Comparison of astigmatic correction after femtosecond lenticule extraction and small-incision lenticule extraction for myopic astigmatism

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.

Comparison of clinical outcomes between vector planning and manifest refraction planning in SMILE for myopic astigmatism

PURPOSE

To compare clinical outcomes of small-incision lenticule extraction (SMILE) between manifest refraction (MR) and vector planning for myopic astigmatism with high ocular residual astigmatism (ORA).

SETTING

Yonsei University College of Medicine and Eyereum Eye Clinic, Seoul, South Korea.

DESIGN

Prospective, randomized, comparative case series.

METHODS

Patients with myopic astigmatism and ORA of 0.75 diopters (D) or greater were randomized into the MR or vector planning group and underwent SMILE without applying any nomogram for cylinder correction. Visual acuity, MR, corneal topography, and corneal aberration were measured preoperatively and postoperatively. Outcomes at 6 months postoperatively were compared between the groups.

RESULTS

The study comprised 114 patients (114 eyes): 58 eyes in MR planning and 56 eyes in vector planning. The mean uncorrected and corrected distance visual acuity, safety and efficacy indices were comparable between the 2 groups. Postoperative refractive cylinder reached statistically significant differences between the groups (-0.22 ± 0.18 D and -0.14 ± 0.16 D in the MR and vector planning groups, respectively, P = .02). Postoperative corneal toricity and ORA reached statistically significant lower in the vector planning group.

CONCLUSIONS

In myopic astigmatism with high ORA, MR and vector planning in SMILE were effective with comparable visual outcomes; vector planning showed statistically significant lower postoperative refractive and corneal astigmatism and ORA. Use of vector planning may improve refractive outcomes in SMILE cases with high ORA. However, the results may have been different had a nomogram adjustment been applied, as is often used for cylinder corrections with SMILE.

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.

Small-Incision Lenticule Extraction (SMILE) for the Correction of Myopia with Astigmatism: Outcomes of the United States Food and Drug Administration Premarket Approval Clinical Trial

PURPOSE

To present outcomes of the United States Food and Drug Administration premarket approval clinical trial of small-incision lenticule extraction (SMILE) for the correction of myopia and astigmatism.

DESIGN

Prospective, multicenter clinical trial.

PARTICIPANTS

The study included 357 eyes of 357 patients treated with SMILE (50 for myopia and 307 for myopia with astigmatism). Preoperative sphere ranged between -1.00 and -10.00 diopters (D), with manifest spherical equivalent (MSE) of up to -11.50 D and refractive cylinder of up to -3.00 D.

METHODS

-Participants were followed up for 12 months. Corrected distance visual acuity (CDVA) and uncorrected distance visual acuity (UDVA), stability of the manifest refraction, and vector analysis of refractive cylinder are presented for the 307 eyes treated for myopia with astigmatism. Adverse events (AEs) are presented for all 357 eyes.

MAIN OUTCOME MEASURES

Corrected distance visual acuity, uncorrected distance visual acuity, manifest refraction, astigmatic outcomes, and adverse events.

RESULTS

Of the 307 astigmatic eyes enrolled in the study, 304 were treated successfully. In 3 eyes, the procedure was aborted because of intraoperative suction loss. The mean MSE reduced from -5.39±2.30 D at baseline to -0.01±0.24 D at 12 months. Of all eyes, 95.3% were within 0.50 D of emmetropia at 12 months. The percentage of eyes with UDVA of 20/20 or better was 89.0%. No loss of 2 or more lines of CDVA was observed at the 12-month visit. The refractive cylinder reduced from -1.53±0.70 D at baseline to -0.18±0.31 D at 12 months. The mean correction ratio of refractive cylinder was 0.96±0.16 and a slight undercorrection was apparent for higher attempted corrections of astigmatism. Three intraoperative AEs associated with difficult lenticule removal and resultant cap tear occurred, and all resolved without sequelae at postoperative day 1. During the postoperative period, 8 AEs were recorded, but none of them had significant consequences.

CONCLUSIONS

Small-incision lenticule extraction for the treatment of myopia and astigmatism was safe and effective, and the reported AEs had no significant impact on visual acuity. Slight undercorrection of refractive cylinder requires further attention.

Clinical outcomes of Transepithelial photorefractive keratectomy to treat low to moderate myopic astigmatism

Background

To evaluate the refractive and visual outcomes of Transepithelial photorefractive keratectomy (TransPRK) in the treatment of low to moderate myopic astigmatism.

Methods

This retrospective study enrolled a total of 47 eyes that had undergone Transepithelial photorefractive keratectomy. Preoperative cylinder diopters ranged from − 0.75D to − 2.25D (mean − 1.11 ± 0.40D), and the sphere was between − 1.50D to − 5.75D. Visual outcomes and vector analysis of astigmatism that included error ratio (ER), correction ratio (CR), error of magnitude (EM) and error of angle (EA) were evaluated.

Results

At 6 months after TransPRK, all eyes had an uncorrected distance visual acuity of 20/20 or better, no eyes lost ≥2 lines of corrected distant visual acuity (CDVA), and 93.6% had residual refractive cylinder within ±0.50D of intended correction. On vector analysis, the mean correction ratio for refractive cylinder was 1.03 ± 0.30. The mean error magnitude was − 0.04 ± 0.36. The mean error of angle was 0.44° ± 7.42°and 80.9% of eyes had axis shift within ±10°. The absolute astigmatic error of magnitude was statistically significantly correlated with the intended cylinder correction (r = 0.48, P < 0.01).

Conclusions

TransPRK showed safe, effective and predictable results in the correction of low to moderate astigmatism and myopia.

Effect of the Learning Curve on Visual and Refractive Outcomes of Small-Incision Lenticule Extraction

PURPOSE

To investigate the effect of the learning curve for small-incision lenticule extraction during the first 2 years of experience.

METHODS

Small-incision lenticule extraction was performed using the 500-kHz VisuMax femtosecond laser (Carl Zeiss Meditec) by the same surgeon. The initial 100 patients since the surgeon started operating independently were considered as group 1; the recent 100 patients were considered as group 2. The same laser settings and technique were used. The visual and refractive outcomes were compared between groups at postoperative 1 week and 6 months. Vector analysis was performed for eyes with astigmatic correction.

RESULTS

Two hundred right eyes of 200 patients were included. Age, preoperative corrected visual acuity, manifest refraction, and central corneal thickness were similar between groups (P ≤ 0.154). Postoperatively, the efficacy index at 1 week was better in group 2 (group 1: 0.85 ± 0.16 vs. group 2: 0.91 ± 0.10, P = 0.019) but was similar between groups at 6 months (group 1: 0.91 ± 0.14 vs. group 2: 0.94 ± 0.08, P = 0.181). The safety index was higher in group 2 at 1 week (group 1: 0.93 ± 0.10 vs. group 2: 0.95 ± 0.08, P = 0.045) and 6 months postoperatively (group 1: 0.97 ± 0.07 vs. group 2: 0.99 ± 0.03, P = 0.011). Vector analysis showed that postoperative residual astigmatism and misalignment of astigmatic correction were lower in group 2 than in group 1 (P ≤ 0.039) at 1 week and 6 months. The duration of docking and that of lenticule extraction was shorter in group 2 (P ≤ 0.034).

CONCLUSIONS

Our study showed that faster visual recovery, better safety profile, and more accurate astigmatic correction could be attained with increasing surgical experience.

Results of Intraoperative Manual Cyclotorsion Compensation for Myopic Astigmatism in Patients Undergoing Small Incision Lenticule Extraction (SMILE)

PURPOSE

To study the safety, efficacy, and outcomes of manual cyclotorsion compensation in small incision lenticule extraction (SMILE) for myopic astigmatism.

METHODS

Eligible patients with myopia from -1.00 to -10.00 diopters (D) spherical equivalent with a minimum astigmatism of 0.75 D undergoing SMILE were included. Intraoperative cyclotorsion compensation was performed by gently rotating the cone and aligning the 0° to 180° limbal marks with the horizontal axis of the reticule of the right eye piece of the microscope of the femtosecond laser after activating the suction.

RESULTS

In this study, 81 left eyes from 81 patients were analyzed for vector analysis of astigmatism. The mean cyclotorsion was 5.64° ± 2.55° (range: 2° to 12°). No significant differences were found for surgically induced astigmatism, difference vector, angle of error (AE), correction index, magnitude of error, index of success (IOS), and flattening index between 2 weeks and 3 months postoperatively (P > .05). The eyes were categorized into low (≤ 1.50 D, n = 37) and high (> 1.50 D, n = 44) cylinder groups. At 3 months, intergroup analysis showed a comparable correction index of 0.97 for the low and 0.93 for the high cylinder groups, suggesting a slight undercorrection of 3% and 7%, respectively (P = .14). However, the AE and IOS were significantly lower in the high compared to the low cylinder group (P = .032 and .024 for AE and IOS, respectively), suggesting better alignment of the treatment in the high cylinder group. However, the mean uncorrected distance visual acuity of both groups was comparable (P = .21), suggesting good visual outcomes in the low cylinder group despite a less favorable IOS.

CONCLUSIONS

Manual compensation may be a safe, feasible, and effective approach to refine the results of astigmatism with SMILE, especially in higher degrees of cylinders. [J Refract Surg. 2017;33(8):506-512.].

Comparing a new hydroexpression technique with conventional forceps method for SMILE lenticule removal

BACKGROUND

We described a modified 'hydroexpression' technique for the lenticule removal during small-incision lenticule extraction (SMILE) surgery and compared the results with conventional forceps method.

METHODS

This was a retrospective, comparative study of 50 patients who underwent SMILE surgery by the same surgeon. We compared the 1-week and 3-months postoperative results after SMILE using the hydroexpression technique with the conventional forceps technique. Main outcome measures included uncorrected distance visual acuity, corrected distance visual acuity, refractive accuracy, safety index and efficacy index.

RESULTS

The baseline characteristics were comparable between both groups. At postoperative 1 week, the safety index in forceps and hydroexpression group was 0.93±0.11 and 0.97±0.10, respectively (P=0.246). At 3 months, they were 1.00±0.06 and 0.99±0.09 (P=0.850). For efficacy indices, at 1 week they were 0.84±0.17 and 0.91±0.17 (P=0.158). At 3 months, they were 0.92±0.13 and 0.94±0.19 (P=0.624). All eyes aimed for a plano target. 96% in forceps group and 90% in hydroexpression group were within ±0.50 dioptre (D) in spherical equivalent refraction (SEQ) correction at postoperative 3 months (P=0.567). The mean errors of SEQ correction were -0.10±0.21 D in forceps group and -0.08±0.30 D in hydroexpression group (P=0.705).

CONCLUSION

Hydroexpression was simple and safe and had early results comparable to the conventional forceps technique. This technique was particularly useful for cases with more adhesions between lenticule and anterior cap, thin lenticule cases and for the inexperienced SMILE surgeons.

Influence of corneal power on circumpapillary retinal nerve fiber layer and optic nerve head measurements by spectral-domain optical coherence tomography

AIM

To evaluate the influence of corneal power on circumpapillary retinal nerve fiber layer (cpRNFL) and optic nerve head (ONH) measurements by spectral-domain optical coherence tomography (SD-OCT).

METHODS

Twenty-five eyes of 25 healthy participants (mean age 23.6±3.6y) were imaged by SD-OCT using horizontal raster scans. Disposable soft contact lenses of different powers (from -11 to +5 diopters including 0 diopter) were worn to induce 2-diopter changes in corneal power. Differences in the cpRNFL and ONH measurements per diopter of change in corneal power were analyzed.

RESULTS

As corneal power increased by 1 diopter, total and quadrant cpRNFL thicknesses, except for the nasal sector, decreased by --0.19 to -0.32 µm (P<0.01). Furthermore, the disc, cup, and rim areas decreased by -0.017, -0.007, and -0.015 mm², respectively (P<0.001); the cup and rim volumes decreased by -0.0013 and -0.006 mm³, respectively (P<0.01); and the vertical and horizontal disc diameters decreased by -0.006 and -0.007 mm, respectively (P<0.001).

CONCLUSION

For more precise OCT imaging, the ocular magnification should be corrected by considering both the axial length and corneal power. However, the effect of corneal power changes on cpRNFL thickness and ONH topography are small when compare with those of the axial length.

Small-incision lenticule extraction versus femtosecond lenticule extraction for myopic: a systematic review and Meta-analysis

AIM

To examine differences in efficacy, accuracy, safety, aberrations and corneal biomechanical between Small incision lenticule extraction (SMILE) and femtosecond lenticule extraction (FLEx) for myopia.

METHODS

Comprehensive studies were conducted on the PubMed, MEDLINE, EMBASE, and Cochrane Controlled Trials Register before 31 July, 2015. Meta-analyses were performed on the primary outcomes [loss of ≥2 lines of corrected distance visual acuity (CDVA), uncorrected distance visual acuity (UDVA) ≥20/20, spherical equivalent (SE) within ±0.50 diopters (D), final refractive SE], secondary outcomes were high-order aberrations (HOAs) and corneal biomechanical [central corneal thickness (CCT), corneal hysteresis (CH) and corneal resistance factor (CRF)].

RESULTS

Seven trials describing a total of 320 eyes with myopia were included in this Meta-analysis. No significant differences were found in the efficacy [UDVA weighted mean difference (WMD) -0.01; 95%CI: -0.04 to 0.01; P=0.37, UDVA ≥20/20, OR 1.49; 95%CI: 0.78 to 2.86; P=0.23], accuracy (SE WMD -0.03; 95%CI: -0.12 to 0.07; P=0.58, SE within ±0.5 D OR 1.25; 95%CI: 0.34 to 4.65; P=0.74), HOAs (WMD -0.04; 95%CI: -0.09 to 0.01; P=0.14) and CCT WMD 1.83; 95%CI: -7.07 to 10.72; P=0.69, CH WMD -0.01; 95%CI: -0.42 to 0.40; P=0.97, CRF WMD 0.17; 95%CI: -0.33 to 0.67; P=0.50) in the last fellow-up. But for safety, FLEx may achieve fewer CDVA lost two or more two lines (OR 11.11; 95%CI: 1.27 to 96.86; P=0.03) than SMILE, however CDVA (WMD 0.00; 95%CI: -0.03 to 0.02; P=0.77) is similar.

CONCLUSION

SMILE and FLEx are comparable in terms of both efficacy, accuracy, aberrations and corneal biomechanical measures in the follow-up, but FLEx seems to be better in safety measures. The results should be interpreted cautiously since relevant evidence is still limited, although it is accumulating. Further large-scale, well-designed randomized controlled trials are urgently needed.

Effect of location of opening incision on astigmatic correction after small-incision lenticule extraction

We compared the visual and refractive outcomes between 2 different incisional sites in small incision lenticule extraction (SMILE) for low myopic astigmatism. This was a contralateral eye study. Consecutive cases that underwent bilateral SMILE surgery were included. Procedures for both eyes were identical apart from the location of opening incision. The incision was set on the temporal side for the right eye (Group 1), while a superior incision was set for the left eye (Group 2). Twenty-nine patients with a mean age of 35.0 ± 9.6 years were included. Preoperative visual and refractive parameters were comparable between the 2 groups (p > 0.250). At 3 months, the logMAR uncorrected distance visual acuity was 0.074 ± 0.090 in Group 1 and 0.084 ± 0.130 in Group 2 (p = 0.861). No difference was found in the postoperative manifest spherical equivalent (p = 0.501) and manifest cylinder (p = 0.178) between the 2 groups. The efficacy index was 0.85 ± 0.16 in Group 1 and 0.85 ± 0.20 in Group 2 (p = 0.828). Astigmatic correction was not significantly affected by the location of opening incisions using vector analysis. Our study did not find significant differences in visual and refractive outcomes with temporal or superior opening incision during SMILE surgery.

Early outcomes after small incision lenticule extraction and photorefractive keratectomy for correction of high myopia

We prospectively compared visual and refractive outcomes in patients with high myopia and myopic astigmatism after small-incision lenticule extraction (SMILE) and photorefractive keratetctomy (PRK) with mitomycin C. Sixty-six eyes of 33 patients (mean age, 29.7 ± 5.6 years) were included (SMILE: 34 eyes, PRK 32 eyes). Preoperatively, no significant difference was noted in manifest spherical equivalent (p = 0.326), manifest sphere (p = 0.277), and manifest cylinder (p = 0.625) between both groups. At 1 month, there were significant differences in logMAR uncorrected distance visual acuity, efficacy index and manifest refraction spherical equivalent between SMILE and PRK (p ≤ 0.029). At 6 months, the logMAR corrected distance visual acuity (p = 0.594), logMAR uncorrected visual acuity (p = 0.452), efficacy index (p = 0.215) and safety index was (p = 0.537) was comparable between SMILE and PRK. Significant differences were observed in postoperative manifest spherical equivalent (p = 0.044) and manifest cylinder (p = 0.014) between both groups. At the end of 6 months, 100% of the eyes in SMILE group and 69% of the eyes in PRK group were within ±0.50 D of the attempted cylindrical correction. The postoperative difference vector, magnitude of error and absolute angle of error were significantly smaller after SMILE compared to PRK (p ≤ 0.040) implying a trend towards overcorrection of cylindrical correction following PRK.