherical aberration (SA), and vertical coma up to month 12. SMILE had an additional increase in vertical quatrefoil, and FS-LASIK had an increase in horizontal coma at month 12. FS-LASIK had higher SA than SMILE, whereas SMILE had higher vertical quatrefoil than FS-LASIK at month 12. Central and posterior zone CD had significantly decreased after SMILE enhancement compared to after primary SMILE up to 2 years after enhancement. RMS HOAs, lower order aberrations, and SA were all increased after SMILE enhancement compared to after primary SMILE.

CONCLUSIONS

SMILE induced lower SA but higher vertical quatrefoil than FS-LASIK at 1 year. Both SMILE and FS-LASIK had similar increases in RMS HOAs and vertical coma up to 1 year. There were no differences in CD between both groups. SMILE enhancement additionally had decreased central and posterior CD but greater RMS HOAs and SA compared to primary SMILE. [J Refract Surg. 2024;40(5):e291-e303.].

Clinical outcomes of SMILE and WFG-LASIK used to treat myopia and astigmatism: A systematic review and meta-analysis

PURPOSE

To evaluate the safety, efficacy and postoperative visual quality of small incision lenticule extraction (SMILE) and Wavefront-Guided Laser in situ keratomileusis (WFG-LASIK) and to analyze their efficacy in correcting astigmatism.

METHODS

A systematic literature search was performed using Cochrane Collaboration methodology. Databases searched included PubMed, Embase, the Cochrane Library and Web of Science. RevMan software version 5.3.0 was used for meta-analysis.

RESULTS

A total of 976 eyes were included in 8 studies, of which 539 eyes underwent SMILE and 437 eyes underwent WFG-LASIK. There were no statistically significant differences in the proportion of eyes achieving uncorrected distance visual acuity of 20/20 or better (P=0.18), the proportion of eyes within±0.50 diopter of target refraction postoperatively (P=0.10), or the postoperative magnitude of cylinder (P=0.10). Regarding the Alpins vector analysis of astigmatism, there was no statistically significant difference in the surgical magnitude of error (P=0.09) between the two groups. WFG-LASIK has a lower surgical angle of error (P= 0.002) and higher surgical correction index of cylinder (P=0.03) than SMILE. In terms of aberrations, higher order aberrations (P=0.46), spherical aberrations (P=0.22) and trefoil (P=0.56) were not statistically different, while WFG-LASIK induced less coma than SMILE surgery (P=0.02).

CONCLUSION

Both SMILE and WFG-LASIK are safe and effective ways to correct myopia and astigmatism. Compared with SMILE, WFG-LASIK has a lower surgical angle of error, higher surgical correction index of cylinder and induces less coma.

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/.

Comparative Analysis of Corneal Higher-Order Aberrations after Laser-Assisted In Situ Keratomileusis, Photorefractive Keratectomy, and Small Incision Lenticule Extraction with Correlations to Change in Myopic Q-Value and Spherical Equivalent with and without Astigmatism

Background: This retrospective chart review compared the higher-order aberrations (HOAs) among photorefractive keratectomy (PRK), laser-assisted in situ keratomileusis (LASIK), and small incision lenticule extraction (SMILE) alongside changes in spherical equivalent (SEQ) and corneal shape (Q-value). Methods: Analyzing 371 myopic eyes, including 154 LASIK, 173 PRK, and 44 SMILE cases, Pentacam imaging was utilized pre-operatively and at one-year post-operative visits. Results: All procedures resulted in 100% of patients achieving an uncorrected distance visual acuity (UDVA) of 20/40 or better, with 87% of LASIK and PRK, and 91% of SMILE patients having 20/20 or better. Significant increases in HOAs were observed across all procedures (p < 0.05), correlating positively with SEQ and Q-value changes (LASIK (0.686, p < 0.05), followed by PRK (0.4503, p < 0.05), and SMILE (0.386, p < 0.05)). Vertical coma and spherical aberration (SA) were the primary factors for heightened aberration magnitude among the procedures (p < 0.05), with the largest contribution in SMILE, which is likely attributed to the centration at the corneal apex. Notably, PRK showed insignificant changes in vertical coma (-0.197 µm ± 0.0168 to -0.192 µm ± 0.0198, p = 0.78), with an increase in oblique trefoil (p < 0.05). Conclusions: These findings underscore differences in HOAs among PRK, LASIK, and SMILE, helping to guide clinicians.

The Association Between Ocular Residual Astigmatism and the Efficacy of Astigmatism Correction Via Small Incision Lenticule Extraction (SMILE)

INTRODUCTION

Astigmatism correction after small-incision lenticule extraction (SMILE) surgery is affected by several factors, including ocular residual astigmatism (ORA), which accounts for the vector difference between refractive and corneal astigmatism. Previous studies revealed the relationship between ORA and astigmatism correction after laser-assisted in situ keratomileusis (LASIK). However, in SMILE surgery, no comprehensive study exploring the link between these two variables has been performed. We have therefore assessed the association between ORA and astigmatism correction after SMILE.

METHODS

This was a retrospective, single-centered study. Patients with myopia or myopic astigmatism who underwent SMILE surgery using the 500-kHz Visumax laser platform and were followed up for at least 3 months were included. Patients' demographic and clinical characteristics, such as visual acuity, refractive status and corneal tomography, were recorded. ORA was calculated using Alpins Statistical System for Ophthalmic Refractive Surgery Techniques (ASSORT) Ocular Residual Astigmatism calculator.

RESULTS

A total of 888 eyes (408 eyes from males and 480 eyes from females) from 444 patients (mean age [standard deviation] 32.4 ± 7.1 years) were included in our study. Mean (± SD) preoperative sphere and cylinder were - 5.45 ± 1.98 (range - 10.00-0.00) diopter (D) and - 0.89 ± 0.70 (range - 4.00-0.00) D, respectively. Calculated mean ORA was 0.68 ± 0.35 (range 0.07-3.53) D. Postoperative logMAR uncorrected visual acuity was 0.03 ± 0.31. Mean postoperative sphere and cylinder were - 0.10 ± 0.56 (range - 1.5 to 1.0) D and - 0.51 ± 0.37 (- 1.5 to 0.0) D, respectively. The Pearson correlation test revealed preoperative sphere, steep keratometry (steep-K) and ORA were statistically correlated with the amplitude of astigmatism correction (P < 0.001), and the generalized estimating equations analysis showed that ORA was negatively correlated with the amplitude of astigmatism correction (P < 0.001).

CONCLUSION

The results of our study suggest that preoperative higher ORA may be associated with a lower magnitude of astigmatism correction after SMILE surgery in patients with all levels of astigmatism preoperative.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT05604872. Registered 3 November 2022-Retrospectively registered. https://clinicaltrials.gov/ct2/show/NCT05604872.

One-year clinical efficacy evaluation of selective corneal wavefront aberration-guided FS-LASIK correction in patients with high myopia

AIM

To evaluate the effectiveness, safety, predictability, precision and changes of higher-order aberrations (HOAs) on corneal front surface of selective corneal wavefront aberration-guided femtosecond laser-assisted in situ keratomileusis (CW-FS-LASIK) in patients with high myopia 1-year postoperatively.

METHODS

Totally 74 eyes of 37 patients with high myopia or myopic astigmatism in both the eyes who underwent the CW-FS-LASIK procedure in Xi'an Gaoxin Hospital from January 2021 to June 2021 were included. The changes of uncorrected distance visual acuity (UDVA), best corrected visual acuity (BCVA), spherical equivalent refraction (SER), astigmatism, HOAs and Strehl ratio (SR) on the anterior surface of the cornea after 1y of the surgery were analyzed.

RESULTS

At postoperative 1y, the UDVA (logMAR) of 74 eyes (100%) reached 0 or better, including 0 in 8 eyes (10.81%), -0.1 in 45 eyes (60.81%), and -0.2 in 21 eyes (28.38%). The effectiveness index was 1.29±0.134. There was no decrease in postoperative BCVA compared with preoperative BCVA in all patients. Postoperative BCVA was the same in 44 eyes (59.46%) as preoperative BCVA, increased by 1 line in 23 eyes (31.08%) and increased by 2 lines in 7 eyes (9.46%) compared with preoperative BCVA. The safety index was 1.11±0.159. The estimated corrected SER before surgery was (-7.76±1.21) D, and the actual corrected SER was (-7.83±1.25) D (Y=0.9811X+0.2156, R2=0.9084). There was a high correlation between the estimated corrected SER and the actual corrected SER. The postoperative SER in 74 eyes (100%) was within ±0.75 D. The postoperative astigmatism of all was within -0.75 D to 0. Root mean square (RMS) HOAs of spherical aberration and SR within 5 mm of the corneal front surface were all increased compared with those before operation (P<0.01). The total coma, horizontal coma and vertical coma were all decreased compared with those before operation (P<0.01). There was no statistically significant difference in horizontal trefoil and vertical trefoil compared with preoperative ones (P>0.05).

CONCLUSION

Selective CW-FS-LASIK for correction of high myopia is effective, safe, predictive, and accurate. For patients with preoperative RMS HOAs over 0.25 defocus equivalent, postoperative coma aberration can be significantly reduced, and SR value can be increased, thus corneal imaging quality can be improved.

Comparing Visual Outcomes of Light Adjustable Intraocular Lenses in Patients With and Without Prior History of Corneal Refractive Surgery

PURPOSE

To assess visual outcomes of light adjustable intraocular lens (LAL; Calhoun Vision, Inc) implantation after cataract extraction in patients with a history of corneal refractive surgery.

METHODS

The records of patients who received LALs with and without a history of corneal refractive surgery were retrospectively reviewed. Data for 51 eyes (30 patients) with a history of corneal refractive surgery and 52 eyes (44 patients) without refractive surgery were analyzed. A total of 36 eyes of patients with and 43 eyes of patients without a history of corneal refractive surgery had 12-month follow-up data available. The primary outcomes evaluated were uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA).

RESULTS

At 12 months, 31% of eyes with a history of corneal refractive surgery had a UDVA of 20/20 or better and 97% of eyes were 20/40 or better. In contrast, 63% of patients with no history of corneal refractive surgery had 20/20 UDVA or better at 12 months and 100% were 20/40 or better. Of patients with a history of corneal refractive surgery, 55% and 83% of eyes at 12 months were within ±0.50 and ±1.00 diopters, respectively, of the target refraction compared to 89% and 96% of eyes without a history of corneal refractive surgery.

CONCLUSIONS

LALs are a promising platform for achieving excellent visual outcomes following cataract surgery. Patients with a prior history of corneal refractive surgery can achieve excellent visual outcomes with the LAL. However, this study found that patients with a history of corneal refractive surgery demonstrated less predictable visual acuity outcomes when compared to patients without a history of corneal refractive surgery. [J Refract Surg. 2023;39(5):311-318.].

Small Incision Lenticule Extraction (SMILE) Versus Laser Assisted Stromal In Situ Keratomileusis (LASIK) for Astigmatism Corrections: A Systematic Review and Meta-analysis

PURPOSE

To compare small incision lenticule extraction (SMILE) and laser assisted stromal in situ keratomileusis (LASIK) for astigmatism correction.

DESIGN

Systematic review and meta-analysis METHODS: We reviewed published studies comparing outcomes after LASIK and SMILE for astigmatism correction by querying PubMed, EMBASE, Cochrane, and Web of Science, with a cut-off date of September 3, 2022. We also compared the changes in visual acuity, refraction, and high-order aberrations between the surgeries. Astigmatism correction outcomes in the low-to-moderate group (less than or equal to -2.00 D) and high group (greater than -2.00 D) were evaluated using vector analysis. The Cochrane risk of bias tool in RevMan software was used for randomized studies (RCT), and Risk Of Bias In Nonrandomized Studies - of Interventions (ROBINS-I) was used for the nonrandomized studies (NRSs).

RESULTS

There were 17 studies (5 randomized studies and 12 cohort studies), including 1,985 eyes. A statistically significant difference was found in the correction index (mean difference [MD] = -0.02, 95% confidence interval [CI] = -0.04 to -0.01, P =0.01), although there was no significant difference in the index of success (MD = 0.01, 95% CI = -0.03 to 0.05, P =0.51), different vector (MD = 0.07, 95% CI = 0.00 to 0.13, P =0.04), and angle of error (MD = 0.56, 95% CI = -0.34 to 1.45, P =0.22) between SMILE and LASIK. However, for low-to-moderate astigmatism correction, SMILE exhibited a smaller correction index (MD = -0.08, 95% CI= -0.13 to -0.02, P =0.008) and a larger difference vector (MD = 0.18, 95% CI = 0.09 to 0.27, P <0.0001) than LASIK. There was no significant difference between the different procedures in visual acuity and refraction (spherical equivalent: MD = -0.04, 95% CI = -0.08 to 0.01, P =0.15) or high-order aberration (MD = -0.01, 95% CI = -0.07 to 0.04, P =0.67), except spherical aberration (MD = -0.12, 95% CI = -0.23 to -0.01, P =0.04). The risk of bias was moderate in most studies because of poor reporting of several bias domains for RCTs, and because of confounding and selective outcome reporting for NRSs.

CONCLUSIONS

When used to treat severe astigmatism, both SMILE and LASIK provide effective and predictable results and generally have equivalent outcomes. However, evidence reveals a tendency toward undercorrection in the SMILE groups for astigmatism correction. In addition, LASIK has a greater probability of causing postoperative spherical aberration.

Bilateral sequential small-incision lenticule extraction and LASIK result in similar short-term quality-of-life outcomes

PURPOSE

To compare quality of life (QoL) between patients who receive bilateral small-incision lenticule extraction (SMILE) or laser in situ keratomileusis (LASIK) vs bilateral sequential SMILE-LASIK (BSSL) surgery.

SETTING

Singapore National Eye Centre, Singapore.

DESIGN

Retrospective cohort study.

METHODS

2 patient cohorts were recruited (2010-2012; 2014-2016). The bilateral SMILE (BS) and bilateral LASIK (BL) groups comprised patients (mean ± SD age: 30.3 ± 6.5, 50% male) from a prospective nonrandomized study who chose SMILE and LASIK, respectively. The BSSL group comprised patients (mean ± SD age: 28.6 ± 6.2, 64.3% male) randomized to receive SMILE in 1 eye and LASIK in the other. Rasch-scaled scores of the QoL Impact of Refractive Correction questionnaire between groups postoperatively at 1 and 3 months were compared.

RESULTS

At month 1, scores on 3 QoL without emotional well-being items were worse in the BSSL (n = 70) compared with the BL group (n = 25), specficially, "using sunglasses" (β: -20.6, 95% CI, -34.3 to -6.9), "reliance on refractive correction" (-23.1, 95% CI, -40.9 to -5.4), and "medical complications from optical correction" (β: -14.8, 95% CI, -27.9 to -1.7). Emotional well-being (overall), and items "feeling able to do things" (β: 11.0, 95% CI, 1.6-20.4) and "feeling eager to try new things" (β: 14.1, 95% CI, 3.6-24.6) were better in the BSSL compared with the BS group (n = 25). No substantive differences were observed at month 3.

CONCLUSIONS

Refractive correction-related QoL differences at month 1 between BSSL and BS/BL patients attenuated by month 3. Bilateral sequential SMILE-LASIK surgery appeared unlikely to negatively affect QoL beyond 3 months.

Clinical outcomes and higher order aberrations of wavefront-guided LASIK versus SMILE for correction of myopia: A systemic review and meta-analysis

To systematically evaluate the clinical effect of wavefront-guided laser in situ keratomileusis (WFG-LASIK) and small incision lenticule extraction (SMILE) in terms of refractive errors and high-order aberrations. A systematic literature search of PubMed, EMBASE, the Cochrane Library, Web of Science and China National Knowledge Internet was performed to identify studies evaluating the clinical outcomes of SMILE and WFG-LASIK ended in May 2022. Meta-analyses were performed according to the PRISMA guidelines. The risk of bias of the RCTs was evaluated using the Cochrane Handbook criteria, and the quality of the non-randomised controlled studies was assessed using the Newcastle-Ottawa Scale. In total, 1385 eyes (SMILE group, 750 eyes; WFG-LASIK group, 635 eyes) from 12 studies were included. The meta-analysis demonstrated that spherical aberration was smaller in the SMILE group than in the WFG-LASIK group (standardised mean difference [SMD]: -0.34, 95% confidence interval [CI]: -0.47, -0.22; p < 0.00001), and that the postoperative values of vertical coma (SMD: 0.83; 95% CI: 0.63, 1.03; p < 0.00001) and trefoil (SMD: 0.37; 95% CI: 0.02, 0.72; p = 0.04) were higher in the SMILE group compared to the WFG LASIK group. There were no significant differences in the clinical outcomes and the values of induced total higher order aberrations between the WFG-LASIK and SMILE groups (SMD: 0.05; 95% CI: -0.09, 0.19; p = 0.47). Both SMILE and WFG-LASIK were found to be safe, effective, and predictable. SMILE may induce more vertical coma and trefoil, whereas WFG LASIK may induce more spherical aberrations, but no significant differences were found in the total higher order aberrations between SMILE and WFG-LASIK.

Comparison of Postoperative Safety, Efficacy, and Visual Quality after SMILE for Myopic Patients with Different Corneal Thicknesses

PURPOSE

To investigate the safety, efficacy, and visual quality of small incision lenticule extraction (SMILE) in different corneal thickness patients with myopia or myopic astigmatism.

METHODS

This prospective cohort study included 191 right eyes of 191 patients. Eyes were divided into three groups according to preoperative central corneal thickness (CCT) (Preoperative central corneal thickness (CCT) was the group indicator.) There were 31 eyes in the thin cornea group (CCT ≤500 um (μm), TC), 94 eyes in the moderate corneal thickness group (CCT ≥501 um (μm) and ≤550 um (μm), MD) and 66 eyes in the thick cornea group (CCT ≥550 um (μm), TK). Comparisons in uncorrected (UDVA) and best-corrected distance visual acuity (BDVA), manifest refractive spherical equivalent (SE), preoperative mesopic/photopic contrast sensitivity (CS), ocular higher-order aberrations (HOAs) at a 6mm analytical pupil diameter, and visual quality questionnaires were made (performed) among the three groups during the postoperative six months. Subgroup analyses were made based on preoperative SE.

RESULTS

The safety indices at six months were 1.15 ± 0.18, 1.14 ± 0.17, and 1.18 ± 0.17, respectively (p = 0.374), and the efficacy indices at six months were 1.07 ± 0.25, 1.12 ± 0.22, and 1.11 ± 0.21, respectively (p = 0.599). The postoperative SE was -0.07 ± 0.52D, -0.14 ± 0.38D, and -0.05 ± 0.46D after SMILE in the three groups, respectively (p = 0.376). No significant difference was found in mesopic/photopic CS, HOAs, and visual quality among different corneal thickness groups and SE groups. Postoperative SE and efficacy indices were the lowest in thin cornea eyes with ultra-high myopia (over -9.00 D).

CONCLUSIONS

SMILE provides comparable safety, efficacy, and visual quality results in different corneal thickness patients. Those with myopia higher than -9.00 D had less efficacy after surgery, especially in thin cornea patients.

Evaluation of Higher Order Aberrations and Anterior Segment Parameters Changes After Implantable Collamer Lens Implantation for High Myopia

Purpose

To evaluate changes in higher order aberrations (HOAs) induced by implantable collamer lens (ICL) implantation in correction of high myopia and to compare the anterior segment parameters before and after surgery. Also, to correlate these parameters with HOAs, the best corrected visual acuity (BCVA) and intraocular pressure (IOP).

Methods

This prospective interventional cohort case series study included 40 eyes with high myopia that underwent ICL V4c implantation. They were evaluated pre-operatively and post-operatively at 1^st and 3^rd month HOAs using Scheimpflug Sirius Camera. The anterior segment parameters were evaluated by optical biometry. Correlations between HOAs, BCVA and anterior segment parameters were evaluated.

Results

The mean pre-operative BCVA was 0.67 ± 0.17, while post-operative BCVA was 0.74 ± 0.16 (p-value < 0.001). The spherical equivalent was -13.66 ± 2.23 pre-operatively, while post-operatively it was -0.77 ± 0.65 (p-value < 0.001). The mean pre-operative root mean square (RMS) of HOAs was 0.62 ± 0.11 µm, while mean post-operative RMS in the 1st month was 0.82 ± 0.29 µm (p-value < 0.001). At 3rd month, it was 0.63 ± 0.17 µm (p-value = 0.685). The mean pre-operative anterior chamber depth (ACD) was 3.66 ± 0.26 mm. It decreased in the post-operative 1^st month to 3.46 ± 0.30 mm, while in 3^rd month 3.45 ± 0.24 mm (p-value < 0.001, < 0.001) respectively. The mean pre-operative anterior chamber angle (ACA) 45.98 ± 8.39 ^o while, the mean ACA was 31.65 ± 4.14, 31.03 ± 3.74 post-operatively (p-value < 0.001, < 0.001) respectively. There was significant increase in IOP (p-value < 0.001).

Conclusion

ICL implantation is safe and effective in correction of high myopia, as HOAs increase at first month post-operatively then, return to the pre-operative level by 3^rd month. However, anterior segment parameters show significant changes which may need longer follow up.

Comparison of Changes in Corneal Thickness and Curvature After Myopia Correction Between SMILE and FS-LASIK

PURPOSE

To comparatively investigate the changes in corneal thickness and curvature between small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK).

METHODS

Data were collected preoperatively and postoperatively at 1 week, 1 month, and 3 months, including central corneal thickness (CCT), midperipheral corneal thickness (MPCT), peripheral corneal thickness (PCT), central keratometry (CK), midperipheral keratometry (MPK), and peripheral keratometry (PK), using a dual rotating Scheimpflug analyzer.

RESULTS

At 1 week postoperatively, changes in CCT, MPCT, PCT, and PK were significantly greater in the SMILE group than in the FS-LASIK group (P = .003 for CCT and < .001 for MPCT, PCT, and PK), but no significant inter-group differences were found between changes in CK and MPK (P = .883 and .513, respectively). CCT, MPCT, and PK values showed a similar increase in both groups, but significantly more increase in PCT and significantly less increase in CK and MPK was observed in the SMILE group from 1 week to 3 months after surgery. At 3 months postoperatively, CCT and MPCT were significantly thinner in the SMILE group than in the FSLASIK group (P = .018 and .022, respectively), and there was no significant difference in PCT, CK, MPK, and PK between the two groups.

CONCLUSIONS

SMILE caused significantly more corneal thinning at the center, midperiphery, and periphery, and more corneal flattening at the periphery, compared to FS-LASIK. A different pattern of corneal remodeling was observed between the two surgeries during the 3-month follow-up period. [J Refract Surg. 2023;39(1):15-22.].

Evaluating early-stage disk halo changes after small incision lenticule extraction

PURPOSE

To investigate early changes in the disk halo under different light conditions after myopic small incision lenticule extraction (SMILE).

METHODS

This prospective study included 70 eyes of 70 myopic patients aged 18-33 years, with a spherical equivalent (SE) of -5.87 ± 1.86 D, who underwent SMILE. The subjective refraction, higher-order aberrations (HOAs), pupillometry, and halo were measured preoperatively and postoperatively to analyse disk halo variations and correlated factors.

RESULTS

At 5 cd/m2 and 1 cd/m2 luminance, the halo radius in the high myopia (HM) group reached a postoperative peak after 1 week (p = 0.000 and 0.019, respectively), and recovered to baseline after 3 months. In the low-to-moderate (LM) myopia group, the halo radius did not differ 1 week postoperatively compared to the preoperative level (p = 0.015), but significantly improved after 3 months (p = 0.000). The halo radius correlated with SE, uncorrected distance visual acuity (UDVA), ocular HOAs, coma, and the pupillary light reflex in the LM group at all time points, but there were no correlations in the HM group.

CONCLUSIONS

Halo symptoms occurred early after SMILE, but recovered within 3 months. The recovery process was slower in the HM group than in the LM group, and the halo radius correlated with SE, UDVA, ocular HOAs, coma, and the pupillary light reflex.

Corneal opacities after small-incision lenticule extraction

A 36-year-old woman was referred to our clinic in October 2021 with suboptimal vision at intermediate and near distances and halos and photophobia after a small-incision lenticule extraction (SMILE) in December 2019. The patient needs to increase font size of her computer to 150% to read text, but images still appear blurred. She indicates that sunglasses seem to improve her contrast. Preoperatively, her refractive error was -2.5 diopters (D) and -2.25 D for right and left eyes. The optical zone size of the SMILE procedure was 6.8 mm. There is no further information available on the peroperative course of the SMILE procedure. Her uncorrected distance visual acuity (UDVA) is 20/20 in both eyes and does not improve with correction. The Schirmer tear test is 14 to 13 mm. Slitlamp biomicroscopy of the right eye and the left eye reveals hyperreflective small opacities in the anterior one-third of the corneal stroma ( Figures 1 and 2JOURNAL/jcrs/04.03/02158034-202209000-00021/figure1/v/2022-08-29T115553Z/r/image-tiffJOURNAL/jcrs/04.03/02158034-202209000-00021/figure2/v/2022-08-29T115553Z/r/image-tiff ). No other abnormalities are seen. The scotopic pupil sizes are 6.41 and 6.73 mm. Straylight measurements are within normal limits. Higher-order aberrations (HOAs) measure for the right eye (6.03 mm pupil) 0.818 μm and for the left eye (6.17 mm pupil) 0.560 μm. The corneal Scheimpflug tomography quad maps for both eyes are shown in Supplemental Figures 1 and 2 ( http://links.lww.com/JRS/A663 , http://links.lww.com/JRS/A664 ). What is your diagnosis or are additional diagnostic methodologies needed to establish a diagnosis? What is your treatment advice for this patient?

Corneal morphological changes after small incision lenticule extraction for myopic anisometropia

Purpose

This research aims to study the corneal morphological changes in adult patients with myopic anisometropia after small incision lenticule extraction (SMILE) and the safety, efficacy, and predictability of clinical outcomes.

Methods

This was a prospective cohort study. Patients with myopic anisometropia [refractive difference &gt;2.0 diopters (D)] were included in this study who underwent SMILE at our hospital from September 2019 to March 2021. For the two eyes of each patient, the one with higher myopia was defined as group A, and the fellow eye was group B. The follow-up time points were set as 1 week, 1 month, 3 months, and 6 months after the surgery. The data collected were uncorrected and best-corrected distance visual acuity (UDVA and CDVA), spherical equivalent (SE), efficacy and safety indexes, posterior corneal elevation (PCE), anterior and posterior corneal radius of curvature in the 3 mm area at the center of the thinnest point of the cornea (ARC and PRC), and higher-order aberrations (HOAs).

Results

The study included 36 patients (72 eyes), and the mean age was 25.2 ± 6.4 years. The preoperative SEs were −6.45 ± 1.25 D in group A and −3.76 ± 1.29 D in group B. Six months after surgery, the SEs in groups A and B were −0.09 ± 0.50 D and 0.07 ± 0.47 (P = 0.059), respectively. The efficacy indexes were 1.06 ± 0.16 in group A and 1.07 ± 0.14 in group B (P = 0.750). The safety indexes were 1.08 ± 0.14 in group A and 1.12 ± 0.15 in group B (P = 0.173). The PCE was significantly reduced at 6 months after surgery in pagebreak both groups (P &lt; 0.05). The ARC was significantly higher than before the surgery (P &lt; 0.05) in the two groups. The two groups showed significant increases in total HOAs, coma 90°, and spherical aberrations (P &lt; 0.05).

Conclusion

SMILE is predictable, effective, and safe in correcting myopic anisometropia. The postoperative changes in HOAs are characteristic.

Wavefront aberrations caused by biomechanical effects after Small Incision Lenticule Extraction (SMILE) based on finite element analysis

To examine wavefront aberrations induced by biomechanical effects after Small Incision Lenticule Extraction (SMILE) surgery. The three-dimensional (3D) finite element models of the human eye were established. By loading the intraocular pressure (IOP), the displacement of the anterior and posterior surface of the cornea was calculated. Then the displacement was converted into the wavefront aberrations by wave-surface fitting. The results showed that the induced wavefront aberrations were noticeable from biomechanical effects after SMILE surgery. The induced higher-order aberrations from the anterior corneal surface included spherical aberration, y-Trefoil, and x-Tetrafoil. Spherical aberration was positively correlated with corrected diopter (D), but x-Tetrafoil and y-Trefoil remained stable. The induced wavefront aberrations from the posterior corneal surface were smaller than those from the anterior corneal surface, and some of the aberrations compensated each other. With IOP increased, defocus and x-Tetrafoil from the anterior corneal surface increased, while y-Trefoil and spherical aberration decreased. The IOP only affected defocus from the posterior corneal surface. In addition, the incision size also had a distinct impact on primary x-astigmatism and x-Trefoil from the anterior corneal surface, and it had a smaller effect on the aberrations from the posterior corneal surface. Therefore, the biomechanical effects increased residual wavefront aberrations after SMILE refractive surgery.

Prospective, Randomized Contralateral Eye Comparison of Wavefront-Guided Laser In Situ Keratomileusis and Small Incision Lenticule Extraction Refractive Surgeries

PURPOSE

Wavefront-guided laser in situ keratomileusis (WFG-LASIK) and small incision lenticule extraction (SMILE) are keratorefractive surgeries that can improve uncorrected visual acuity in myopic patients. Comparison of visual outcomes in myopic patients treated with LASIK and SMILE is needed.

DESIGN

Prospective, randomized contralateral eye-controlled trial.

METHODS

We performed a single-center prospective, randomized contralateral eye comparison of WFG-LASIK and SMILE (NCT03067077). Myopic patients with low levels of astigmatism were treated with WFG-LASIK in one eye and SMILE in the fellow eye from March 2017 to March 2021. Treatments were randomized by ocular dominance. WFG-LASIK and SMILE were performed. Postoperative evaluation at 1 day consisted of uncorrected distance visual acuity (UDVA), wavefront aberrometry, and a slit-lamp examination. On subsequent postoperative visits at 1 month, 3 months, 6 months, and 12 months, UDVA, manifest refraction, 5% and 25% low-contrast visual acuity, wavefront aberrometry, and slit-lamp examination were performed.

MAIN OUTCOME MEASURE

The primary outcome measure was UDVA at 12 months.

RESULTS

Eighty-eight eyes of 44 patients with myopia were enrolled in the study. Seventy-four eyes of 37 patients had successful treatments and completed 12 months of follow-up. At postoperative month 12, there were a significantly higher proportion of WFG-LASIK eyes that had ≥20/20 UDVA compared with SMILE eyes (94% vs 83%, P < .05). There was no difference between spherical equivalent between WFG-LASIK eyes and SMILE eyes (-0.17 ± 0.25 vs -0.29 ± 0.38, P > .05); there was no difference in higher order aberrations, including coma, trefoil, and spherical aberrations (P > 0.05); and there were a significantly higher proportion of WFG-LASIK eyes that had improved 5% and 25% low-contrast visual acuity compared with SMILE eyes (P < 0.05).

CONCLUSIONS

WFG-LASIK and SMILE both offered marked improvements in corrected distance visual acuity and excellent predictability in both eyes. Compared with SMILE, WFG-LASIK resulted in faster visual recovery, better low-contrast visual acuity, and greater gains in uncorrected visual acuity.

Comparison of Corneal Optical Quality After SMILE, Wavefront-Optimized LASIK and Topography-Guided LASIK for Myopia and Myopic Astigmatism

Purpose

To compare visual outcomes and corneal optical quality after small incision lenticule extraction (SMILE), wavefront-optimized (WFO) FS-LASIK, and topography-guided customized ablation treatment (TCAT) FS-LASIK for myopia.

Methods

This prospective case-series study included 283 eyes of 283 myopic patients who underwent SMILE or FS-LASIK. There were 102, 100, and 81 eyes in the SMILE group, WFO group and TCAT group, respectively. The tomography system (Sirius) was used to measure corneal aberrations and optical quality.

Results

At postoperative 1 and 6 months, there were no significant differences in uncorrected distance visual acuity and corrected distance visual acuity among the three groups (P > 0.05). Postoperative manifest refractive spherical equivalent was similar among the groups (P > 0.05). There was statistically significant difference in cylinder at 1 month among the three groups, with the highest mean value in TCAT group (P < 0.05). The corneal optical path difference, root mean square of corneal astigmatism and strehl ratio were the most superior in the TCAT group at postoperative 1 and 6 months (P < 0.05).

Conclusion

SMILE, WFO FS-LASIK, and TCAT FS-LASIK provided similar visual results. The corneal visual quality after TCAT FS-LASIK was the best.

Long-Term Observation of Higher-Order Aberrations and Microdistortions in Bowman’s Layer After Small Incision Lenticule Extraction for the Correcting Myopia With Spherical Equivalent Higher Than −9.0 Diopters

Purpose

To evaluate the outcomes in corneal higher-order aberrations (HOAs) and microdistortions in the Bowman’s layer after femtosecond laser small incision lenticule extraction (SMILE) for correcting extremely high myopia.

Methods

This prospective study included patients with myopia with spherical equivalent ≥ -9.0 Diopters (D). SMILE was performed in forty eyes of 40 patients. Pentacam was used to evaluate HOAs before and at 1 day, 3 months, 6 months, and 2 years after surgery. Fourier-domain optical coherence tomography was used to evaluate microdistortions at 2 years postoperatively. Thirty-two eyes of 32 patients receiving femtosecond laser-assisted in situ keratomileusis (FS-LASIK) were enrolled as the control group. HOAs were measured before, at 1 day and at least 1 year postoperatively.

Results

After SMILE, the long-term safety and effectiveness index was 1.25 and 0.85, respectively. Microdistortions were observed in 73.5% of the eyes at 2 years, with an average number of 1.20 ± 1.22 microdistortions and an average width of 287.37 ± 259.00 μm. We detected more microdistortions in the horizontal meridian than in the vertical meridian (p = 0.035). The average number and width of microdistortions were both higher in the central region (≤4 mm) than in the peripheral region (4–8 mm) (both p < 0.001). With the exception of horizontal trefoil in the SMILE group and vertical trefoil in the FS-LASIK group, significant changes over time were observed in all other HOAs (all p < 0.05). Meanwhile, we detected significant increases in the total corneal HOA, spherical aberration (SA), and coma at all time-points after both surgeries (all p < 0.01). Compared with FS-LASIK, SMILE induced less SA (p < 0.001) and more horizontal coma (p = 0.036). In the SMILE group, the HOA, SA, and trefoil were more in the small optical zone (≤6.0 mm) than in the large optical zone (>6.0 mm) (all p < 0.05). The increase in SA and most trefoil correlated with the mean number of central microdistortions number (all p < 0.05).

Conclusion

For myopia over −9.0D, the microdistortions in the Bowman’s layer were still detectable in most eyes long-term after SMILE. Both SMILE and FS-LASIK induced more HOAs, mainly HOA, SA, and coma. The small optical zone and microdistortions may affect postoperative aberrations.

Comparison of clinical outcomes of LASIK, Trans-PRK, and SMILE for correction of myopia

Transepithelial photorefractive keratectomy (Trans-PRK), laser-assisted in situ keratomileusis (LASIK), and small incision lenticule extraction (SMILE) are three mainstay refractive surgeries worldwide. The applicability, efficacy, safety, and predictability of these different techniques are quite similar. Trans-PRK has the strongest biostability, earliest return to normal corneal sensitivity but the longest recovery time, most uncomfortable postoperative experience, and possibility of corneal haze. LASIK possesses the fastest visual rehabilitation but the slowest corneal nerve reinnervation, and flap displacement is possibly lifelong. SMILE incurs no flap-related complications and has intermediate vision recovery time and biomechanics compared with Trans-PRK and LASIK. However, it lacks the cyclotorsion-compensation system, eye-tracking system, and customized treatment profile for high astigmatism or irregular corneal surface. This review aims to introduce the mechanisms, pros, and cons of these three types of refractive surgery. With full understanding, practitioners could advise patients on the most suitable treatment of choice.

Assessment of the correlation of the tear breakup time with quality of vision and dry eye symptoms after SMILE surgery

Purpose

It is well reported that dry eye symptoms can increase after many refractive surgery procedures. This study aims to provide a clinical understanding of the correlation of fluorescein tear film breakup time (FTBUT) with quality of vision (QoV) and dry eye symptoms following small incision lenticule extraction surgery (SMILE).

Methods

Patients electing to have SMILE surgery were subdivided into 2 groups: Group 1 included short preoperative FTBUTs of 3 to 6 seconds (s); Group 2 included long FTBUTs of ≥ 8 s. Uncorrected distance visual acuity, corrected distance visual acuity, manifest refraction, FTBUT, QoV and Ocular Surface Disease Index (OSDI) questionnaires were recorded 1 and 6 months postoperatively.

Results

Thirty-nine subjects were included in each group. There was no significant difference in visual outcomes between the 2 groups at both the 1- and 6-month postoperative assessments. FTBUT remained significantly lower in group 1. Oxford staining was initially higher for group 1 at 1 month (P = 0.007), but there was no significant difference at 6 months (P = 0.180). There was no significant difference in QoV or OSDI scores between the 2 groups at both postoperative visits.

Conclusions

Low preoperative FTBUT (3–6 s) does not appear to negatively affect postoperative visual outcomes or results in a greater likelihood of dry eye symptoms and poor ocular surface compared to eyes with a longer preoperative FTBUT. These results suggest that a low preoperative FTBUT does not necessarily increase the likelihood of poor visual acuity, dry eyes symptoms, or poor ocular surface outcomes following SMILE surgery.

Factors associated with corneal high-order aberrations before and after femtosecond laser-assisted in situ keratomileusis

Background

Corneal high-order aberrations (HOAs) are related to visual quality. However, the factors associated with corneal HOAs before and after femtosecond laser-assisted in situ keratomileusis (FS-LASIK) have not yet been elucidated. The aim of this study is to observe the factors related to corneal HOAs before and after FS-LASIK.

Methods

Prospective observational study was designed to measure corneal HOAs in 149 eyes of 75 patients before and 6 months after FS-LASIK. The relationship between spherical diopter and corneal parameters, including K1 and K2 (horizontal and vertical refractive power of the cornea, respectively), the aspheric characteristics of the cornea (Q), mean radius of the curvature of the cornea (Rm), and central corneal thickness (CCT), with corneal HOAs were analyzed.

Results

The spherical diopter was correlated with trefoil at 30° before surgery and with vertical coma, four-order astigmatism at 0°, trefoil at 30°, spherical aberration, and six-order spherical aberration after surgery (P<0.05). CCT was correlated with vertical coma, four-order astigmatism at 0°, trefoil at 30°, and six-order spherical aberration after surgery (P<0.05). K1 was correlated with spherical aberration and six-order astigmatism at 0° before surgery (P<0.05). K2 was correlated with spherical aberration, six-order astigmatism at 45°, astigmatism at 0°, six-order astigmatism at 0° before surgery, and trefoil at 30° after surgery (P<0.05). Q was correlated with spherical aberration, six-order spherical aberration, and six-order astigmatism at 45° (P<0.05). Rm was correlated with six-order astigmatism at 0°, spherical aberration, six-order astigmatism at 45° before surgery, and astigmatism at 0° after surgery (P<0.05)

Conclusions

Corneal parameters and spherical diopter are related to the HOAs of the cornea before and after FS-LASIK.

Matched comparison of corneal higher order aberrations induced by SMILE to femtosecond assisted LASIK and to PRK in correcting moderate and high myopia: 3.00mm vs. 6.00mm

Background

The refractive surgeries induce corneal higher order aberrations (C-HOAs). In this study, change of C-HOAs after small-incision lenticule extraction (SMILE) compared to femtosecond assisted laser in situ keratomileusis (femto-LASIK), and to photorefractive keratectomy with mitomycin-C (PRK) under photopic and mesopic conditions.

Methods

In this prospective study, age, gender, and apical corneal thickness (ACT) matched cases with moderate myopia [spherical equivalent (SE) 3.00 to 6.00D) to high myopia (SE > 6.00D)] were enrolled. In addition to visual acuity and refraction, total C-HOA, coma, spherical aberration (SA), and trefoil in the 3- and 6-mm zones were measured before and 3 and 6 months after surgery.

Results

Overall, 372 moderate myopia cases (124 eyes of 124 individuals in each surgical group) and 171 high myopia cases (57 eyes of 57 individuals in each surgical group) were enrolled. At baseline, the differences in age, gender, ACT, uncorrected and corrected visual acuity, and SE were not statistically significant between subgroups of surgical methods within each myopia group (all P > 0.05). At 12 months, in the moderate myopia group, there was less increase in 6-mm zone total C-HOA, coma, and SA with SMILE compared to the other groups (all P < 0.05). In the high myopia group, there was greater increase in photopic total C-HOA and trefoil and less increase in mesopic SA with SMILE (all P < 0.05).

Conclusions

In correction of moderate myopia, SMILE has better results in mesopic condition. In high myopia correction, femto-LASIK and PRK have better results in photopic and SMILE in mesopic condition.

Comparison of corneal aberrations and refractive outcomes after small-incision lenticule extraction and femtosecond-assisted laser-assisted in situ keratomileusis

PURPOSES

To retrospectively compare the short-term refractive outcomes and corneal aberrations after small-incision lenticule extraction (SMILE) and femtosecond-assisted laser-assisted in situ keratomileusis (FS-LASIK) combined with smart pulse technology (SPT) in patients with compound myopic astigmatism.

METHODS

A total of 91 eyes (91 patients) were included, 43eyes in FS-LASIK group and 48 eyes in the SMILE group. Uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), refractive results and corneal topography were evaluated 1 and 3 months postoperatively. Corneal aberrations of anterior corneal surface were calculated from the topography data over 6 mm-diameter.

RESULTS

There was no significant difference in UCVA, BCVA, and refractive results between the two groups. There were no statistical difference in TIA (target induced astigmatism), SIA (surgery induced astigmatism), DV (difference vector), ME (magnitude of error), AE (angle of error), AE (absolute value) and CI (correction index) between both groups at 1 and 3 months. Coma and spherical aberration improved in all the patients in both groups at 1 and 3 months postoperatively. The amount of induced spherical aberrations was higher in FS-LASIK group compared to SMILE group.

CONCLUSIONS

Both FS-LASIK and SMILE achieved similar refractive outcomes in patients with myopia and compound myopic astigmatism. FS-LASIK combined with SPT resulted in higher spherical aberration than SMILE in early postoperative period.

Comparison of early visual outcomes after low-energy SMILE, high-energy SMILE, and LASIK for myopia and myopic astigmatism in the United States

PURPOSE

To compare uncorrected distance visual acuities (UDVAs) and induced higher-order aberrations (HOAs) in the early postoperative period between low-energy (LE) small-incision lenticule extraction (SMILE), high-energy (HE) SMILE, and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) procedures.

SETTING

University based refractive surgery center.

STUDY DESIGN

Retrospective cohort study.

METHODS

Records of patients who underwent SMILE or FS-LASIK were retrospectively reviewed. SMILE patients were separated into 2 groups: HE settings (125 nJ, 3.0 μm spot spacing) and LE settings (125-130 nJ, 4.5 μm spot spacing). UDVA was measured at postoperative day (POD) 1. Corneal HOAs and UDVA were measured at postoperative month (POM) 1. Induced spherical aberration, vertical coma, horizontal coma, total coma, and total HOAs were calculated.

RESULTS

The study included 147 eyes of 106 patients, 49 in each group. For SMILE patients, the difference in mean UDVA at POD1 was highly statistically significant in favor of the LE group (-0.003 vs 0.141, P < .0001). No significant difference in mean UDVA at POD1 was noted between the LE group and FS-LASIK group (-0.003 vs -0.011, P = .498). Induced change in spherical aberration was less in LE SMILE than that in FS-LASIK (0.136 vs 0.186 μm, P = .02) at POM1. No significant differences in POM1 mean UDVA (-0.033 vs -0.036) or induced change in all other HOAs were noted between LE SMILE and FS-LASIK.

CONCLUSIONS

LE settings were associated with significantly improved POD1 UDVA. POD1 and POM1 UDVA were comparable with those of FS-LASIK. Spherical aberration induction was less with LE SMILE than that with FS-LASIK, whereas all other induced HOAs were comparable with FS-LASIK.

Preliminary results of a new intrastromal corneal ring segment as a tissue saving procedure in photorefractive keratectomy to correct moderate to high myopia

AIM

To evaluate the clinical results after implantation of a new intrastromal corneal ring segment (ICRS) associated with photorefractive keratectomy (PRK) to correct high myopia (HM) patients with thin corneas.

METHODS

We evaluated 42 eyes of 23 HM patients that had ICRS implantation followed by PRK. The mean age of patients was 29.1±7.12y (range 18 to 40 years old). Uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), keratometry, spherical equivalent, pachymetry, and aberrometry were compared using ANOVA with repeated measurements evaluated preoperatively and at last follow-up visit after the procedures. The refractive predictability and simulated/real corneal ablation were also assessed.

RESULTS

The mean follow-up time after PRK was 6.8±1.6mo. The mean preoperative UCVA improved from 20/800 preoperative to 20/100 after ICRS and 20/35 after PRK. The mean preoperative BCVA was 20/25 (range from 20/30 to 20/20) and remained unchanged after ICRS implantation. Following the PRK the mean BCVA was 20/25 (range from 20/30 to 20/20). The mean spherical equivalent decreased from -7.25±1.12 (range -5.00 to -9.00) preoperatively to -3.32±1.0 (range -2.00 to -5.00) postoperatively (P<0.001) after ICRS implantation and decreased from -2.44±1.51 preoperatively to 0.32±0.45 (range -0.625 to 0.875) postoperatively (P<0.001) after PRK. The change in BCVA and topographic astigmatism was statistically significant (P<0.0001).

CONCLUSION

ICRS in HM associated with PRK can be a tissue saving procedure and an alternative surgical option for correction of moderate to high myopia.

Comparison of refractive outcomes and high-order aberrations after small incision lenticule extraction and wavefront-guided femtosecond-assisted laser in situ keratomileusis for correcting high myopia and myopic astigmatism

PURPOSE

To compare the results of using small incision lenticule extraction (SMILE) and wavefront-guided femtosecond-assisted laser in situ keratomileusis (WFG FS-LASIK) to correct high myopia and myopic astigmatism.

MATERIAL AND METHODS

The 94 eyes of 47 patients with high myopia or myopic astigmatism, if not both, who had undergone SMILE were compared with the 94 eyes of 47 patients with high myopia or myopic astigmatism, also if not both, who had undergone WFG FS-LASIK. Only eyes with high myopic or myopic astigmatism errors greater than - 6.0 diopter (D) spherical refraction and 0-3 D cylindrical refraction were included. Values of uncorrected distance visual acuity, corrected distance visual acuity, efficacy index, safety index, predictability, and high-order aberration between the patient groups were compared.

RESULTS

The SMILE and WFG FS-LASIK groups did not significantly differ according to sex or age. Values of preoperative and postoperative spherical refraction, cylindrical refraction, spherical equivalent, uncorrected distance visual acuity, and corrected distance visual acuity between the groups also did not significantly differ nor did values of predictability, the efficacy index, or the safety index. SMILE induced more coma and trefoil (p < 0.001), whereas WFG FS-LASIK induced more spherical aberration (p < 0.001).

CONCLUSION

Both SMILE and WFG FS-LASIK are efficient, safe, predictable procedures for correcting high myopia and myopic astigmatism. SMILE may induce more coma and trefoil, whereas WFG FS-LASIK may induce more spherical aberration.

Prospective, Randomized, Contralateral Eye Comparison of Wavefront-Guided and Wavefront-Optimized Laser in Situ Keratomileusis

PURPOSE

To compare outcomes in wavefront-optimized (WFO) laser in situ keratomileusis (LASIK) to high-resolution wavefront-guided (WFG) LASIK.

DESIGN

Randomized, fellow eye controlled, clinical trial.

METHODS

A total of 200 eyes of 100 patients with myopia or compound myopic astigmatism undergoing bilateral LASIK between October 2015 and February 2017 underwent wavefront-optimized (WFO) LASIK in 1 eye and wavefront-guided (WFG) LASIK in the fellow eye. Each eye was evaluated for uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), contrast sensitivity, refractive error, and wavefront aberrometry. Outcome measurement primarily UDVA at 12 months. Secondary outcomes were safety, predictability, stability, refractive error, CDVA, contrast sensitivity, and higher-order aberrations at 12 months.

RESULTS

WFG LASIK had higher levels of supervision and better contrast sensitivity compared to WFO. Both types had excellent postoperative UDVA results, without a significant difference in either mean UDVA or frequency of achieving a specified UDVA, for example, 20/16 or better (all P > 0.05). The mean gain in lines of CDVA was significantly higher in the WFG than in the WFO group (0.80 ± 0.75 vs 0.62 ± 0.72, respectively; P = 0.04). The WFG cohort had significantly better contrast sensitivity for mean and frequency of achieving >20/40 for <5% low-contrast sensitivity (37.1%; 95% confidence interval [CI], 27.5-46.7 vs 24.7%; 95% CI, 16.2-33.3, respectively; P = 0.01) and >20/32 for <25% low-contrast sensitivity (10.3%; 95% CI, 4.3-16.4 vs 4%, respectively; 95% CI, 0.0-8.1, respectively; P = 0.04). The WFO group had a significantly higher frequency of <0.25 diopters (D) of refractive astigmatism at 12 months (82.5%; 95% CI, 75.0-90.0; vs 72.1%, respectively; 95% CI, 63.2-81.2; P = 0.02) but not <0.50 D (95.6%; 95% CI, 91.9-99.8; vs 96.9, respectively; 95% CI, 93.5-100; P = 0.61). The WFG group was significantly closer to emmetropia for both sphere and spherical equivalents at all time points. Trefoil was significantly lower in the WFG group and was also significantly lower than preoperative measurements.

CONCLUSIONS

Wavefront-optimized and high-resolution wavefront-guided LASIK achieve excellent visual outcomes. Nonetheless, treatments based on a high-resolution aberrometer appear to offer superior results in some regards.

Comparison of Visual, Refractive and Ocular Surface Outcomes Between Small Incision Lenticule Extraction and Laser-Assisted In Situ Keratomileusis for Myopia and Myopic Astigmatism

Laser-assisted in situ keratomileusis (LASIK) is the most commonly performed laser refractive surgical technique worldwide for the treatment of myopia and myopic astigmatism. In recent years, small incision lenticule extraction (SMILE) has emerged as a promising alternative to LASIK, requiring only a single femtosecond laser to create an intrastromal lenticule, which is then removed via a small incision. The technique obviates the need for a corneal flap. A number of published studies have compared the two techniques in terms of visual, refractive and ocular surface outcomes. This review compares the clinical outcomes between LASIK and SMILE in treating myopia and myopic astigmatism based on studies published in the last 5 years. Twenty-two studies were included, all of which were observational in nature. Results suggest that the two techniques have comparable visual outcomes in terms of safety, efficacy and predictability, although recovery in visual acuity may be slower in SMILE-treated than LASIK-treated eyes. SMILE is found to result in less severe postoperative dry eye symptoms and faster recovery of corneal sensitivity than LASIK. It is important to note, however, that the SMILE technique is limited by the lack of a cyclotorsion-compensation system and option for customized treatment profile. The heterogeneity of results in this review may be attributable to the use of different LASIK platforms in different studies. Few studies compared the outcomes regarding severity of myopia. Future prospective randomized controlled trials with a larger sample size and longer follow-up period will be highly beneficial for progress in this field.

Comparing Patient-Reported Outcomes of Laser In Situ Keratomileusis and Small-Incision Lenticule Extraction: A Review

PURPOSE

Laser in situ keratomileusis (LASIK) and small-incision lenticule extraction (SMILE) are popular refractive surgeries. The objective refractive outcomes of LASIK and SMILE have been studied extensively; both procedures have comparable safety, efficacy, and predictability. However, owing to various psychosocial factors, refractive patients may report dissatisfaction despite good postoperative vision. Hence the importance of studies on subjective patient-reported outcomes. This review discusses the role of psychometric-technique-based validated questionnaires when evaluating subjective outcomes. It also summarizes the literature on patient-reported outcomes for LASIK and SMILE.

DESIGN

A literature search was performed on PubMed database to identify studies that have assessed patient-reported outcomes for LASIK and SMILE.

RESULTS

Several studies have looked into patient-reported outcome measures for LASIK, but the number of equivalent studies for SMILE is limited. Questionnaires (validated and non-validated) are used to evaluate patient-reported outcomes. Validated questionnaires are designed based on psychometric techniques, such as Classic Test Theory, Item Response Theory, and Rasch analysis. The Quality of Life Impact of Refractive Correction (QIRC) questionnaire, a validated questionnaire administered to both LASIK and SMILE patients, suggests that both groups have comparable vision-related quality of life in the first few months postoperatively; but SMILE might confer a slight advantage in the later postoperative period (postoperative month 6).

CONCLUSIONS

Future LASIK-SMILE comparative studies utilizing standardized validated questionnaires for patient-reported outcome measures with longer follow-up durations would be a welcome contribution to this important aspect of refractive surgery.

Comparison of higher order wavefront aberrations with four aberrometers

Purpose:

To evaluate the agreement of selected higher order aberration measurements between aberrometers based on three different wavefront technologies.

Methods:

Twenty-three eyes of 23 participants were compared between Zywave, OPD-Scan III, and iDesign aberrometers, for total ocular aberrations. Participants were between 19 and 69 years of age, and exclusion criteria were previous ocular surgery or trauma, contact lens wear within the preceding 2 weeks, and ocular or systemic disease. Corneal aberrations were compared between the OPD-Scan III and GALILEI™ G2 aberrometers. Zernike coefficients of vertical and oblique trefoil, vertical and horizontal coma, and spherical aberration were analyzed in R software.

Results:

In all, 276 scans were captured in total, with a male-to-female ratio of 11:12. Total ocular vertical coma [mean difference (MD) = 0.026 μm, P < 0.005], vertical trefoil (MD = 0.033 μm, P < 0.05), and spherical aberration (MD = 0.022 μm, P < 0.05) differed significantly between the iDesign and OPD-Scan III. Differences in total vertical (MD = 0.072 μm, P < 0.05) and oblique trefoil (MD = 0.058 μm, P < 0.05) were demonstrated between the Zywave and OPD-Scan III, and spherical aberration (MD = 0.030 μm, P < 0.005) between iDesign and Zywave. iDesign corneal horizontal coma (MD = 0.025 μm, P < 0.05) and spherical aberration (MD = 0.043 μm, P < 0.005) measurements were significantly different between the GALILEI™ G2 and the OPD-Scan III.

Conclusion:

Zywave, iDesign, and OPD-Scan III, and GALILEI™ G2 and OPD-Scan III may be used interchangeably for their total ocular and corneal wavefront functions, respectively; however, care must be taken if using these devices for guiding ablation or monitoring corneal disease.

Quality of life after refractive surgery: ReLEx SMILE vs Femto-LASIK

Purpose

The safety and effectiveness of complex myopic astigmatism correction using ReLEx SMILE or Femto-LASIK techniques have been well established. The purpose of the current study is to compare quality of life (QoL) outcomes following ReLEx SMILE or Femto-LASIK procedures in parallel with functional vision and anatomic outcomes of treated eyes.

Patients and methods

This prospective, consecutive series included 118 patients, 18–43 years of age, out of which 56 underwent ReLEx SMILE and 62 underwent Femto-LASIK surgery for correction of myopic astigmatism. All patients underwent standard comprehensive ophthalmic examinations, and additionally, completed The Quality of Life Impact of Refractive Correction Questionnaire to determine the impact the vision-correction treatment had on their QoL.

Results

In both treatment groups, the postoperative refractive outcomes were comparable, with visual acuity improvements for both groups noted the day following surgery. After laser correction of complex myopic astigmatism using Femto-LASIK and ReLEx SMILE methods, the overall QoL indicators are statistically significant (P<0.01) exceeding preoperative values 1 month after the operation and reaching the maximum values by the end of the observation period (P<0.0001).

Conclusion

The results of the study suggest that patients require some time to adapt to their new visual function and its impact on their daily living, delaying detectable improvements in QoL. Moreover, these results may suggest a higher satisfaction trend and long-term QoL in patients undergoing ReLEx SMILE in comparison to Femto-LASIK. Long-term results from the study demonstrated high patient satisfaction with both methods.

Corneal higher-order aberrations of the anterior surface, posterior surface, and total cornea after small incision lenticule extraction (SMILE): high myopia versus mild to moderate myopia

Background

To investigate corneal higher-order aberrations (HOAs) of the anterior surface, posterior surface, and total cornea after small incision lenticule extraction (SMILE) in high myopic and mild to moderate myopic patients.

Methods

This retrospective study included 197 eyes (101 patients) undergoing SMILE surgery. According to the preoperative spherical equivalent (SE), treated eyes were divided into two groups: a high myopic group (more than − 6.0 D, Group H) and a mild to moderate myopic group (less than − 6.0 D, Group M). Corneal HOAs of the anterior surface, posterior surface, and total cornea were measured using a Scheimpflug camera preoperatively and 3 months postoperatively. Pearson’s correlation analysis was conducted to determine relationships between corneal aberrations and the SE.

Results

There were no significant differences in third-order to eight-order aberrations (RMS HOAs) of the anterior surface, posterior surface, and total corneal between the two groups before SMILE surgery. However, after SMILE, anterior and total corneal HOAs, especially vertical coma and spherical aberrations, significantly increased in both groups (p < 0.0167), whereas posterior corneal HOAs remained relatively stable (p > 0.0167). The induction of HOAs was significantly greater in Group H than Group M postoperatively (p < 0.0167). Changes in anterior surface and total corneal HOAs, especially vertical coma and spherical aberrations, were related to the SE (p < 0.05).

Conclusions

Anterior and total corneal HOAs, particularly vertical coma and spherical aberrations, significantly increased after SMILE in both groups, whereas posterior corneal HOAs remained stable. Aberration changes were related to SE.

Trial registration

Retrospectively registered. ChiCTR-ORC-17011040. Registered 1 April 2017. Name of registry: The observation of clinical results after corneal refractive surgery. Data of enrolment of the first participant to the trial: 15 December 2016.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

WFG LASIK and SMILE had similar aberrometric outcomes but WFG LASIK had better postoperative visual acuity. Surgeon experience, internal aberrations, small pupil size, and wound healing can enable similar outcomes in both procedures. [J Refract Surg. 2018;34(8):527-532.].

Three-year outcomes of small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) for myopia and myopic astigmatism

Aims

To compare long-term clinical outcomes following small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) for myopia and myopic astigmatism correction.

Methods

In this retrospective study, we enrolled a total of 101 patients (101 eyes) who underwent SMILE or FS-LASIK 3 years prior. Measured parameters included uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction and corneal wavefront aberrations.

Results

No significant differences in patient characteristics were found between the two groups. At the 3-year follow-up, UDVA was better than or equal to 20/20 in 90% and 85% (p=0.540) of the eyes; the efficacy indexes were 1.05±0.19 and 1.01±0.21 in the SMILE and FS-LASIK groups, respectively (p=0.352). Safety indexes were 1.19±0.17 and 1.15±0.20 in the SMILE and FS-LASIK groups, respectively (p=0.307). Eighty per cent and 65% of eyes were within ±0.50 D of the attempted spherical equivalent correction after SMILE and FS-LASIK, respectively (p=0.164). Vector analysis revealed no significant differences in astigmatic correction between the two groups (p>0.05). Surgically induced spherical aberration was higher in the FS-LASIK group than in the SMILE group (p<0.001).

Conclusion

Long-term follow-up analysis suggested that both SMILE and FS-LASIK were safe and equally effective for myopic and astigmatic correction.

Recent advances in wavefront-guided LASIK

PURPOSE OF REVIEW

Laser vision correction remains an active area of research, and there have been many recent advances in the field. The purpose of this review is to provide an update on the recent advances for one of the most common methods of laser vision correction, wavefront-guided laser in-situ keratomileusis (LASIK).

RECENT FINDINGS

Recent technological advancements in wavefront aberrometry are largely responsible for the improved visual outcomes that have been recently reported. In addition, improvements in femtosecond and excimer laser technology, used in flap creation and corneal ablation, have been shown to provide superior results when compared to microkeratomes and earlier lasers. Wavefront-guided LASIK appears to have advantages over some other keratorefractive modalities in terms of visual acuity, predictability, astigmatism correction, and subjective visual symptoms. Nonetheless, there may be some limitations in highly aberrated corneas, and also in biomechanical stability relative to other available platforms.

SUMMARY

Improvements in wavefront aberrometry, and also femtosecond and excimer lasers, have continued to improve our ability to correct refractive errors. Wavefront-guided LASIK remains a well tolerated and effective keratorefractive procedure, with a trend toward superiority. Nonetheless, further studies comparing this modality to others are needed to define the role each can serve.

Visual Outcomes and Higher Order Aberrations Following LASIK on Eyes with Low Myopia and Astigmatism

Background:

Laser-Assisted in situ Keratomileusis (LASIK) can induce corneal aberrations that can impact vision and patient satisfaction. Recent developments in laser technologies have helped minimise these aberrations.

Objective:

To assess the quality of vision and change in Higher-Order Aberrations (HOAs) following wavefront-optimized LASIK in low-myopic astigmatic patients.

Methods:

LASIK was performed on a total of 76 eyes in patients with myopia <4.0 D and cylinder <2.0 D using the WaveLight® EX500 excimer and FS200 femtosecond laser platform. Visual acuity, contrast sensitivity and HOAs were measured at 1 and 3 months postoperatively and compared to preoperative values. Subjective quality of vision was assessed pre- and postoperatively using a VF14 questionnaire.

Results:

Mean postoperative Spherical Equivalent (SE) was -0.09 ± 0.26 µm with 95% of patients within ± 0.5 D of attempted SE. Postoperative uncorrected distance visual acuity was 20/20 or better for 96% of patients. Contrast sensitivity increased against horizontal and vertical gratings at all spatial frequencies except for vertical gratings at 18 cycles/degree. Spherical aberration and total HOA increased by 0.085 µm and 0.13 µm respectively. The mean VF14 score increased from 89.2 ± 16.7% to 99 ± 1.4% postoperatively.

Conclusion:

LASIK performed using the WaveLight® EX500 excimer and WaveLight® FS200 laser platform provided improved contrast sensitivity and visual acuity with minimal introduction of HOAs, making it a suitable platform for low myopic astigmatic patients.

Effect of Cap-Lenticule Diameter Difference on the Visual Outcome and Higher-Order Aberrations in SMILE: 0.4 mm versus 1.0 mm

Purpose

To evaluate the effect of cap-lenticule diameter difference (CLDD) on the visual outcome and higher-order aberrations (HOAs) of small-incision lenticule extraction (SMILE).

Methods

A total of 132 patients who had bilateral SMILE for myopia or myopic astigmatism were included. The CLDD was 0.4 mm in 54 patients (group 1) and 1.0 mm in 78 patients (group 2). The refractive parameters, uncorrected (UDVA) and corrected distance visual acuity (CDVA), and HOAs were determined preoperatively and during six months follow-up.

Results

Group 1 had better CDVA (in logMAR) compared to group 2 at day 1 (−0.07 ± 0.07 versus 0.04 ± 0.07, resp.; p < 0.001) and week 1 (−0.07 ± 0.07 versus –0.04 ± 0.07, resp.; p = 0.001). The visual acuity improved more in group 1 than in group 2. The UDVA (in logMAR) was 0.07 ± 0.07 and 0.29 ± 0.09 at day 1 (p < 0.001) and −0.08 ± 0.07 and −0.06 ± 0.06 at six months (p = 0.038) in group 1 and group 2, respectively. Group 1 was associated with significantly less induction of HOAs (0.24 ± 0.08 μm and 0.32 ± 0.26 μm, resp.; p = 0.002).

Conclusions

In SMILE, 0.4 mm CLDD is associated with better visual outcome and less induction of HOAs than 1.0 mm. Narrow CLDD should be considered in SMILE to increase the visual acuity particularly in the early postoperative period.

Comparison of visual results and higher-order aberrations after small incision lenticule extraction (SMILE): high myopia vs. mild to moderate myopia

Background

To compare the refractive results and higher-order aberrations (HOAs) after small incision lenticule extraction (SMILE) in high myopia and mild to moderate myopia patients.

Methods

This prospective study included 165 eyes (86 patients) undergoing SMILE. According to the preoperative spherical equivalent (SE), treated eyes were divided into two groups: the high myopia group (more than -6.0 D, group-H) and the mild to moderate group (less than -6.0 D, group-M). Follow-up intervals were at 1 day, 10 days, 1 month and 3 months postoperatively. We obtained the following parameters: uncorrected (UDVA) and corrected distance visual acuity (CDVA), SE, efficacy and safety index, and HOAs.

Results

Preoperative SE was -7.16 ± 0.93 D in group-H and -4.34 ± 0.97 D in group-M. At 3 months postoperatively, the SE in group-H and group-M was -0.20 ± 0.37 D and 0.01 ± 0.19 D (t = - 4.11, P<0.05), respectively. It was found that 77% and 98% had an UDVA of 20/20, 98% and 99% had a CDVA of 20/20 in group-H and group-M, respectively, while 87% and 95% had a SE within ±0.5 D and ±1.0 D in group-H, and 98% and 100% in group-M. The efficacy indexes were 0.98 ± 0.18 in group-H and 1.05 ± 0.10 in group-M (t = - 3.084, p < 0.05). The safety indexes were 1.06 ± 0.09 and 1.06 ± 0.09 (t = 0.153, p > 0.05), respectively. There were significant increases in total HOAs, 3^rd-order coma, and 4^th-order spherical aberrations.

Conclusions

SMILE is an effective and safe surgery for correcting myopia. But the target correction amount in high myopia patients should be adjusted to avoid undercorrection and acquired more satisfaction. SMILE induced increases of HOAs.

Trial registration

ChiTrial registration number: ChiCTR-OON-16009164. Retrospectively registered: 06.September.2016