Early clinical outcomes, including efficacy and endothelial cell loss, of refractive lenticule extraction using a 500 kHz femtosecond laser to correct myopia

Seven-year corneal densitometry changes after small incision lenticule extraction and femtosecond laser-assisted in situ keratomileusis

This study aims to investigate the 7-year changes in corneal densitometry (CD) after small incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK). Forty-two eyes undergoing SMILE and thirty-one undergoing FS-LASIK were included in this retrospective study. CD was measured preoperatively and at 3 and 7 years postoperatively. Three concentric radial zones (0-2, 2-6, and 6-10 mm) of three different corneal depths (anterior 120 μm, posterior 60 μm, and central layer) were analyzed. In all three zones of the three corneal layers, no significant difference in CD was found between the two groups preoperatively and at 3 and 7 years postoperatively (all P > 0.05). All CD values in the three zones of the anterior and central layers significantly declined at 3 years postoperatively (all P < 0.001), and then increased at 7 years postoperatively compared to corresponding 3-year values (all P < 0.01). In the posterior layer, CD values in the 0-2-mm and 2-6-mm zones decreased at 3 years postoperatively (all P < 0.01) and continued to decrease at 7 years postoperatively (all P < 0.01). Similar CD trends were observed after SMILE and FS-LASIK. Posterior layer CD showed a decrease throughout the study period. In the anterior and central layers, CD values decreased and then increased at 7 years postoperatively. The transparency changes might have been due to age-related three-dimensional growth of collagen fibers and wound-healing reactions.

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.

Ex-vivo study on the surface quality of corneal lenticule and stroma after low energy femtosecond laser lenticule extraction

This study aimed to assess the surface quality of cap, stroma and lenticular surfaces created using low-energy femtosecond laser lenticule extraction (Ziemer FEMTO LDV Z8). Twenty-four porcine eyes were divided into four groups (n = 6 each): two with optimal laser power (32%) with posterior curvature equivalent to a spherical correction of -2D and -5D, respectively and the other two with high power (64%) with spherical correction of -2D and -5D respectively. Samples were analysed using scanning electron microscopy (SEM). Surface morphology was evaluated using a standard scoring system; surface relief, surface regularity, extent and position of irregularities were graded by four independent clinicians. Eyes with 32% power and -2D correction had significantly less size of the irregular area than those with -5D; however, no significant difference was found between the two groups with 64% power. When comparing eyes with -2D correction, the size of the irregular area was lesser with 32% power. Surface relief was lesser with -5D correction with 32% power than 64% power. Low-energy femtosecond laser lenticule extraction (Ziemer FEMTO LDV Z8) produces good surface quality results. There is a tendency for smoother surface stromal quality with lower power settings than a higher power.

Comparison Between the Effect of Femtosecond Laser in situ Keratomileusis (FS-LASIK) and Femtosecond Small Incision Lenticule Extraction (FS-SMILE) on the Corneal Endothelium

Purpose

To compare the effect of FS-LASIK and FS-SMILE on the corneal endothelial cell density (ECD) and morphology.

Patients and Methods

This is a prospective, cohort observational study that included 80 eyes of two equal groups of patients. Forty eyes were subjected to the FS-LASIK, and 40 eyes were subjected to the FS-SMILE. In both groups, patients, age ranged between 19 and 37 years with myopia ranges from −0.75 to −9.00 diopters (D) and astigmatism up to −3.00D. The ECD, coefficient of variation (CV), and hexagonality (HEX) in both groups were compared over six months. Specular microscopy was used to evaluate the corneal endothelium throughout the study.

Results

In both groups, ECD showed a statistically significant decrease while CV showed a statistically significant increase in the first month postoperatively. The FS-SMILE had more impact on both ECD and CV until the third and six months, respectively. Hexagonality showed a significant decrease in both groups throughout the whole study. In both groups, no vision-threatening complications occurred, and no eyes developed any corneal complications over a six-month follow-up period.

Conclusion

Although the ECD, CV, HEX are statistically affected in both FS-LASIK and FS-SMILE groups, both procedures have no significant adverse effects on the ECD and morphology. The impact of the FS-SMILE group may be due to the deeper penetration of the femto laser in the corneal tissue compared to the FS-LASIK. The closer the femto laser to the endothelium, the more exposure to the shock waves and heat energy, although minimal but it can cause collateral damage to this layer. The effects of FS-SMILE surgery on corneal endothelial cells and morphology need further investigations.

Incidence and management of intraoperative complications during small-incision lenticule extraction in 3004 cases

PURPOSE

To assess the intraoperative complications during small-incision lenticule extraction (SMILE) for myopia and myopic astigmatism correction and evaluate visual outcomes 6 months postoperatively.

SETTING

Tianjin Eye Hospital, Tianjin, China.

DESIGN

Retrospective case series.

METHODS

Patients who had small-incision lenticule extraction surgery were examined 1 day, 7 days, 1 month, 3 months, and 6 months postoperatively. Demographic characteristics, visual outcomes, and intraoperative complications were recorded. Moreover, the incidence and management of the complications and the potential factors were analyzed.

RESULTS

Of the 3004 eyes (1511 patients), 134 (4.46%) had intraoperative complications, including suction loss (28 cases [0.93%]), incisional bleeding (28 cases [0.93%]), opaque bubble layer (22 cases [0.73%]), subconjunctival hemorrhage (20 cases [0.67%]), black areas (10 cases [0.33%]), unintended posterior plane dissection (10 cases [0.33%]), tearing of the lenticule (8 cases [0.27%]), abrasion at the incision (5 cases [0.17%]), and inaccurate laser pulse placement due to eye movement (3 cases [0.10%]). The complications were resolved instantaneously using appropriate management procedures; all cases had good visual outcomes. Six months postoperatively, 99.80% of cases had an uncorrected distance visual acuity better than 20/25 and the mean corrected distance visual acuity was -0.06 logarithm of the minimum angle of resolution ± 0.07 (SD).

CONCLUSIONS

Although small-incision lenticule extraction shows promising outcomes for correction of myopia and myopic astigmatism, intraoperative complications still inevitably occur. However, satisfactory visual outcomes may be achieved using appropriate management techniques.

Fluctuation in straylight measurements during the visual recovery phase after small incision lenticule extraction

PURPOSE

To investigate the postoperative straylight changes during the visual recovery phase after small incision lenticule extraction (SMILE) and their association.

METHODS

Seventy consecutive eyes from 37 patients with a mean age of 30.92 ± 7.26 years and a mean preoperative spherical equivalent of -5.24 ± 1.90 dioptres undergoing myopic or myopic astigmatism SMILE correction were included in this prospective study. Patients were followed up at days 1, 3, 7, 14, 21 and 28 after standard SMILE. Straylight was measured using the C-Quant straylight meter (Oculus GmbH, Germany) preoperatively and at each postoperative visit.

RESULTS

Preoperatively, the mean straylight measurement was 1.16 ± 0.16. After SMILE, the mean straylight values were 1.12 ± 0.14 and 1.13 ± 0.13 at days 7 and 14, which were significantly reduced compared to preoperative values (p ≤ 0.028). Straylight returned to baseline by week 3 (p = 0.160) and remained stable onwards (p = 0.651). A lower ablation ratio was associated with less straylight level at days 1, 3, 14 and 21 (p ≤ 0.0497) in the multivariable regression model. Likewise, better visual acuity was associated with lower straylight at days 7, 14 and 28 postoperatively (p ≤ 0.038). A small proportion of eyes (range: 0-12.86%) had ≥0.30 log(s) increase in postoperative straylight within the first month after SMILE.

CONCLUSIONS

SMILE induced a temporary decrease in straylight. It gradually returned to the preoperative level, which could be related to a number of dynamic processes during corneal healing. In the small proportion of patients with an increase in straylight postoperatively, this can affect their visual recovery during the early postoperative period.

The comparison of visual outcomes, aberrations, and Bowman's layer micro-distortions after femtosecond laser small-incision lenticule extraction (SMILE) for the correction of high and moderate myopia and myopic astigmatism

Background

This study compares the clinical outcomes of femtosecond laser small-incision lenticule extraction (SMILE) for the correction of myopia and myopic astigmatism greater than − 10 D, and − 10 D or less respectively.

Methods

60 eyes/patients were equally selected into group 1 (myopia and myopic astigmatism of − 10 D or less) and group 2 (myopia and myopic astigmatism of over − 10 D), both of which were treated with SMILE. Visual and refractive outcomes, corneal higher-order aberrations, and Bowman’s layer micro-distortions were evaluated preoperatively, 3 months, and 6 months postoperatively.

Results

LogMAR corrected distance visual acuity (CDVA) of group 1 and group 2 was − 0.069 ± 0.047 and − 0.053 ± 0.073 6 months postoperatively (P = 0.48). 100% eyes in group 1 and 97% in group 2 were within 1 D of targeted correction (P = 0.45). Meanwhile, 100% eyes in group 1 and 97% in group 2 had an uncorrected distance visual acuity of 20/25 or better (P = 0.20). Changes in corneal higher-order aberrations root mean square, coma, and trefoil were similar between the two groups but spherical aberration was higher in group 2 (P < 0.01). Micro-distortions were observed in 53% in group 1 and 77% in group 2. More micro-distortions were observed in group 2 (3.40 ± 2.66) than in group 1 (2.07 ± 2.29) (P = 0.041). The total number of micro-distortions was not correlated with postoperative CDVA (P = 0.77).

Conclusions

Visual outcomes showed similar results of SMILE for myopic correction of > − 10 D and ≤ − 10 D. Refractive outcomes showed slightly under-correction in higher myopic eyes. Higher myopic treatment tends to induce more spherical aberrations. Micro-distortions had no impact in visual and refractive outcomes.

Comparison of visual quality after EVO-ICL implantation and SMILE to select the appropriate surgical method for high myopia

Background

This study sought to compare the visual quality between intraocular collamer lens (EVO-ICL) implantation and small-incision lenticule extraction (SMILE) and determine the appropriate surgical method to treat patients with high myopia (− 6.25 to − 10 D).

Methods

A total of 48 eyes underwent EVO-ICL implantation and another 48 eyes underwent SMILE. The uncorrected distance visual acuity (UDVA), best-corrected distance visual acuity (BCVA) and equivalent spherical degree were compared across the SMILE (− 6.25 to − 10 D) and EVO-ICL (− 6.25 to − 10 D) implantation groups. Preoperative and postoperative visual quality parameters were compared between and within groups.

Results

The OQAS II values (OV 100%) one week and one month after surgery and the modulation transfer function (MTF), OV 20% and OV 9% values one week after surgery in the SMILE group were lower than the respective preoperative values. The objective scatter index (OSI) value increased one week as well as one month after surgery compared with the preoperative values. The MTF cut-off value of the SMILE group was lower than that of the EVO-ICL implantation group three months after surgery.

Conclusions

For patients with high myopia, the postoperative visual quality of EVO- ICL implantation was slightly better than that of SMILE.

Visual and Refractive Outcomes of Small-Incision Lenticule Extraction in High Myopia: 5-Year Results

Purpose

To report long-term visual and refractive results of small-incision lenticule extraction (SMILE) in treatment of high myopia.

Materials and Methods

Medical records of patients who underwent SMILE for surgical correction of myopia or myopic astigmatism were retrospectively reviewed. Only patients with a preoperative spherical equivalent of subjective manifest refraction (SE) ≥ 6 D and a postoperative follow-up of 5 years were included in the study. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and SE were analyzed preoperatively and at 1-, 3-, and 5-year postoperative periods.

Results

Thirty-seven eyes of 37 patients were included in the study. The mean attempted SE was −7.47 ± 1.10 D (range −6.00 to −10.00 D). At the 5-year visit, the mean difference between achieved and attempted SE was −0.43 ± 0.47 (0.50 to −1.25 D). Mean postoperative UDVA and CDVA were 0.20 ± 0.18 and 0.06 ± 0.08 logMAR, respectively. At the 1-year visit, 70% and 97% of the eyes were within ±0.50 D and ±1.00 D of the intended correction. At the 5-year follow-up, 59% and 92% percent of the eyes were within ±0.50 D and ±1.00 D of the intended SE, respectively. At the 5-year visit, the efficacy index was 0.89 ± 0.26 and the safety index was 1.16 ± 0.20. Fifty-four percent of the eyes gained one or more lines of CDVA.

Conclusion

SMILE with an intended correction of up to a spherical equivalent of 10 D is safe and effective. However, there is regression of the refractive effect over extended follow-up.

Two-years results of small-incision lenticule extraction and wavefront-guided laser in situ keratomileusis for Myopia

PURPOSE

To compare the 2-years visual and refractive outcomes between small-incision lenticule extraction (SMILE) and wavefront-guided laser in situ keratomileusis (LASIK) in eyes with myopia and myopic astigmatism.

METHODS

Our retrospective case-control study examined 30 eyes of 30 patients with the manifest refraction spherical equivalent (MRSE) of -3.71 ± 1.83 dioptres (D) who underwent SMILE and 30 eyes of 30 patients with MRSE of -3.81 ± 1.40 D who underwent wavefront-guided LASIK. We assessed the 2-years clinical outcomes.

RESULTS

Logarithm of the minimal angle of resolution (LogMAR)-corrected distance visual acuity (CDVA) was -0.23 ± 0.07 in the SMILE group and -0.24 ± 0.07 in the wavefront-guided LASIK group 2 years postoperatively (p = 0.82). Logarithm of the minimal angle of resolution-uncorrected distance visual acuity (UDVA) was -0.18 ± 0.09 and -0.15 ± 0.11 (p = 0.30, respectively). In the SMILE and wavefront-guided LASIK groups 2 years postoperatively, 100% and 73% of eyes, respectively, were within 0.5 D of the prompted MRSE correction (p = 0.005). Changes in the MRSE of -0.10 ± 0.30 D and -0.23 ± 0.51 D occurred from 3 months to 2 years (p = 0.40, respectively). We found a significant correlation between myopic regression and the changes in the keratometric readings from 3 months to 2 years after wavefront-guided LASIK (r = -0.48, p = 0.002), but not after SMILE (r = -0.004, p = 0.90).

CONCLUSION

Small-incision lenticule extraction offers better refractive outcomes than wavefront-guided LASIK during a 2-years follow-up for the correction of myopia and myopic astigmatism.

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.

A Nomogram to Improve Predictability of Small-Incision Lenticule Extraction Surgery

Background

This study aimed to determine and validate that use of a nomogram could enhance the predictability of small-incision lenticule extraction (SMILE) surgery.

Material/Methods

195 eyes from 98 patients were enrolled in group 1, and 46 eyes from 26 patients in group 2. Uncorrected and corrected distance visual acuity (UDVA and CDVA), manifest refraction spherical equivalent (SE) preoperatively and 1 day, 1 week, 1 month, and 3 months postoperatively were measured. A nomogram based on the error in SE correction was generated by using multifactor regression method in group 1. After applying this nomogram to redesign the refraction target, the predictability, safety, and efficacy of the SMILE procedure were determined.

Results

A linear regression formula (SE error=0.259+0.113×SE_preoperative) was derived as a nomogram to adjust the SE target. In group 2, the predictability of error was 86.21% within 0.50 D and 97.83% within 1.00 D, compared with 70.25% and 95.90%, respectively, in group 1. The use of the nomogram significantly reduced the variance in postoperative SE. The efficacy and safety of SMILE did not differ significantly in the 2 groups 3 months postoperatively.

Conclusions

The nomogram can optimize the target refractive prediction of the SMILE procedure without compromising safety and efficiency.

Lower Laser Energy Levels Lead to Better Visual Recovery After Small-Incision Lenticule Extraction: Prospective Randomized Clinical Trial

PURPOSE

To determine the effect of lowering laser energy on clinical outcomes in small-incision lenticule extraction (SMILE).

DESIGN

Prospective randomized clinical trial.

METHODS

A total of 151 patients (151 eyes) with moderate myopia scheduled for SMILE were included: 58 eyes received SMILE with low energy (100, 105, and 110 nJ; L-SMILE group) and 93 with conventional energy (115-150 nJ; C-SMILE group). Patients received complete ophthalmic examinations preoperatively and over 3 months postoperatively.

RESULTS

Uncorrected distance visual acuity (logMAR UDVA) 1 day and 1 week postoperatively was significantly better in L-SMILE than in C-SMILE (P < .001 and P = .005, respectively). There was no significant difference between the groups at 1 and 3 months. L-SMILE induced significantly fewer corneal aberrations compared with C-SMILE at 1 week and 1 month postoperatively (both P < .01), but there were no significant differences at 3 months. Though there was no difference in logMAR UDVA over the postoperative period between the 100, 105, and 110 nJ subgroups, there was a significant difference in logMAR UDVA on postoperative day 1 between L-SMILE and each subgroup in which an energy level of 115 nJ or higher was used. Furthermore, logMAR UDVA on postoperative day 1 showed a significant correlation with laser energy (r = 0.451, P < .001) and multiple linear regression analysis revealed that energy level was the only independent factor associated with logMAR UDVA on postoperative day 1 (P < .001).

CONCLUSIONS

SMILE using femtosecond energy of less than 115 nJ facilitates better visual acuity with less induction of corneal aberrations in the early postoperative period.

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.

Comparison of biomechanical effects of small incision lenticule extraction and laser-assisted subepithelial keratomileusis

PURPOSE

To compare the corneal biomechanical properties after small incision lenticule extraction (SMILE) group and laser-assisted subepithelial keratomileusis (LASEK) group.

METHODS

The SMILE group comprised 39 patients (75 eyes) while it was 38 patients (76 eyes) in the LASEK group. Corneal hysteresis (CH) and the corneal resistance factor (CRF) parameters were determined using the Ocular Response Analyzer preoperatively and at 1 and 3 months postoperatively.

RESULTS

There were significant differences in the preoperative manifest refraction spherical equivalent (MRSE), central corneal thickness (CCT), the planned ablation depth (AD) or CRF values between the two groups, except for the CH value (p = 0.07). The CH and CRF values at 1 and 3 months postoperatively were significantly lower than the preoperative values in both groups (p < 0.01). The postoperative CH values were significantly lower in the LASEK group than in the SMILE group at both follow-up visits after adjusting for age, sex, preoperative CCT, preoperative SE, planned AD and the use of both eyes in the same subject (p < 0.01). However, no significant differences were observed in postoperative CRF between groups (p = 0.22 at 1 month and p = 0.41 at 3 months). No significant correlation was found between the planned AD and the changes in CH or CRF at any follow-up visit in the SMILE group. The preoperative magnitude of CH and CRF may be predictors of postoperative changes in CH and CRF in the both groups.

CONCLUSIONS

CH and CRF decreased after SMILE and LASEK. However, the changes in the CH values were less after SMILE than after LASEK.

Vision-related quality of life and visual outcomes after small-incision lenticule extraction and laser in situ keratomileusis

PURPOSE

To compare vision-related quality of life (VRQoL) scores and clinical outcomes between small-incision lenticule extraction and laser in situ keratomileusis (LASIK).

SETTING

Singapore National Eye Centre, Singapore.

DESIGN

Prospective study.

METHODS

Patients had small-incision lenticule extraction using the Visumax 500 kHz femtosecond laser; or LASIK excimer ablation with the Wavelight Allegretto 400 Hz laser. Primary outcomes were 3-month predictability, efficacy, and safety. Secondary outcomes were intraoperative experience, visual symptoms, and VRQoL (validated Quality of Life Impact of Refractive Correction [QIRC] questionnaire) in 25 a subgroup of patients in each group. Following Rasch analysis, "Functional" and "Emotional," QIRC dimensions were analysed separately.

RESULTS

At 3 months, predictability (82.5% versus 85.3%, ±0.5 diopters attempted correction, P =.453), safety index (1.13 ± 0.19 [SD] versus 1.07 ± 0.16, P = .158), and efficacy index (0.91 ± 0.21 versus 0.97 ± 0.19; P = .002) were found when comparing small-incision lenticule extraction (172 eyes) and LASIK (matched 688 eyes). Intraoperative experience between groups was not statistically different; visual fluctuations (P = .020) and episodes of visual blurring (P = .008) were greater after small-incision lenticule extraction than after LASIK at 1 month but not at 3 months. There was no difference in "functional" (66.7 ± 15.7 versus 55.3 ± 22.2, P = .064) and "emotional" (42.7 ± 23.2 versus 37.9 ± 23.8, P = .394) QIRC dimensions between the 2 groups (25 patients in each group) at 3 months.

CONCLUSION

The study, 3-month predictability, safety, and VRQL scores were not statistically different between small-incision lenticule extraction and LASIK.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Small Incision Lenticule Extraction for Postkeratoplasty Myopia and Astigmatism

Purpose. To evaluate the visual and refractive outcomes after small incision lenticule extraction (SMILE) for treating myopia and myopic astigmatism after penetrating keratoplasty (PKP). Design. Case-series. Methods. Ten eyes of 10 patients with previous PKP and residual myopic astigmatism for whom pentacam imaging and thickness measurements were acceptable for laser vision correction. Manifest refraction (MR), uncorrected distance visual acuity (UDVA), and corrected distance visual acuity (CDVA) were obtained preoperatively and one day, one week, and one, 3, and 6 months postoperatively. Cases were operated on the VisuMax® femtosecond laser platform with 500 kHz repetition rate. Results. The mean correction ratio for spherical errors was 0.84 ± 0.19 D and for the mean refractive spherical equivalent (MRSE) was 0.79 ± 0.13 D. Vector analysis showed a mean astigmatism reduction at the intended axis of 67 ± 25.25%, a correction index of 0.81 ± 0.21, and an overall mean percentage of success of astigmatism surgery of 53 ± 37.9%. The postoperative MRSE was stable throughout the 6-month follow-up period. The efficacy index was 0.93 and the safety index was 1.12. Conclusion. SMILE for correction of post-PKP myopia and astigmatism is effective, safe, and stable with moderate accuracy and predictability. Centration of the treatment within the grafts was easily performed.

Short-Term Outcomes of Small-Incision Lenticule Extraction (SMILE) for Low, Medium, and High Myopia

Purpose

To determine the safety, efficacy, and predictability of small-incision lenticule extraction at 6-month follow-up, depending on the level of the myopic refractive error. The surgeries were performed by a surgeon new to this technique.

Methods

Seventy-one subjects with a mean age of 31.86 ± 5.57 years were included in this retrospective observational study. Subjects were divided into 3 groups depending on the preoperative spherical equivalent (SE): low group from -1.00 D to -3.00 D, medium from -3.25 D to -5.00 D, and high from -5.25 D to -7.00 D. Manifest refraction, corrected distance visual acuity (CDVA), and uncorrected distance visual acuity (UDVA) were measured before surgery and at 6 months after the treatment.

Results

In total, 1.4% of the eyes lost 1 line of CDVA after the procedure, whereas 95.8% remained unchanged and 2.8% gained 1 line. A significant undercorrection (p = 0.031) was found in the high myopia group (median -0.50 D), whereas the low and medium groups remained near to emmetropia. In terms of efficacy, no statistically significant intergroup differences for postoperative UDVA (p = 0.282) were found. The vector analysis also showed undercorrection of the preoperative cylinder, even though the standard deviations decreased from 0.9 D in the x axis and 0.7 D in the y axis to 0.24 D and 0.27 D, respectively.

Conclusions

Small-incision lenticule extraction might be a safe, effective, and predictable procedure even for inexperienced surgeons. No differences in efficacy were found among myopia levels even though undercorrections were found for SE and cylinder in high myopia.

Short term effects of small incision lenticule extraction surgery on corneal endothelium

AIM

To assess the effects of small incision lenticule extraction (SMILE) surgery on the corneal endothelium at 1d to 1mo postoperatively.

METHODS

A retrospective, observational study was conducted on 47 patients (47 eyes) who received SMILE surgery. Patients were grouped according to contact lens wear condition. The corneal endothelium was examined preoperatively and at 1d, 1wk and 1mo postoperatively. The corneal endothelium was analyzed for endothelial cell density (ECD), percentage of hexagonal cells, and coefficient of variation (CV) of cell size.

RESULTS

There were no significant decrease in the ECD, percentage of hexagonal cells or increase in CV at 1d, 1wk and 1mo postoperatively (P>0.05). However, there was a small increase of ECD by 2.88% in contact lens wearers (78.26±113.62 cell/mm(2), P<0.05).

CONCLUSION

SMILE has no significant adverse effects on the corneal ECD and morphology during 1mo follow-up time.

Intra-Operative Cap Repositioning in Small Incision Lenticule Extraction (SMILE) for Enhanced Visual Recovery

PURPOSE

To study the role of intra-operative cap repositioning in acute visual recovery after small incision lenticule extraction (SMILE).

MATERIALS AND METHODS

Ninety-four eyes of 47 patients underwent the SMILE procedure for correction of myopic refractive error. Manifest refraction and visual quality parameters (optical quality analysis system) were evaluated before surgery. The Bowman's membrane was imaged using a handheld spectral domain optical coherence tomography device. All patients underwent an uneventful SMILE surgery by a single experienced surgeon. Intra-operative cap repositioning was done in the "right" eye of all patients (repositioned group) and the "left" eye of each patient served as controls (non-repositioned group). Visual acuity and optical quality were assessed 1 day and 1 week after surgery.

RESULTS

Bowman's membrane microdistortions were found in 21.3% of eyes in the repositioned group and 59.57% of the eyes in the non-repositioned group (p = 0.003) on the first day after surgery. Comparison of optical quality parameters was carried out between eyes where repositioning was done and control eyes (with and without microdistortions). On the first day after surgery, the modulation transfer function (MTF) and Strehl's ratio (SR) were significantly better in the repositioned group when compared with the controls (p = 0.002 and p = 0.003, respectively). Refractive error and lenticule thickness in eyes with microdistortions were similar (p > 0.05) between the two groups indicating other contributors to acute optical quality postoperatively.

CONCLUSIONS

Although the refractive error before surgery determines the extent of microdistortions, intra-operative cap repositioning can reduce them, thereby expediting acute visual recovery after SMILE.

Visual and refractive outcomes of small incision lenticule extraction for the correction of myopia: 1-year follow-up

OBJECTIVE

To assess the 1 year clinical outcomes of small incision lenticule extraction (SMILE) for the correction of myopia and myopic astigmatism using a 500 kHz femtosecond laser system.

METHODS

This prospective study evaluated 52 eyes of 39 consecutive patients (31.8±6.9 years, mean age±SD) with spherical equivalents of -4.11±1.73 D (range, -1.25 to -8.25 D) who underwent SMILE for myopia and myopic astigmatism. Preoperatively, 1 week, and 1, 3, 6 and 12 months postoperatively, we assessed the safety, efficacy, predictability, stability, corneal endothelial cell loss and the adverse events of the surgery.

RESULTS

The logarithm of the minimal angle of resolution (logMAR) uncorrected distance visual acuity and LogMAR corrected distance visual acuity were -0.16±0.11 and -0.22±0.07, respectively, 1 year postoperatively. At 1 year, all eyes were within±0.5 D of the targeted correction. Manifest refraction changes of -0.05±0.32 D occurred from 1 week to 1 year postoperatively (p=0.20, Wilcoxon signed-rank test). The endothelial cell density was not significantly changed from 2804±267 cells/mm(2) preoperatively to 2743±308 cells/mm(2) 1 year postoperatively (p=0.12). No vision-threatening complications occurred during the observation period.

CONCLUSIONS

SMILE performed well in the correction of myopia and myopic astigmatism, and no significant change in endothelial cell density or any other serious complications occurred throughout the 1-year follow-up period, suggesting its viability as a surgical option for the treatment of such eyes.

Refractive lenticule extraction: transition and comparison of 3 surgical techniques

PURPOSE

To describe the transition and outcomes of 3 refractive lenticule extraction (ReLEx) techniques: femtosecond lenticule extraction (FLEx), small-incision lenticule extraction (SMILE), and pseudo small-incision lenticule extraction.

SETTING

Singapore National Eye Center, Singapore.

DESIGN

Prospective comparative case series.

METHODS

Refractive lenticule extraction was performed between March 1, 2010, and November 1, 2012, using the Visumax 500 kHz femtosecond laser system. The main outcome measures were the refractive efficacy, predictability, and safety over 12 months.

RESULTS

The study enrolled 88 eyes. All 3 refractive lenticule extraction techniques yielded good refractive outcomes and stability over 12 months. Three months postoperatively, the mean overall efficacy index of refractive lenticule extraction was 0.89±0.22 (SD), with 95.5% of eyes attaining an uncorrected distance visual acuity (UDVA) of better than 20/40 and 60.2% of better than 20/20. Of all eyes, 95.5% were within ±1.00 diopter (D) and 78.4% within ±0.50 D of the attempted correction. The mean overall safety index was 1.06±0.17. At 3 months, all small-incision lenticule extraction eyes and 96.7% of pseudo small-incision lenticule extraction eyes had a UDVA of 20/40 or better, while femtosecond lenticule extraction eyes had a lower efficacy index (87.0%). However, efficacy was comparable in all 3 groups by 12 months (mean 0.87±0.04 [standard error of the mean]; P=1.00).

CONCLUSION

The efficacy, safety, and predictability profiles of the 3 refractive lenticule extraction techniques were good over a 12-month follow-up.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Anterior and Posterior Corneal Astigmatism after Refractive Lenticule Extraction for Myopic Astigmatism

Purpose. To assess the amount and the axis orientation of anterior and posterior corneal astigmatism after refractive lenticule extraction (ReLEx) for myopic astigmatism. Methods. We retrospectively examined 53 eyes of 53 consecutive patients (mean age ± standard deviation, 33.2 ± 6.5 years) undergoing ReLEx to correct myopic astigmatism (manifest cylinder = 0.5 diopters (D)). Power vector analysis was performed with anterior and posterior corneal astigmatism measured with a rotating Scheimpflug system (Pentacam HR, Oculus) and refractive astigmatism preoperatively and 3 months postoperatively. Results. Anterior corneal astigmatism was significantly decreased, measuring 1.42 ± 0.73 diopters (D) preoperatively and 1.11 ± 0.53 D postoperatively (p < 0.001, Wilcoxon signed-rank test). Posterior corneal astigmatism showed no significant change, falling from 0.44 ± 0.12 D preoperatively to 0.42 ± 0.13 D postoperatively (p = 0.18). Refractive astigmatism decreased significantly, from 0.92 ± 0.51 D preoperatively to 0.27 ± 0.44 D postoperatively (p < 0.001). The anterior surface showed with-the-rule astigmatism in 51 eyes (96%) preoperatively and 48 eyes (91%) postoperatively. By contrast, the posterior surface showed against-the-rule astigmatism in all eyes preoperatively and postoperatively. Conclusions. The surgical effects were largely attributed to the astigmatic correction of the anterior corneal surface. Posterior corneal astigmatism remained unchanged even after ReLEx for myopic astigmatism.

Effect of femtosecond laser setting on visual performance after small-incision lenticule extraction for myopia

AIM

To compare the effect of the two femtosecond laser settings on visual performance after small-incision lenticule extraction (SMILE) for myopia and myopic astigmatism.

METHODS

Forty-four eyes of 22 consecutive patients who underwent SMILE with an energy level of 140 nJ (spot distance 3.0 µm) in one eye, and with an energy level of 170 nJ (spot distance 4.5 µm) in the other eye, the eyes being randomly assigned. Preoperatively, 1 week, and 1 and 3 months postoperatively, the values of the modulation transfer function (MTF) cutoff frequency, Strehl ratio, objective scattering index (OSI) and Optical Quality Analysis System (OQAS) values (OVs) for these eyes were quantitatively assessed using an Optical Quality Analysis System (Visiometrics).

RESULTS

No significant differences were detected between the two groups in the visual and refractive outcomes, or in the MTF cutoff frequency, the Strehl ratio, the OSI, the OV 100%, the OV 20% or the OV 9% at any time point before or after surgery.

CONCLUSIONS

SMILE with energy settings of 140 and 170 nJ was effective for the correction of myopia and myopic astigmatism. It is indicated that the differences in laser setting (140 nJ, spot distance 3.0 µm vs 170 nJ, spot distance 4.5 µm) did not significantly affect the optical quality including the intraocular scattering of eyes undergoing SMILE.

CLINICAL TRIAL NUMBER

The protocol was registered with University Hospital Medical Information Network Clinical Trial Registry (UMIN000016241).

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

Purpose

To compare postoperative astigmatic correction between femtosecond lenticule extraction (FLEx) and small-incision lenticule extraction (SMILE) in eyes with myopic astigmatism.

Methods

We examined 26 eyes of 26 patients undergoing FLEx and 26 eyes of 26 patients undergoing SMILE to correct myopic astigmatism (manifest astigmatism of 1 diopter (D) or more). Visual acuity, cylindrical refraction, the predictability of the astigmatic correction, and the astigmatic vector components using Alpin’s method, were compared between the two groups 3 months postoperatively.

Results

We found no statistically significant difference in manifest cylindrical refraction (p=0.74) or in the percentage of eyes within ± 0.50 D of their refraction (p=0.47) after the two surgical procedures. Moreover, no statistically significant difference was detected between the groups in astigmatic vector components, namely, surgically induced astigmatism (0.80), target induced astigmatism (p=0.87), astigmatic correction index (p=0.77), angle of error (p=0.24), difference vector (p=0.76), index of success (p=0.91), flattening effect (p=0.79), and flattening index (p=0.84).

Conclusions

Both FLEx and SMILE procedures are essentially equivalent in correcting myopic astigmatism using vector analysis, suggesting that the lifting or non-lifting of the flap does not significantly affect astigmatic outcomes after these surgical procedures.

Small-incision lenticule extraction for myopia: results of a 12-month prospective study

PURPOSE

To analyze the safety, efficacy, stability, and predictability of small-incision lenticule extraction to correct myopia.

METHODS

Patients were evaluated preoperatively and then at 1 day, at 2 weeks, and at 1, 3, 6, and 12 months postoperatively. Safety, efficacy, stability, predictability, and surgical complications were assessed. Changes in higher-order aberrations, intraocular pressure, central corneal thickness, dry eye signs, contrast sensitivity, and subjective glare symptoms were evaluated.

RESULTS

All 52 myopic patients in the initial treatment group completed the final 12-month follow-up. At 12 months, 90.4% of eyes were within ±0.5 diopters (D) of the intended refractive target. The mean (±SD) change in manifest refraction from 1 day to 12 months was -0.06 (±0.37) D. The uncorrected visual acuity was better than or equal to 20/20 in 83% of eyes; 98% of eyes had a best-corrected visual acuity of better than or equal to 20/20. No eye lost two or more Snellen lines. There was an increase in higher-order aberrations, spherical aberration, and coma postoperatively. No significant increase in intraocular pressure occurred. The tear breakup time decreased significantly after surgery and did not return to preoperative levels within 12 months. The log contrast sensitivity value with glare of 6.3, 4.0, 2.5, and 1.6 degrees of visual angle at 1 month was statistically significantly reduced but recovered to preoperative levels after 3 months. Twenty-seven percent of patients complained of mild or moderate glare postoperatively, but the symptoms disappeared during the 12-month follow-up period with no influence on daily life. No vision-threatening complications occurred.

CONCLUSION

Small-incision lenticule extraction is a promising corneal refractive procedure to correct myopia.

Comparison of astigmatic correction after femtosecond lenticule extraction and wavefront-guided LASIK for myopic astigmatism

PURPOSE

To compare postoperative astigmatic correction between femtosecond lenticule extraction (FLEx) and wavefront-guided LASIK in eyes with myopic astigmatism.

METHODS

Fifty-eight eyes of 41 patients undergoing FLEx and 49 eyes of 29 patients undergoing wavefront-guided LASIK to correct myopic astigmatism were examined. Visual acuity, cylindrical refraction, predictability of the astigmatic correction, and astigmatic vector components were compared between groups 6 months after surgery.

RESULTS

There was no statistically significant difference in manifest cylindrical refraction (P = .08) or percentage of eyes within ± 0.50 diopter (D) of its refraction (P = .11) between the surgical procedures. The index of success in FLEx was statistically significantly better than that of wavefront-guided LASIK (P = .02), although there was no significant difference between the groups in other indices (eg, surgically induced astigmatism, target-induced astigmatism, astigmatic correction index, angle of error, difference vector, and flattening index). Subgroup analysis showed that FLEx had a better index of success (P = .02) and difference vector (P = .04) than wavefront-guided LASIK in the low cylinder subgroup; the angle of error in FLEx was significantly smaller than that of wavefront-guided LASIK in the moderate cylinder subgroup (P = .03).

CONCLUSIONS

Both FLEx and wavefront-guided LASIK worked well for the correction of myopic astigmatism by the 6-month follow-up visit. Although FLEx had a better index of success than wavefront-guided LASIK when using vector analysis, it appears equivalent to wavefront-guided LASIK in terms of visual acuity and the correction of astigmatism.

Early changes in ocular surface and tear inflammatory mediators after small-incision lenticule extraction and femtosecond laser-assisted laser in situ keratomileusis

PURPOSE

To characterize the early ocular-surface changes or tear inflammatory-mediators levels following small-incision lenticule extraction (ReLEx smile) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK).

METHODS

Forty-seven myopic subjects were recruited for this prospective study. Fifteen underwent ReLEx smile and thirty-two underwent FS-LASIK. Corneal fluorescein (FL) staining, tear break-up time (TBUT), Schirmer I test (SIT), ocular surface disease index (OSDI) and central corneal sensitivity were evaluated in all participants. Tears were collected and analyzed for interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), nerve growth factor (NGF) and intercellular adhesion molecule-1 (ICAM-1) levels using multiplex magnetic beads. All measurements were preformed preoperatively and 1 day, 1 week, 1 month and 3 months postoperatively.

RESULTS

FL scores in ReLEx smile group were lower than those of FS-LASIK group 1 week postoperatively (P = 0.010). Compared to the FS-LASIK group, longer TBUT were observed in ReLEx smile group 1 month (P = 0.029) and 3 months (P = 0.045) postoperatively. No significant differences were found in tear secretion for the two groups (P>0.05). OSDI scores were higher in FS-LASIK group 1 month after surgery (P = 0.020). Higher central corneal sensitivity was observed in ReLEx smile group 1 week, 1 month and 3 months (P<0.05) postoperatively. Compared to FS-LASIK group, lower and faster recovery of IL-6 and NGF levels in tears was observed in ReLEx smile group postoperatively (P<0.05). Tears TNF-α and ICAM-1 concentrations were not significantly different between the two groups at any follow-up time (P>0.05). Moreover, IL-6 and NGF levels correlated with ocular surface changes after ReLEx smile or FS-LASIK.

CONCLUSIONS

In the early postoperative period, ReLEx smile results in milder ocular surface changes than FS-LASIK. Furthermore, the tear inflammatory mediators IL-6 and NGF may play a crucial role in the ocular surface healing process following ReLEx smile and FS-LASIK.

Comparative study of corneal endothelial cell damage after femtosecond laser assisted deep stromal dissection

Purpose. To find a relatively safe designed stromal bed thickness to avoid endothelial damage for lamellar keratoplasty with an Allegretto Wavelight FS200 femtosecond laser. Methods. Twelve rabbits were randomly divided into 50 μm and 150 μm groups according to the anticipated residue stromal bed thickness preparation with a femtosecond laser. Six rabbits without laser cutting were used as a control group. Central endothelial images were analyzed with in vivo confocal microscopy and scanning electron microscopy. The apoptosis of endothelium was evaluated with Hoechst 33342 staining and a TUNEL assay. Results. The endothelium of the 50 μm group had extensive injuries upon in vivo confocal and scanning electron microscopic observation, and minor injuries were observed in the 150 μm group. Moreover, more apoptotic cells were observed in the 50 μm group. Conclusions. When using a FS200 femtosecond laser assisted anterior lamellar keratoplasty, there was minor endothelium damage with a 150 μm stromal bed, and a more than 150 μm thickness stromal bed design may prevent the damage of corneal endothelium.

Developments in the correction of presbyopia II: surgical approaches

PURPOSE

To discuss the various static and dynamic surgical approaches which attempt to give presbyopes good vision at far, intermediate and near viewing distances.

CONTENT

Static methods broadly adopt the same optical techniques as those used in presbyopic contact lens correction and aim to satisfy the needs of the presbyope by increasing binocular depth-of-focus, often using monovision as well as simultaneous-imagery. Dynamic methods generally attempt to make use of at least some of the still-active elements of the accommodation system. They include procedures which are supposed to modify the relative geometry of the ciliary muscle and lens, or which reduce the stiffness of the presbyopic lens either by replacing it with other natural or man-made material or by subjecting it to femtosecond laser treatment. Alternatively the natural lens may be replaced by some form of intraocular lens which changes power as a result of forces derived from the still-active ciliary muscle, zonule and capsule, or other sources.

CONCLUSIONS

At present, multifocal intraocular lenses appear to offer the most consistent and reliable surgical approach to surgical presbyopic correction. They have obvious advantages in convenience and stability over optically-similar, simultaneous-image presbyopic contact lenses but this must be balanced against their relative inflexibility in cases of patient dissatisfaction. Dynamic methods remain largely experimental. Although some approaches show promise, as yet no method has demonstrated a reliable, long-term ability to correct distance refractive error and to appropriately change ocular power in response to changes in viewing distance over the normal range of interest.

Comparison of visual acuity and higher-order aberrations after femtosecond lenticule extraction and small-incision lenticule extraction

PURPOSE

To compare postoperative visual acuity and higher-order aberrations (HOAs) after femtosecond lenticule extraction (FLEX) and after small-incision lenticule extraction (SMILE).

METHODS

Medical records of refractive lenticule extraction patients were retrospectively reviewed. Twenty patients were treated with FLEX. A comparable group of 20 SMILE patients were retrospectively identified. Only one eye of each patient was randomly chosen for the study. Visual acuity, subjective manifest refraction and corneal topography before and 6 months after the surgery were analyzed for both groups. Total HOAs, spherical aberrations, coma and trefoil were calculated from topography data over the 4- and 6-mm-diameter central corneal zone.

RESULTS

The mean preoperative SE was -4.03 ± 1.61 in the SMILE group and -4.46 ± 1.61 in the FLEX group. One year after surgery, the mean SE was -0.33 ± 0.25 in the SMILE group and -0.31 ± 0.41 in the FLEX group (p=0.86). In the SMILE group a greater number of eyes were within ±0.50D of the target refraction (95% versus 75%); however, the difference was not statistically significant (p=0.18). Furthermore, 80% of FLEX eyes and 95% of SMILE eyes had an uncorrected distance visual acuity of 20/25 or better (p=0.34). Total HOAs, spherical aberration, coma and trefoil increased postoperatively in both groups. However, there was no statistically significant difference between the groups preoperatively and postoperatively.

CONCLUSION

FLEX and SMILE result in comparable refractive results. In addition, corneal aberrations induced by different techniques of lenticule extraction seemed similar to each other.

Past and present of corneal refractive surgery: a retrospective study of long-term results after photorefractive keratectomy and a prospective study of refractive lenticule extraction

Surgical correction of refractive errors is becoming increasingly popular. In the 1990s, the excimer laser revolutionized the field of corneal refractive surgery with PRK and LASIK, and lately refractive lenticule extraction (ReLEx) of intracorneal tissue, using only a femtosecond laser, has become possible. Two new procedures were developed, ReLEx flex (FLEX) and ReLEx smile (SMILE). Until this thesis, only a few long-term studies of PRK with a relatively limited number of patients had been published; therefore, this thesis intended to retrospectively evaluate long-term outcomes after PRK for all degrees of myopia for a large number of patients. Furthermore, a prospective contralateral eye study comparing FLEX and SMILE, when treating high to moderate degrees of myopia, had not been performed prior to this study. This was the second aim of this thesis. In the first study, results from 160 PRK patients (289 eyes) were presented. Preoperative spherical equivalent ranged from -1.25 to -20.25 D, with 78% having low myopia (<-6 D). Average follow-up time was 16 years (range 13-19 years), making this the longest published follow-up study on PRK patients. Outcomes from eyes with low myopia were generally superior to outcomes from eyes with high myopia, at final follow-up. Seventy-two percent were within ± 1.00 D of target refraction, as compared to 47% of eyes with high myopia. However, results from a subgroup of unilateral treated PRK patients indicated that refraction at final follow-up was affected by myopic progression. Fifty percent of eyes with low myopia had uncorrected 20/20 distance visual acuity or better, as compared to 22% of eyes with high myopia. Haze did not occur if attempted corrections were <-4 D, and only eyes with high myopia lost two lines or more of CDVA (corrected distance visual acuity). Eighty-one per cent were satisfied or very satisfied with their surgery.

CONCLUSION

The results support the continued use of the excimer laser for corneal surface ablation as a treatment option for correction of low degrees of myopia, and as the treatment of choice for subgroups of refractive patients (thin corneas, etc.). The results also highlight that treatment of higher degrees of myopia with standard PRK should only be done today under special circumstances, due to low refractive predictability, and high risk of corneal haze. Technological advances since then should be taken into account when comparing these results with contemporary techniques. In the second study, 35 patients were randomized to receive FLEX in one eye and SMILE in the other. Preoperative spherical equivalent refraction ranged from -6 to -10 D with low degrees of astigmatism. A total of 34 patients completed the 6 month follow-up period. Refractive and visual outcomes were very similar for the two methods, as well as tear film measurements and changes in corneal biomechanics. Ninety-seven percent were within ± 1.00 D of target refraction, no eyes lost two lines or more of CDVA, and contrast sensitivity was unaffected after both procedures. The changes in higher-order aberrations were also very similar. There were also no differences in tear film parameters 6 months after surgery, although less postoperative foreign body sensation was reported within the first week after surgery in SMILE eyes. Corneal sublayer pachymetry measurements demonstrated equally increased epithelial thickness 6 months after surgery. Contrary to expectations, it was not possible to measure the theoretical biomechanical advantages of a small corneal incision in SMILE as compared to a corneal flap in FLEX. The main differences between FLEX and SMILE were found when the corneal nerves and intraoperative complications were evaluated. Thus, corneal sensitivity was better preserved and corneal nerve morphology was less affected after SMILE, but intraoperative complications occurred more frequently, although without visual sequela. Finally, 97% were satisfied or very satisfied with both their surgeries.

CONCLUSION

The results support the continued use of both FLEX and SMILE for treatment of up to high degrees of myopia. Overall, refractive and visual results for both procedures were good and similar, but from a biological point of view, the less invasive SMILE technique is more attractive, as demonstrated in this study, despite being slightly more surgically demanding than FLEX.

Visual and refractive outcomes of femtosecond lenticule extraction and small-incision lenticule extraction for myopia

PURPOSE

To compare the visual and refractive outcomes of femtosecond lenticule extraction (FLEx) and small-incision lenticule extraction (SMILE) in eyes with myopia.

DESIGN

Prospective, randomized, masked clinical trial with intraindividual comparison.

METHODS

This study evaluated 52 eyes of 26 consecutive patients with spherical equivalents of -4.19 ± 1.65 diopters (D) (mean ± standard deviation) who underwent FLEx in 1 eye and SMILE in the other eye by randomized assignment. Before surgery, and 1 week and 1, 3, and 6 months after surgery, we assessed safety, efficacy, predictability, stability, and adverse events of the 2 surgical techniques.

RESULTS

LogMAR uncorrected and corrected distance visual acuity was, respectively, -0.17 ± 0.10, -0.20 ± 0.07 in the FLEx group and -0.15 ± 0.10, -0.19 ± 0.07 in the SMILE group 6 months postoperatively. In the FLEx and SMILE groups 6 months postoperatively, 96% and 100% of eyes, respectively, were within 0.5 D of the targeted spherical equivalent correction. Changes of -0.02 ± 0.39 D and 0.00 ± 0.30 D occurred in manifest refraction from 1 week to 6 months in the FLEx and SMILE groups, respectively. No clinically significant complications occurred in the FLEx or the SMILE group.

CONCLUSIONS

Both FLEx and SMILE performed well in the correction of myopia throughout the 6-month observation period. FLEx may be essentially equivalent to SMILE in terms of safety, efficacy, predictability, and stability, suggesting that the presence or absence of lifting the flap does not significantly affect these visual and refractive outcomes.

Time course of optical quality and intraocular scattering after refractive lenticule extraction

Purpose

To assess the time course of optical quality and intraocular scattering in relation to visual acuity after femtosecond lenticule extraction (FLEx) for the correction of myopia.

Methods

This study evaluated 36 eyes of 36 patients with spherical equivalents of −4.38±1.53 D [mean ± standard deviation] who underwent FLEx. Before surgery, and 1 week and 1, 3 and 6 months after surgery, we assessed the modulation transfer function (MTF) cutoff frequency, Strehl ratio, objective scattering index (OSI), and OQAS values (OVs), using a double-pass instrument. We also investigated the relationship of the OSI with corrected distance visual acuity (CDVA) preoperatively and postoperatively.

Results

The mean changes in MTF cutoff frequency, Strehl ratio, OSI, OV100%, OV20%, and OV9% preoperatively and 6 months postoperatively were −5.51±15.01, −0.03±0.07, 0.35±0.83, −0.17±0.48, −0.14±0.38, and −0.09±0.22, respectively. We found no significant preoperative correlation between the OSI and logMAR CDVA (Spearman rank correlation coefficient r = 0.068, p = 0.69), and modest, but significant correlations 1 week and 1, 3, and 6 months postoperatively (r = 0.572, r = 0.562, r = 0.542, r = 0.540, p<0.001, respectively).

Conclusions

FLEx induced a transient decrease in optical quality in association with an increase in intraocular scattering in the early postoperative period, possibly due to mild interface haze formation, but gradually recovered with time. It is suggested that this transient degradation in optical quality related to an increase in the intraocular scattering may result in a slight delay of CDVA recovery in the early postoperative period.