Astigmatism Correction Using SMILE

The Risk Factors for Myopia Undercorrection in Second-Generation (Visumax 800) Keratorefractive Lenticule Extraction Surgery: A Retrospective Case-Control Study

In this study, we aim to evaluate the risk factors of myopia undercorrection in recipients of second-generation keratorefractive lenticule extraction (KLEx) surgery. A retrospective case-control study was performed, and patients who received second-generation KLEx surgery were enrolled. The cases with myopia undercorrection were matched to non-myopia undercorrection cases with a 1:4 ratio according to age, and a total of 22 and 88 eyes were categorized into the undercorrection and control groups, respectively. Demographic, refractive, topographic, and surgical data were collected preoperatively. A generalized linear model was operated to evaluate the potential risk factors for myopia undercorrection. The uncorrected distance visual acuity (UDVA) at three months postoperation was significantly better in the control group (p = 0.006), and residual myopia and SE were significantly higher in the undercorrection group during the whole follow-up period (all p < 0.001). The UDVA value showed a trend of improvement in the control group (p < 0.001), and the changes to SE and residual myopia were significantly lower in the control group (both p < 0.001). Regarding the risk factors for myopia undercorrection in the whole population and the high-myopia population, a higher manifest sphere power, higher steep keratometry (K), higher topographic cylinder, lower central corneal thickness (CCT) at apex, higher CCT difference and lower residual stromal thickness (RST) correlated to myopia undercorrection (all p < 0.05). In the low-myopia population, only higher myopia and lower RST correlated to myopia undercorrection (both p < 0.05). In conclusion, a high-sphere power and irregular topographic pattern correlated to myopia undercorrection after the second KLEx surgery, especially for individuals with high myopia.

Correction of High Astigmatism by Autologous Astigmatic Lenticule Reshaping and Rotation

PURPOSE

To explore the use of autologous astigmatic lenticule reshaping and rotation surgery to correct high astigmatism in conjunction with excimer laser technology to correct residual refractive error.

METHODS

Six patients with high astigmatism (8 eyes, all with astigmatism from -5.50 to -11.00 diopters [D]) seeking refractive error correction were enrolled. The following methods were used to correct refractive errors that could not be corrected by a single conventional surgery: (1) cutting of a customized lens using FLEx technology, (2) lifting of the corneal flap and reshaping the autologous astigmatic lenticule in situ using an excimer laser, and (3) rotation of the autologous astigmatic lenticule by 90°. Uncorrected distance visual acuity, subjective refraction, corneal topography, and anterior segment optical coherence tomography were performed preoperatively and postoperatively.

RESULTS

The efficacy and safety indices at 6 months postoperatively were 0.93 ± 0.18 and 1.06 ± 0.11, respectively, the spherical equivalent remained stable and close to emmetropia (-0.13 ± 0.70 D) from 1 to 6 months postoperatively, postoperative astigmatism was generally mildly undercorrected (-1.22 ± 0.43 D), and the difference in corneal curvatures at 2 mm from the apex of the cornea was significantly reduced compared to preoperatively (P < .05); however, the corresponding values at 1 and 3 mm showed no difference.

CONCLUSIONS

Correction of high astigmatism with autologous astigmatic lenticule reshaping and rotation surgery is tissue-sparing, predictable, and significantly improves postoperative visual acuity and quality. This method is feasible and safe, with predictability requiring further study. This novel surgical approach has potential for patients with high astigmatism that cannot be corrected by conventional refractive surgery. [J Refract Surg. 2024;40(8):e554-e561.].

Epithelial Remodeling and Epithelial Wavefront Aberrometry after Spherical vs. Cylindrical Myopic Small Incision Lenticule Extraction (SMILE)

Background/Objectives: To compare the epithelial thickness changes and the changes in epithelial wavefront aberrometry following spherical versus astigmatic myopic small incision lenticule extraction (SMILE). Methods: Eighty-six eyes of 86 patients who underwent SMILE were included in this retrospective study. A total of 43 eyes underwent myopic spherical correction (spherical group) and 43 eyes underwent myopic cylindrical correction (cylindrical group). The groups were matched according to the spherical equivalent of surgically corrected refraction. Subjective manifest refraction as well as high-resolution anterior segment optical coherence tomography (MS-39; CSO; Florence, Italy) were obtained preoperatively as well as 3 months postoperatively. The latter was utilized for computing epithelial wavefront aberrometry in addition to epithelial thickness mapping. Results: Epithelial thickness increased significantly in both groups after SMILE (p < 0.01). In the cylindrical group, epithelial thickening was more pronounced on the flat meridian compared to the steep meridian (p = 0.04). In both groups, epithelial wavefront aberrometry showed a significant postoperative increase in the epithelium's spherical refractive power, causing a myopization of -0.24 ± 0.42 diopters (D) in the spherical group (p < 0.01) and -0.41 ± 0.52 D in the cylindrical group (p < 0.0001). While no significant changes in epithelial cylindrical refractive power were observed in the spherical group, a significant increase was noted in the cylindrical group from -0.21 ± 0.24 D to -0.37 ± 0.31 D (p = 0.01). In both groups, epithelial higher-order aberrations increased significantly (p < 0.001). Conclusions: Postoperative epithelial remodeling after SMILE alters lower-order (sphere and cylinder) and higher-order aberrations of the corneal epithelial wavefront and might contribute to refractive undercorrection, especially in astigmatic corrections. Epithelial wavefront aberrometry can be used to quantify the refractive effect of epithelial remodeling processes after keratorefractive surgery.

The Efficiency, Predictability, and Safety of First-Generation (Visumax 500) and Second-Generation (Visumax 800) Keratorefractive Lenticule Extraction Surgeries: Real-World Experiences

We aimed to evaluate the postoperative visual and refractive outcomes between the first- and second-generation keratorefractive lenticule extraction (KLEx) surgeries. A retrospective cohort study was conducted and patients who had received first- and second-generation KLEx surgeries were enrolled. A total of 80 and 80 eyes were categorized into the first and second KLEx groups after exclusion, respectively. The primary outcomes were the postoperative uncorrected distance visual acuity (UDVA), spherical equivalent (SE), and safety indexes. An independent t-test and generalized estimate equation were implemented to compare the primary outcomes between the two groups. After the KLEx surgery, the UDVA showed no significant difference between the two groups throughout the study period (all p > 0.05), and the postoperative SE and safety index were also statistically identical between the two groups during the follow-up interval (all p > 0.05). There was a similar trend of visual recovery between the two groups (aOR: 0.967; 95% CI: 0.892-1.143; p = 0.844), while the amplitude of the SE change was significantly lower in the second KLEx group (aOR: 0.760; 95% CI: 0.615-0.837; p = 0.005). Nine and two unintended initial dissection of the posterior plane (UIDPP) occurred intraoperatively in the first and second KLEx groups, respectively, and the second group showed a lower risk of UIDPP (p = 0.032). In conclusion, the efficiency, predictability, and safety are similar between first- and second-generation KLEx surgeries.

Topographic and Surgical Risk Factors for Early Myopic Regression between Small Incision Lenticule Extraction and Laser In Situ Keratomileusis

Our objective was to evaluate the topographic and surgical factors of early myopic regression between laser in situ keratomileusis (LASIK) and small-incision lenticule extraction (SMILE). A retrospective case-control study was conducted, and 368 and 92 eyes were enrolled in the LASIK and SMILE groups via propensity score matching (PSM). Visual acuity, refractive status, axial length, and topographic/surgical parameters were collected. Multiple linear regression was applied to the yield coefficient and the 95% confidence interval (CI) of the parameters. The cumulative incidence of early myopic regression was higher in the LASIK group (p < 0.001). In the SMILE group, a lower central corneal thickness (CCT) thinnest value and a higher corneal cylinder associated with early myopic regression were observed; meanwhile, in the LASIK group, a lower CCT thinnest value, a higher steep corneal curvature, a larger optic zone, and a lower flap thickness related to early myopic regression were observed (all p < 0.05). In the SMILE group, a higher CCT difference correlated with early myopic regression was observed compared to the LASIK group (p = 0.030), and higher steep corneal curvature and lower cap/flap thickness (both p < 0.05) correlated with early myopic regression were observed in the LASIK group compared to the SMILE group. In conclusion, CCT differences significantly influence early myopic regression in the SMILE group; meanwhile, corneal curvature and flap thickness affect early myopic regression principally in the LASIK group.

Effective optical zone following small incision lenticule extraction: a review

Small incision lenticule extraction (SMILE) is a "flapless" keratorefractive surgery with excellent safety, efficacy, stability, and predictability for myopia correction. A recent global multicenter study also reported good refractive outcomes for hyperopic SMILE. SMILE has shown advantages including improved biomechanical strength, fewer dry eye symptoms, less corneal denervation, and fewer surgery-induced higher-order aberrations over laser in situ keratomileusis (LASIK). However, night vision complaints, including glare, halos, and starbursts, could still occur after SMILE. These symptoms have been proven to be closely related to the effective optical zone (EOZ), which is defined as the achieved area of corneal ablation. A larger postoperative EOZ may indicate better visual quality, making EOZ an important safety parameter for keratorefractive surgeries. As SMILE has gained wider application globally, the EOZ following SMILE has also been increasingly studied in the field of refractive surgery. This review provides an update on topics related to the EOZ after SMILE, including its measurement and influencing factors, aiming to benefit the personalization of the surgical algorithm and ultimately improve the visual quality after the SMILE procedure.

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.

Effect of Cyclotorsion Compensation in Small Incision Lenticule Extraction Surgery for the Correction of Myopic Astigmatism: A Systematic Review and Meta-Analysis

INTRODUCTION

Small incision lenticule extraction (SMILE) has made notable advancements in addressing myopic astigmatism. Nevertheless, the potential impact of cyclotorsion on surgical outcomes cannot be overlooked. This study aims to assess the effectiveness of cyclotorsion compensation technology in SMILE surgery for the correction of myopic astigmatism, examining its influence on postoperative visual quality.

METHODS

A systematic review and meta-analysis were conducted. A comprehensive literature search was performed using databases, including PubMed, Web of Science, EMBASE, Cochrane Library, EBSCO, Scopus, CNKI, VIP, and Wan Fang. Studies meeting the criteria were selected and included. Data were independently extracted by three authors. Clinical outcome parameters were analyzed using Review Manager version 5.3.

RESULTS

This meta-analysis included ten studies. The results showed that, compared with the control group (cyclotorsion compensation was not performed in SMILE), the following indicators in the cyclotorsion compensation group were: residual astigmatism (RA) [weighted mean difference (MD) = 0.73, 95% confidence interval (CI) + 0.26 to + 1.19, P = 0.002], spherical equivalent (SE) (MD = 1.99, 95% CI + 0.77 to + 3.21, P = 0.001), coma (MD = -0.06, 95% CI -0.08 to -0.04, P < 0.00001), higher-order aberrations (HOAs) (MD = -0.04, 95% CI -0.06 to -0.02, P < 0.0001), follow-up 6-month angle of error (AE) (MD = -2.67, 95% CI -3.71 to -1.63, P < 0.00001), and follow-up 6-month uncorrected distance visual acuity (UDVA) (MD = -0.05, 95% CI -0.08 to -0.01, P = 0.005), and the differences in results were statistically significant. However, the differences among correction index, index of success (IOS), targeted induced astigmatism (TIA), magnitude of error (ME), and spherical aberration (SA) were not statistically significant.

CONCLUSION

Cyclotorsion compensation proves to be effective and predictable for correcting myopic astigmatism. The cyclotorsion compensation group demonstrated advantages over the control group in terms of postoperative residual astigmatism, and it induced fewer coma aberrations. Whether cyclotorsion compensation can lead to better visual quality remains to be seen, and further research on correcting myopic astigmatism through cyclotorsion compensation is warranted.

Choice of refractive surgery types for myopia assisted by machine learning based on doctors' surgical selection data

In recent years, corneal refractive surgery has been widely used in clinics as an effective means to restore vision and improve the quality of life. When choosing myopia-refractive surgery, it is necessary to comprehensively consider the differences in equipment and technology as well as the specificity of individual patients, which heavily depend on the experience of ophthalmologists. In our study, we took advantage of machine learning to learn about the experience of ophthalmologists in decision-making and assist them in the choice of corneal refractive surgery in a new case. Our study was based on the clinical data of 7,081 patients who underwent corneal refractive surgery between 2000 and 2017 at the Department of Ophthalmology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences. Due to the long data period, there were data losses and errors in this dataset. First, we cleaned the data and deleted the samples of key data loss. Then, patients were divided into three groups according to the type of surgery, after which we used SMOTE technology to eliminate imbalance between groups. Six statistical machine learning models, including NBM, RF, AdaBoost, XGBoost, BP neural network, and DBN were selected, and a ten-fold cross-validation and grid search were used to determine the optimal hyperparameters for better performance. When tested on the dataset, the multi-class RF model showed the best performance, with agreement with ophthalmologist decisions as high as 0.8775 and Macro F1 as high as 0.8019. Furthermore, the results of the feature importance analysis based on the SHAP technique were consistent with an ophthalmologist's practical experience. Our research will assist ophthalmologists in choosing appropriate types of refractive surgery and will have beneficial clinical effects.

Impact of the preoperative cylinder on astigmatism correction in femtosecond lenticule extraction (FLEX): a prospective observational study

PURPOSE

To explore the impact of the preoperative manifest cylinder on astigmatism correction via femtosecond lenticule extraction (FLEX), or small incision lenticule extraction (SMILE).

METHODS

This was a prospective observational study. Eyes were categorized into mild (n = 88), moderate (n = 46), and severe (n = 53) astigmatism groups, based on the preoperative manifest cylinder. Vector analysis was conducted with the back vertex distance set at 12 mm. The primary outcome was the correction index (CI), with secondary outcomes including the safety, efficacy, predictability, and vectoral alterations related to FLEX.

RESULTS

The average target-induced astigmatism was 0.45 ± 0.20 D, 0.95 ± 0.17 D, and 1.99 ± 0.65 D in the three groups (P < 0.001), and the average CI was 1.12± 0.05, 1.01 ± 0.03, and 0.95 ± 0.02 (P = 0.020), with the severe astigmatism group displaying a notably lower CI. The efficacy, safety, predictability, or stability of FLEX did not demonstrate any significant differences among the three groups. The CIs exhibited a significant difference in eyes with with-the-rule (WTR) astigmatism and against-the-rule (ATR) astigmatism from the mild to severe astigmatism group. In eyes with oblique astigmatism, the average CI exceeded one.

CONCLUSION

Patients with manifest cylinder exceeding 1.25 D have a heightened risk of under-correction in WTR and ATR astigmatism compared to those with mild astigmatism, and mild over-correction may occur in cases of oblique astigmatism.

Comparison of myopic astigmatic correction after cross-assisted SMILE, FS-LASIK, and transPRK

PURPOSE

To compare astigmatic correction among cross-assisted small-incision lenticule extraction (SMILE), femtosecond laser-assisted in situ keratomileusis (FS-LASIK), and transepithelial photorefractive keratectomy (transPRK).

SETTING

The Eye Hospital of Wenzhou Medical University, Zhejiang, China.

DESIGN

Prospective comparison study.

METHODS

154 right eyes of 154 patients with astigmatism of -1.00 to -2.75 diopters (D) were included in this study. 64 eyes, 42 eyes, and 48 eyes were receiving SMILE, FS-LASIK, and transPRK, respectively. The SMILE group used cross-axial alignment for head positioning for astigmatism correction. In the FS-LASIK and transPRK groups, static and dynamic cyclotorsion control were used. Changes in ocular parameters and vector analysis were assessed at 6 months postoperatively.

RESULTS

The safety and efficacy indices were comparable among the 3 groups at 6 months postoperatively. Residual astigmatism was smallest in the SMILE group (-0.23 ± 0.25 D) compared with that in FS-LASIK (-0.40 ± 0.28 D, P = .009) and transPRK groups (-0.42 ± 0.32 D, P = .001). 53 (82.8%), 36 (85.7%), and 37 (77.1%) eyes achieved an angle of error within ±5 degrees, respectively ( P = .55). Notably, vector analysis showed that the difference vector, the magnitude of the error, and its absolute value were significantly smaller in the SMILE group than those in the other groups ( P < .05). In addition, the higher-order aberrations, especially coma, were significantly induced postoperatively in each group ( P < .001).

CONCLUSIONS

Residual astigmatism magnitude was smallest by cross-assisted SMILE, followed by FS-LASIK and transPRK, and the astigmatism axial correction was comparable among groups.

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.

12-Month Outcomes of Small Incision Lenticule Extraction With Proper Head Positioning but No Reference Marking for the Correction of Astigmatism

PURPOSE

To investigate the 12-month outcomes of small incision lenticule extraction (SMILE) with proper head positioning but no reference marking for correcting astigmatism.

METHODS

This was a retrospective cohort study of 3,541 patients (5,953 eyes) who underwent SMILE between July 2010 and April 2021. Patient positioning on the treatment bed was meticulously done in every patient to avoid face turn, head tilt, and chin-up or chin-down posture. The corrected distance visual acuity (CDVA), uncorrected distance visual acuity (UDVA), manifest refraction, astigmatic outcomes, and adverse events were evaluated at 1, 3, and 12 months postoperatively.

RESULTS

The mean preoperative manifest spherical equivalent and manifest cylinder were -5.15 ± 2.24 diopters (D) (range: -0.13 to -12.88 D) and -1.00 ± 0.77 D (range: -0.25 and -6.00 D), respectively. Of all eyes, 88.4% and 98.6% had the spherical equivalent within ±0.50 and ±1.00 D of emmetropia at 12 months. The percentage of eyes with UDVA of 20/20 or better was 92.5%. Six eyes (0.1%) lost two or more lines of CDVA at the 12-month visit. The predictability of cylinder correction was excellent, with 88.1% within ±0.50 D and 98.9% within ± 1.00 D of astigmatism correction at 12 months. The mean correction index (CI) at 12 months was 1.09 ± 0.45 (range: 0.17 to 4.99), indicating a slight astigmatism overcorrection. The high cylinder group tended to have undercorrection with greater residual astigmatism, whereas the low cylinder group was likely to have overcorrection with lesser residual astigmatism (P < .001). No serious adverse events were observed.

CONCLUSIONS

SMILE with proper head positioning but no reference marking produces safe, efficient, predictable, and stable outcomes for astigmatism correction over a 12-month period. [J Refract Surg. 2023;39(10):683-692.].

Influence of Preoperative Parameters on the Ratio of Keratometric Change per Diopter of Attempted Spherical Equivalent (∆K/∆SEQ) for Myopic Correction Within LASIK, PRK, and SMILE

Purpose

To compare 3 of the most common corneal refractive procedures; PRK, LASIK, and SMILE assessing ΔK/ΔSEQ ratio and its correlation with preoperative demographics including age, keratometry, pachymetry, cylinder value, and attempted myopic correction. The goal was to analyze the relative strength of each preoperative parameter in accounting for changes in ∆K/∆SEQ.

Patients and Methods

A total of 370 eyes from 102 male and 97 female patients (173 eyes PRK, 153 LASIK, and 44 SMILE) with ages ranging from 20 to 51 underwent refractive surgery for myopia between -0.25 and -7.71 D manifest refraction spherical equivalent (MRSE). All surgeries were performed at a single surgery center in Draper, Utah. The Pentacam was used for all optical measurements and data were gathered pre-operatively and then again 1-year post-operatively. Only patients who achieved emmetropia at a visual acuity of 20/25 or better were included.

Results

The mean ΔK/ΔSEQ ratio for LASIK (0.839 ± 0.020) was significantly greater than that of PRK (0.775 ± 0.022) and SMILE (0.709 ± 0.046). Age was found to negatively correlate with ΔK/ΔSEQ for both LASIK (r = -0.177) and SMILE (r = -0.451) procedures. Pre-op keratometry was found to negatively correlate with ΔK/ΔSEQ for LASIK (r = -0.202) but not for PRK or SMILE. Pre-op pachymetry was not correlated with ΔK/ΔSEQ for any of the procedures. Attempted myopic spherical equivalent (SEQ) correction was positively correlated with ΔK/ΔSEQ for LASIK (r = 0.236), PRK (r = 0.459), and SMILE (r = 0.304). Lastly, pre-op cylinder value was found to be correlated to ΔK/ΔSEQ in SMILE (r = -0.367), but not in LASIK or PRK.

Conclusion

The ΔK/ΔSEQ ratio not only differs depending on the procedure being done but also by pre-operative factors such as age, keratometry, attempted correction, and cylinder value. Multiple linear regression analysis revealed that the attempted correction had the greatest effect on ∆K/∆SEQ out of all parameters in LASIK and PRK. For SMILE, age had the greatest predictive value of the change in ∆K/∆SEQ. While the exact effect of these parameters will vary by surgeon, all of these should be factored into a refractive surgeon's nomograms in order to achieve optimal visual outcomes for their patients.

Efficacy Comparison Between Toric Posterior Chamber Phakic IOL and Posterior Chamber Phakic IOL Plus Modified Steep Meridian Corneal Relaxing Incision for Moderate to High Astigmatism Corrections

PURPOSE

To compare posterior chamber phakic intraocular lens (Implantable Collamer Lens [STAAR Surgical]) (ICL) plus modified steep meridian corneal relaxing incision (MS-CRI) to toric posterior chamber phakic intraocular lens (Toric Implantable Collamer Lens [STAAR Surgical]) (TICL) implantation for the correction of moderate to high astigmatism.

METHODS

In this prospective, randomized clinical trial, patients with myopia who had moderate to high astigmatism (200 eyes) were enrolled and divided into TICL (n = 100) and MSCRI (n = 100) groups. All patients underwent examinations for uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and subjective refraction before surgery and at the 1- and 6-month follow-up visits. Vector astigmatism analysis was evaluated using the Alpins method.

RESULTS

The mean UDVA and CDVA demonstrated significant improvement after surgery in both groups. During the 6-month follow-up, the MS-CRI group showed a slight regression tendency (P < .001) and the TICL group was stable for the astigmatism correction (P = .510). At 6 months postoperatively, the mean magnitudes of the surgically induced astigmatism were 1.46 ± 0.53 and 1.10 ± 0.48 diopters (P < .001). The correction index of the TICL group was closer to 1 compared to that of the MS-CRI group (0.95 vs 0.76). Approximately 99% of eyes in the TICL group had angle of error within ±15°, whereas 89% eyes in the MS-CRI group were within that range. A significant relationship between the magnitudes of target induced astigmatism and correction index was noted in the MS-CRI group (P < .001), but not in the TICL group (P = .592).

CONCLUSIONS

TICL implantation could achieve better visual outcomes for correcting moderate to high astigmatism compared to ICL implantation plus MS-CRI. [J Refract Surg. 2023;39(8):539-545.].

Differential compensatory role of internal astigmatism in school children and adults: The Hong Kong Children Eye Study

BACKGROUND

To compare the prevalence of refractive (RA), corneal (CA), and internal astigmatism (IA) in Hong Kong children and adults and evaluate the role of IA in compensating for total astigmatism and its relations to myopic traits.

METHODS

The Hong Kong Children Eye Study is a population-based cross-sectional study. Totally 3704 school children (mean age 7.5 ± 1.0 years) and 5577 adults (mean age 41.1 ± 7.5 years), who were their parents, were recruited. Cycloplegic and non-cycloplegic refractive cylinders were obtained from children and adults, respectively. Spearman correlation was applied to detect associations between astigmatism, ocular biometrics, refraction, and lens power. Astigmatism compensation factor (CF) was derived from the power vector analysis J0 and J45.

RESULTS

The prevalence of RA (≤-1.0 D), CA (≥+1.0 D) and IA (≥+1.0 D) was 21.9%, 63.9%, and 9.9% in children, and 30.9%, 39.5%, and 23.7% in adults respectively. The mean RA, CA and IA values in children and adults were -0.69 ± 0.66 D, +1.14 ± 0.61 D, +0.62 ± 0.32 D, and -0.80 ± 0.74 D, +0.97 ± 0.69 D, and +0.76 ± 0.43 D, respectively. In adults and children, IA was negatively correlated with axial length (p < 0.0001), but positively correlated with spherical values and equivalent (p < 0.0001), suggesting an association of astigmatism with myopic traits. A greater proportion of children exhibited compensation by IA than adults in J0 (86.6% vs. 66.0%, p < 0.0001) and J45 components (55.5% vs. 41.7%, p < 0.0001).

CONCLUSIONS

Chinese children in Hong Kong exhibit a higher prevalence of RA and CA than in other cities. Children displayed a greater compensation by IA than adults, suggesting an age-related attenuation of IA compensation. IA is associated with myopic traits.

The effects of programmed optical zones on achieved corneal refractive power with myopic astigmatism after small incision lenticule extraction (SMILE): a vector analysis

PURPOSE

To evaluate the effects of different programmed optical zones (POZs) on achieved corneal refractive power (CRP) with myopic astigmatism after small incision lenticule extraction (SMILE).

METHODS

In total, 113 patients (113 eyes) were included in this retrospective study. The eyes were divided into two groups according to POZ: group A (6.5, 6.6, and 6.7 mm, n = 59) and group B (6.8, 6.9, and 7.0 mm, n = 54). Fourier vector analysis was applied to evaluate the error values between the attempted and achieved corneal refractive power (CRP). Alpins vector analysis was used to calculate surgically induced astigmatism (SIA), difference vector (DV), magnitude of error (ME), and astigmatism correction index (ACI). Multivariate regression analysis was performed to assess potential factors associated with the error values.

RESULTS

The error values in the group with large POZ were closer to zero, and significantly associated with the POZ at 2 and 4 mm of the cornea (β =  - 0.50, 95% confidence interval [CI] [- 0.80, - 0.20]; β =  - 0.37, 95% CI [- 0.63, - 0.10], P < 0.05, respectively). For the correction of astigmatism, the values of SIA, ME, and ACI were lower in group B than in group A (P < 0.05). The fitting curves between TIA and SIA were y = 0.83x + 0.19 (R² = 0.84) and y = 1.05x + 0.04 (R² = 0.90), respectively.

CONCLUSIONS

Smaller POZs resulted in higher error values between the achieved- and attempted-CRP in the SMILE procedure, which should be considered when performing surgery.

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.

Comparative study of functional optical zone: small incision lenticule extraction versus femtosecond laser assisted excimer laser keratomileusis

AIM

To investigate the size of functional optical zone (FOZ) after small incision lenticule extraction (SMILE) versus femtosecond laser assisted excimer laser keratomileusis (FS-LASIK) for myopia correction and potential associated factors for FOZ.

METHODS

A total of 133 patients who received corneal refractive surgery in our hospital between November 2018 and July 2021 were retrospectively enrolled. There were 63 patients (123 eyes) in SMILE group and 70 patients (139 eyes) in FS-LASIK group. The size of FOZ was measured using Pentacam 3-dementional anterior segment analyzer before and 3mo after surgery, so as to analyze postoperative achieved functional optical zone (AFOZ) and its contributing parameters.

RESULTS

When planned functional optical zone (PFOZ) was 6.5 mm for both groups, AFOZ was 1.45±0.27 and 1.67±0.25 mm smaller than preoperative FOZ in SMILE group and FS-LASIK group 3mo after surgery. AFOZ in SMILE group was significantly larger than that in FS-LASIK group (P<0.001). Variation of FOZ was negatively correlated with preoperative spherical equivalent (SE) and positively correlated with variation of mean keratometry value (ΔKm), variation of spherical aberration (ΔSA), and variation of Q-value (ΔQ, all P<0.001) in both groups. Multiple variable linear regression equations were ΔFOZ=1.354-0.1×pre-SE+0.336×ΔQ+1.462×ΔSA in SMILE group and ΔFOZ=1.512+0.137×ΔQ+0.468×ΔSA in FS-LASIK group.

CONCLUSION

AFOZ is significantly smaller than preoperative FOZ in both SMILE and FS-LASIK groups. With the same PFOZ, larger AFOZ is achieved in SMILE group than in FS-LASIK group.

Evaluation of the Effects of Myopic Astigmatism Correction and Anterior Corneal Curvature on Functional Optical Zone After SMILE

PURPOSE

To evaluate the influence of different degrees of myopic astigmatism correction and preoperative anterior corneal curvature on the functional optical zone (FOZ) following small incision lenticule extraction (SMILE).

METHODS

In this retrospective study, 68 patients (106 eyes) treated with SMILE were grouped according to myopic astigmatism correction: control (0.00 diopters [D]), moderate astigmatism (-0.50 to -2.00 D), and high astigmatism (> -2.00 D). The FOZ was measured and compared between the three groups for 3 months. Correlations between attempted correction, anterior corneal curvature, corneal aberrations, and the FOZ were analyzed.

RESULTS

The preoperative mean treatment spherical equivalent was comparable among the three groups. The average FOZ was 5.06 ± 0.24 mm in the control group, 5.19 ± 0.25 mm in the moderate astigmatism group, and 5.35 ± 0.20 mm in the high astigmatism group The FOZ showed statistically significant differences among the three groups (P < .001), particularly between the high astigmatism group and the other two groups (P < .001 and .018). Correlation analysis showed that the total higher order aberrations, coma, and spherical aberration change were correlated with the FOZ (P < .001). Preoperative steep keratometry, average keratometry, and corneal astigmatism were significantly correlated with the FOZ (P < .05). The correlation remained after excluding the influence of attempted correction on the FOZ (P < .05). After adjusting for other risk factors using multiple linear regression analysis, there was still a significant positive association between preoperative steep keratometry and the FOZ (P < .001).

CONCLUSIONS

Patients with higher myopic astigmatism achieved a larger FOZ and less induced horizontal coma than the control and moderate astigmatism groups. A larger FOZ after SMILE can be achieved in eyes with steeper keratometry. [J Refract Surg. 2023;39(2):135-141.].

Effect of keratometric astigmatism on visual outcomes following small incision lenticule extraction

Purpose

To investigate the influence of keratometric astigmatism on visual outcomes following small incision lenticule extraction (SMILE).

Methods

Eighty eyes undergoing SMILE for myopia correction were classified into two groups based on preoperative keratometric astigmatism: low keratometric astigmatism (LA) and high keratometric astigmatism (HA) groups. Refractive outcomes, vector components, and changes in higher order aberrations (HOAs) were evaluated preoperatively and 6 months postoperatively.

Results

At the postoperative 6-month visit, no significant difference was observed in the decentered distance between the HA and LA groups (HA: 0.17 ± 0.08 mm, LA: 0.16 ± 0.08 mm, P = 0.189). No significant differences in the correction index (P = 0.481), absolute angle of error (P = 0.104), or index of success (P = 0.147) were observed between the two groups. There was no significant difference in the induction of corneal aberrations between the two groups. Furthermore, there were no significant associations between the decentered distance and the vector components of astigmatic correction or induction of higher-order aberration in the HA group (P ≥ 0.294, P ≥ 0.112) or the LA group (P ≥ 0.323, P ≥ 0.080).

Conclusions

SMILE for high keratometric astigmatism could achieve comparable treatment centration and visual quality to that of low keratometric astigmatism

Twelve-year global publications on small incision lenticule extraction: A bibliometric analysis

Purpose

To analyze the development process of small incision lenticule extraction (SMILE) surgery in a 12-year period.

Methods

We conducted a literature search for SMILE research from 2011 to 2022 using the Science Citation Index Expanded (SCIE) of the Web of Science Core Collection (WoSCC). The VOS viewer, and CiteSpace software were used to perform the bibliometric analysis. Publication language, annual growth trend, countries/regions and institutions, journals, keywords, references, and citation bursts were analyzed.

Results

A total of 731 publications from 2011 to 2022 were retrieved. Annual publication records grew from two to more than 100 during this period. China had the highest number of publications (n = 326). Sixty-five keywords that appeared more than four times were classified into six clusters: femtosecond laser technology, dry eye, biomechanics, visual quality, complications, and hyperopia.

Conclusion

The number of literatures has been growing rapidly in the past 12 years. Our study provides a deep insight into publications on SMILE for researchers and clinicians with bibliometric analysis for the first time.

Photorefractive Keratectomy Enhancement (PRK) After Small-Incision Lenticule Extraction (SMILE)

Purpose

To determine rates of enhancement and visual prognosis following photorefractive keratectomy (PRK) enhancement of small-incision lenticule extraction (SMILE).

Patients and Methods

This retrospective, single-site study reviewed all cases of primary SMILE at Hoopes Vision in Draper, Utah between March 14, 2017 and April 8, 2022 to identify any cases that required follow-up enhancement. Primary SMILE was performed using Visumax 500 kHz femtosecond laser (Carl Zeiss Meditec, Jena, Germany). All enhancements were performed with alcohol-assisted PRK, using a WaveLight EX500 excimer laser (Alcon Laboratories, Inc., Fort Worth, TX).

Results

Four hundred and five eyes underwent primary SMILE, of which 15 later underwent PRK enhancement (enhancement rate of 3.7%). No significant difference in pre-SMILE data was identified between the enhancement and non-enhancement groups. The average age of those who underwent PRK enhancement was 33.8±6.3 years old and ranged from 25 to 45. Following primary SMILE, 13 eyes (87%) had an uncorrected distance visual acuity (UDVA) of 20/40 or better, and none had a UDVA of 20/20 or better. After one year of post-enhancement follow-up, all eyes had a UDVA of 20/40 or better, and 13 eyes (87%) had a UDVA of 20/20 or better (Figure 1). All were within one diopter of target spherical equivalent (SEQ), 13 (87%) were within 0.50 D, and 10 (67%) were within 0.25 D. Of those with 12-month follow-up data, none had UDVA worse than corrected distance visual acuity (CDVA), and none had lost lines of CDVA. Efficacy and safety indices were 1.03 and 0.99, respectively.

Conclusion

Following SMILE, ophthalmologists may anticipate an enhancement rate of one to seven percent. In these cases, PRK is a safe and effective procedure for enhancement of SMILE.

Simple method of measuring ocular rotation in supine position during small incision lenticule extraction

AIM

To introduce a novel measurement method of static cyclotorsion in small incision lenticule extraction (SMILE) and to investigate the effect of preoperative parameters on cyclotorsion and the effect of cyclotorsion on postoperative outcomes.

METHODS

The medical records of 242 patients and 484 eyes who underwent SMILE surgery were retrospectively reviewed. Preoperative intraocular pressure, refractive error, and corneal thickness were investigated. Refractive values and visual acuity were measured at 1d, 1, 3, and 6mo. Ocular cyclotorsion in the supine position was measured by calculating the location and angle of the incision site of the cornea in the anterior slit photograph taken after surgery.

RESULTS

Of the total 484 eyes in 242 patients, preoperative mean spherical equivalent (SE) was -4.10±1.64 D, and the mean astigmatism was -0.82±0.74 D. Uncorrected distance visual acuity (UCVA) and SE improved significantly after the surgery. Moreover, 219 (45.2%) eyes had excyclotorsion, 235 (48.6%) eyes had incyclotorsion, and 30 (6.2%) eyes had no torsion. The right eyes tended to be excyclotorted, and the left eyes tended to be incyclotorted (P<0.01). The mean cyclotorsion was 1.18°±3.69°, and the mean absolute value of cyclotorsion was 3.14°±2.26°. The range of cyclotorsion was 0.5°-11.4°. It was found that the smaller the preoperative sphere, the higher the amount of cyclotorsion (r=0.11, P=0.016). There was no significant association between the amount of cyclotorsion and preoperative astigmatism. There was no correlation between sex, preoperative corneal thickness, preoperative intraocular pressure, amount of cyclotorsion, and direction of cyclotorsion. The ratio of right eye excyclotorsion and left eye incyclotorsion on 1d was higher than that at 1, 3, and 6mo (all P<0.01). There was no difference between the 1, 3, and 6mo results in the right and left eyes (P=0.15, P=0.16, respectively).

CONCLUSION

The newly devised ocular cyclotorsion measurement method can be used to evaluate ocular cyclotorsion after SMILE. Preoperative SE is associated with the amount of cyclotorsion, however, cyclotorsion doesn't have a significant effect on the results of SMILE surgery.

Achieved and Functional Optical Zone in Myopic Eyes With High Astigmatism After Small Incision Lenticule Extraction

PURPOSE

To investigate the achieved optical zone and functional optical zone in myopic eyes with high astigmatism after small incision lenticule extraction (SMILE).

METHODS

Seventy-five eyes of 75 consecutive patients with myopia before SMILE were included and divided into two groups (no astigmatism group: without astigmatism vs high astigmatism group: with astigmatism > 2.00 diopters). The achieved optical zone, functional optical zone, and corneal aberrations were compared using Scheimpflug imaging at 6 months postoperatively. Correlations between corneal aberrations and functional optical zone were analyzed.

RESULTS

The mean achieved optical zone diameter was smaller in the no astigmatism group than in the high astigmatism group. There were no significant differences in achieved optical zone among the different meridians in each group. The mean functional optical zone diameter was significantly smaller in the no astigmatism group than in the high astigmatism group. Compared with the programmed optical zone, significant reduction of the functional optical zone was found in the two groups. The reduction of the functional optical zone was significantly smaller in the high astigmatism group than in the no astigmatism group, except for the 60°, 90°, and 120° meridians. There were significant correlations between the functional optical zone area and the induced corneal aberrations in the high astigmatism group, except for horizontal coma, whereas significant correlations of functional optical zone with total higher order aberrations and spherical aberration were detected in the no astigmatism group.

CONCLUSIONS

Myopic eyes with high astigmatism following SMILE had a circular achieved optical zone, but the functional optical zone was oval and larger than in eyes without astigmatism. Moreover, a lower spherical aberration was observed in the patients with high astigmatism. [J Refract Surg. 2022;38(4):243-249.].

Vector analysis of moderate to high myopic astigmatism after small-incision lenticule extraction (SMILE): 12-month follow-up

PURPOSE

To evaluate the refractive outcomes of small-incision lenticule extraction (SMILE) surgery in moderate to high myopic astigmatism.

STUDY DESIGN

Prospective interventional case series.

METHODS

This study evaluated 111 eyes of 68 patients treated with femtosecond SMILE surgery for the correction of myopia and astigmatism. Inclusion criteria were myopia of - 0.5 D or more and astigmatism between - 1.0 D and -5.0 D. Refractive and visual measurements were obtained preoperatively, 1 and 12 month(s) postoperatively. Vector analysis was used to study the astigmatic outcomes at 12-month follow-up. Comparison of results in two groups of patients with astigmatism below and over 3.00 D was performed.

RESULTS

The preoperative mean spherical equivalent was -5.48 ± 2.17 D (range - 1.75 to - 10.00 D) and the mean cylinder was -2.02 ± 1.09 D (range - 1.00 to - 5.00 D). The mean postoperative cylinder value was -0.60 ± 0.52 D at 12-month visit. The 12-month safety and efficacy indices were 0.98 ± 0.07 and 0.97 ± 0.12, respectively. The high astigmatism group showed significantly lower safety and efficacy indices. The postoperative residual astigmatism was 0.5 D or less in 73% of the eyes. Higher amount of residual astigmatism was observed in the high astigmatism group. The angle of error was ± 5 degrees in 49% and ± 15 degrees in 87% of the eyes.

CONCLUSION

SMILE surgery is effective and safe method for correcting myopic astigmatism. Vector analysis indicated a tendency for the under correction of astigmatism in subjects with high astigmatism.

Corneal Epithelial Thickness Changes Following SMILE for Myopia With High Astigmatism

PURPOSE

To evaluate the corneal epithelial thickness (CET) profile changes after small incision lenticule extraction (SMILE) surgery for myopic astigmatism correction of greater than 2.00 diopters (D).

METHODS

This prospective observational study included 40 eyes (23 patients) treated with SMILE for myopia with cylinders of -2.25 to -4.50 D. Along with standard ophthalmic examinations, CET maps with a diameter of 9 mm were measured by high-resolution spectral-domain optical coherence tomography preoperatively and postoperatively. Correlations between the degree of residual astigmatism and the difference in CET values between preoperative flat and steep meridians were analyzed.

RESULTS

The CET showed significant changes in the central (2 mm), paracentral (2 to 5 mm), midperipheral (5 to 7 mm), and peripheral (7 to 9 mm) zones 6 months after SMILE (P < .001). Among the regions, the CET in the paracentral zones displayed the largest increase (9.75%) with the highest average thickness (57.29 µm). Moreover, symmetrical regional epithelial thickening at the preoperative astigmatism axis was observed in the midperipheral zones. The difference in CET between preoperative flat and steep meridians in the mid-peripheral zones continuously increased from postoperative 1 day to 6 months. This difference was positively correlated with the residual cylinder errors at 6 months postoperatively (r = -0.334, P = .035).

CONCLUSIONS

The 9-mm diameter CET in eyes with high astigmatism significantly increased 6 months after SMILE. Additionally, the difference in CET between preoperative flat and steep meridians in midperipheral zones may be related to astigmatic undercorrection in SMILE. [J Refract Surg. 2021;37(4):224-230.].

Functional Optical Zone and Visual Quality After Small-Incision Lenticule Extraction for High Myopic Astigmatism

Introduction

The aim of this study was to compare the functional optical zone (FOZ) after correction of high myopic astigmatism and low myopic astigmatism by small-incision lenticule extraction (SMILE).

Methods

In this prospective study, 30 patients who received SMILE for high myopic astigmatism correction (cylinderical diopters ≤ − 2.0D) were enrolled in the high astigmatism group (HA). The control group comprised 40 patients who underwent SMILE for low myopic astigmatism correction (LA; cylinderical diopters ≥ − 0.5D). FOZ was delineated as the area outlined by a change of 0.5D relative to the power at the corneal vertex on the total corneal refractive power map. An ellipse-fitting program (MatLab) was used to calculate some parameters of the FOZ. Visual quality evaluations were also conducted, including evaluations of wavefront aberrations, optical quality, and intraocular scattering, and completion of a quality of life questionnaire. All of the right eyes were analyzed in the study.

Results

The preoperative average treatment spherical equivalent (− 5.77 ± 1.86D vs. − 6.49 ± 1.49D; P = 0.074), lenticule thickness (120.87 ± 23.27 μm vs. 118.53 ± 21.66 μm; P = 0.666), and programmed optical zone (6.58 ± 0.17 mm vs. 6.65 ± 0.18 mm; P = 0.104) were comparable between the HA and LA groups. The long axes (6.99 ± 1.14 mm vs. 5.32 ± 0.61 mm; P < 0.001), short axes (4.66 ± 0.96 mm vs. 4.23 ± 0.64 mm; P = 0.047), and area (25.90 ± 8.03 mm² vs. 17.92 ± 4.36 mm²; P < 0.001) of the FOZ were significantly larger in the HA group than in the LA group. The centration of the FOZ were comparable between the two groups (0.62 ± 0.25 mm vs. 0.70 ± 0.25 mm; P = 0.194). Postoperative spherical aberration was lower in the HA group than in the LA group (0.07 ± 0.05 μm vs. 0.14 ± 0.10 μm; P = 0.001). There was no significant difference in the ocular scatter index (0.80 ± 0.46 vs. 0.73 ± 0.46; P = 0.447), modulated transfer function (MTF)_cutoff (37.89 ± 9.79 cpd vs. 39.78 ± 7.45 cpd; P = 0.363), and Strehl in two dimensions (Strehl2D) ratio (0.20 ± 0.04 vs. 0.20 ± 0.04; P = 0.363) between the HA group and the LA group. There were no significant differences in the scores on quality of life between the HA and LA groups (45.88 ± 2.15 vs. 45.64 ± 1.84; P = 0.423). Correlation analysis revealed that increase in the spherical aberration was significantly correlated with the long axes, short axes and area in the FOZ in both groups.

Conclusion

With a comparable optical design and attempted correction in SMILE, the eyes with higher myopic astigmatism correction achieved larger FOZ than the eyes with lower myopic astigmatism correction. Consequently, less spherical aberration induction was created after higher myopic astigmatism correction. This result may be associated with less corneal volume sculpted by laser for the higher astigmatism treatment, leading to fewer biochemical responses and les change in corneal aspherity. Good retinal image quality and satisfied quality of life were achieved at a comparable level in both study groups.

Early visual quality outcomes after small-incision lenticule extraction surgery for correcting high myopic astigmatism

Background

To evaluate early optical quality outcomes after small-incision lenticule extraction (SMILE) surgery for correcting high myopic astigmatism.

Methods

This retrospective study enrolled 55 eyes from 37 patients who had preoperative myopic astigmatism of ≥2.00 diopters (D) who had been treated with SMILE surgery. Preoperatively, the mean cylinder was − 2.41 ± 0.54 D (range, − 2.00 D to − 4.50 D). The preoperative and postoperative visual outcomes, refraction, and higher-order aberration (HOA) at 1 and 3 months were compared. Refractive astigmatism changes were analyzed by the Alpins vector method.

Results

Three months after SMILE surgery, the average cylinder was − 0.14 ± 0.31 D, and the average astigmatism vector was − 0.09 D × 6.34°. The angle of error (AofE) was limited to within ±10°, and the magnitude of error was limited to within ±1.0 D in all patients. The correction index (CI) was 0.98 ± 0.07, the index of success (IOS) was 0.08 ± 0.13, and the flattening index (FI) was 0.97 ± 0.07. Significant positive correlations were found between IOS and |AofE| (P = 0.000); negative correlations were found between FI and |AofE| (P = 0.000). The postoperative total HOA, spherical aberration, vertical coma aberration, and trefoil 30° were increased significantly compared with preoperative measurements, and the increase in HOA was closely related to preoperative astigmatism (P < 0.05).

Conclusions

SMILE has preferable outcomes for correcting high myopic astigmatism. Axis rotation during the surgery might influence the undercorrection of astigmatism. The increase of HOA after surgery is related to preoperative astigmatism.

Influence of age on small incision lenticule extraction outcomes

PURPOSE

To evaluate the influence of patient's age at the time of surgery on small incision lenticule extraction (SMILE) refractive outcomes.

METHODS

This is a retrospective, consecutive, comparative study. We compared the refractive outcomes after myopic SMILE from two groups of patients divided by age (patients ≤35 and ≥40 years old). All eyes were evaluated preoperatively and at 1 and 6 months postoperatively. Main outcome measures were differences on efficacy, safety, predictability and astigmatic changes by vector analysis with ASSORT software between both study groups.

RESULTS

102 matched eyes of 53 patients were included. Preoperatively, we evidenced no differences in the mean SE or astigmatism between groups. However, 6 months postoperatively we observed a significantly worse mean astigmatism (p=0.019), while not regarding SE, in the older population, with a trend towards undercorrection of the refractive cylinder in the ≥40 group. We also observed a statistically significant difference in the efficacy (0.86-1 month and 0.97-6 months in ≥40group vs 0.97-1 month and 1.07-6 months in the ≤35 group; p=0.003) and safety indexes (0.93-1 month and 1.04-6 months in ≥40 group vs 1.0-1 month and 1.11-6 months in the ≤35 group; p=0.008) at 6 months among groups.

CONCLUSIONS

Post-SMILE refractive outcomes in those patients over 40 years of age, although acceptable, are not as good as those obtained in younger patients, showing a significantly lower efficacy and safety indexes, and poorer astigmatic outcomes, with a tendency towards undercorrection. We hypothetise that the increased corneal stroma stiffness in the aged group modifies the post-SMILE corneal stroma remodelling capacity, thus affecting the SMILE refractive and visual response.

Initial Single-Site Experience Using SMILE for the Treatment of Astigmatism in Myopic Eyes and Comparison of Astigmatic Outcomes with Existing Literature

Purpose

To assess a single site’s initial experience with SMILE for the treatment of myopic astigmatism and compare outcomes and vector analysis results with the US Food and Drug Administration (FDA) results and published literature.

Patients and Methods

Forty-eight eyes (29 patients) with mean preoperative sphere of −5.11 ± 1.31 diopters (D) and cylinder of −1.12 ± 0.60 D underwent SMILE. Visual acuity, refractive, and vector analysis outcomes as well as subjective measures were reported at three and twelve months postoperatively and compared with FDA results and the published literature between 2014 and 2020 involving treatment of patients with mean cylinders of >−0.50 to ≤−3.00 D.

Results

At three and twelve months, 43 and 32 eyes were evaluated, respectively. At twelve months, mean cylinder power was reduced to −0.38 ± 0.38 D with 78.1% achieving ≤±0.50 D. Uncorrected distance visual acuity (UDVA) ≥20/20 was achieved in 77.4% of eyes by twelve months with 100% achieving ≥20/30 UDVA. No loss of corrected distance visual acuity was observed in eyes seen at twelve months. Correction index (CI) at twelve months was 0.90 indicating overall undercorrection of 10%. Twelve-month CI was 0.96, 0.90, and 0.83 in eyes with preoperative cylinders of <−1.00 D, ≥−1.00 to <−2.00 D, and ≥−2.00 D, respectively. Mean angle of error was −1.58 ± 11.61° ranging from −24.22° to 37.75°.

Conclusion

We found SMILE to be an effective and safe means of achieving spectacle independence and improving visual acuity in patients with myopic astigmatism. SMILE has the potential for improved clinical outcomes with better nomogram guidance and advancements in technique. However, surgeons must be aware of the potential for undercorrection in with-the-rule astigmatism and at higher preoperative cylinders and as well as the potential for overcorrection in against-the-rule and lower preoperative cylinder astigmatism.