A Three-Year Observation of Corneal Backscatter After Small Incision Lenticule Extraction (SMILE)

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Characterization the corneal transparency profile in SMILE-treated myopic patients with densitometry: A 7-year cohort study

PURPOSE

To investigate 7-year changes in corneal densitometry (CD) and its influencing factors following small incision lenticule extraction (SMILE) for moderate to high myopia.

METHODS

A total of 32 patients (52 eyes) with a mean spherical equivalent (SE) refraction of -6.30 ± 1.30 D who underwent SMILE were recruited for this prospective study. Pre- and postoperative CD and corneal aberrations were measured by an oculus Pentacam system, and patients were followed up to 7 years. The CD evolution over time and its influencing factors were explored.

RESULTS

No complications were observed after SMILE. There was a significant time effect on postoperative CD ( P < 0.05). The CD values at the 0-to-2 and 2-to-6 mm of the anterior layer increased at the first day ( P < 0.05) and declined to baselines at 1 year postoperatively; after that, CD values at any zone and any corneal layer presented a decreasing trend over time (all P < 0.05). Multivariate analysis showed that postoperative CD was positively correlated with age and optical zone (OZ), whereas negatively correlated with SE, corrected distance visual acuity (CDVA), and corneal aberrations (higher-order aberrations, Coma0 and Coma90) (all P < 0.05). Generalized estimating equation revealed that age, SE, CDVA, OZ, and Coma0 were the main factors influencing postoperative CD values (all P < 0.05).

CONCLUSION

CD manifested a long-term decreasing trend in moderate to high myopia treated with SMILE. Its main influencing factors are age, SE, CDVA, OZ, and Coma0.

Visual outcomes and corneal densitometry after allogenic and autologous lenticule intrastromal keratoplasty for the correction of moderate-to-high hyperopia

AIM

This study aimed to evaluate the visual outcomes and corneal densitometry (CD) after allogenic lenticule intrastromal keratoplasty (AL-LIKE) and autologous lenticule intrastromal keratoplasty (AU-LIKE) for the correction of moderate-to-high hyperopia.

METHODS

Ten subjects (14 eyes) underwent AL-LIKE and eight (8 eyes) underwent AU-LIKE. Patients were examined preoperatively and 1 day, 1 month, and 6 months postoperatively. The visual outcomes and CD for both surgical methods were evaluated.

RESULTS

No postoperative complications were observed with either method. The efficacy index was 0.85±0.18 and 0.90±0.33 in the AL-LIKE and AU-LIKE groups, respectively. The safety indices were 1.07±0.21 and 1.25±0.37 in the AL-LIKE and AU-LIKE groups, respectively. The CD values of the anterior, central, and posterior layers in the AL-LIKE group increased significantly at 1 day postoperatively (all P < 0.05). The CD values of the anterior and central layers remained significantly higher than the preoperative values at 6 months postoperatively (all P < 0.05). The CD values of the anterior layer in the AU-LIKE group increased significantly 1 day postoperatively (all P < 0.05) and decreased to preoperative values (all P > 0.05) 1 month postoperatively.

CONCLUSION

Both AL-LIKE and AU-LIKE exhibit good efficacy and safety in correcting hyperopia. However, AU-LIKE may have a smaller affected area and faster recovery time than those associated with AU-LIKE related to changes in corneal transparency.

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.

Corneal optical density: Structural basis, measurements, influencing factors, and roles in refractive surgery

The cornea is the main refractive medium of the human eye, and its clarity is critical to visual acuity. Corneal optical density (COD) is an important index to describe corneal transparency. Intact corneal epithelial and endothelial cells, regular arrangement of collagen fibers in the stroma, and normal substance metabolism are all integral for the cornea to maintain its transparency. In the last two decades, the Pentacam Scheimpflug imaging system has emerged as a breakthrough for the measurement of COD (also called corneal densitometry). It has been found that a wide variety of factors such as age, refractive status, and corneal diseases can affect COD. Different corneal refractive surgery methods also change COD in different corneal regions and layers and affect visual acuity following the surgery. Thus, COD has gradually become a significant indicator to evaluate corneal health, one on which the attention of clinicians has been increasingly focused.

Long-term changes in corneal densitometry and associated factors following small incision lenticule extraction for moderate and high myopia

Purpose

To investigate long-term trends in corneal densitometry and associated influencing factors following small incision lenticule extraction (SMILE).

Methods

A comparative study was performed among 72 eyes of 38 patients undergoing SMILE. Eyes were divided into moderate myopia [mean spherical equivalent (SE),−4.22 ± 0.68D] and high myopia (mean SE,−7.63 ± 1.09 D) groups. Visual acuity, manifest refraction, corneal topography and corneal densitometry (CD) were evaluated preoperatively and 3 years postoperatively.

Results

The efficacy indices at last postoperative follow-up (42.47 ± 0.51 months) were 0.92 ± 0.21 and 0.97 ± 0.22, the safety indices were 1.12 ± 0.17 and 1.14 ± 0.21 for high and moderate myopia, respectively (all P > 0.05). CD values in the 0–6 mm zone of the posterior corneal layer was statistically significantly lower than the preoperative values in both groups. Postoperative CD values (0–2 mm zone) in the posterior layer of the high myopia group were statistically significantly lower than in the moderate myopia group (P = 0.025); CD values (2–6 mm zone) in the anterior layer were higher in the high myopia group (P = 0.026). Correlation analyses showed that CD values in the 0–2 mm middle layer were negatively correlated with lenticule thickness in high myopia (r = −0.411, P = 0.016); there was a negative correlation between the CD values (0–6 mm) and corneal oblique trefoil in this group (P < 0.05).

Conclusion

Corneal transparency in the 0–6 mm zone of the posterior cornea increased following SMILE in moderate and high myopia. Long-term CD values in high myopia may be correlated with oblique trefoil and lenticule thickness.

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.

Nighttime Symptoms After Monocular SMILE: A Contralateral Eye Study

Introduction

To investigate nighttime symptoms in patients with myopic anisometropia after monocular small incision lenticule extraction (SMILE) surgery.

Methods

Thirty-six patients who had undergone monocular SMILE more than 6 months previously were recruited at the Eye & ENT Hospital of Fudan University. The average age at surgery was 25.4 ± 6.1 years. Preoperative spherical equivalent (SE) was −3.77 ± 1.56 D in SMILE-treated eyes and −0.08 ± 0.66 D in unoperated eyes. Main measurements included uncorrected and corrected distance visual acuity, manifest refraction, halo radius, contrast sensitivity, nighttime symptoms, and patient satisfaction.

Results

The mean follow-up time was 13.9 ± 3.4 months. The efficacy and safety indexes were 1.18 and 1.28, respectively. The halo radius was not significantly different between SMILE-treated and unoperated eyes under luminance conditions of 1, 5, and 100 cd/m² (P = 0.055). No significant differences were observed in contrast sensitivity at all spatial frequencies between eyes under both uncorrected and corrected conditions (all P > 0.05). None of the patients reported moderate or severe symptoms at night. Mild symptoms (glare, halo, starburst) were reported and binocularly equal in 13 patients, whereas four patients reported better night vision in SMILE-treated eyes than unoperated eyes, and one of them experienced mild night vision disturbance. The overall satisfaction score was 9.39 ± 0.80.

Conclusions

The disk halo size and contrast sensitivity in SMILE-treated eyes were similar to those in unoperated eyes, and nighttime symptoms almost completely resolved after SMILE.

One-step viscoelastic agent technique for ICL V4c implantation for myopia

AIM

To investigate the safety and efficacy of using a one-step viscoelastic agent technique for posterior chamber phakic implantable collamer lens with a central hole (ICL V4c) implantation for myopia correction.

METHODS

The one-step viscoelastic agent technique for ICL V4c implantation was used in 100 eyes of 52 patients. Refractive outcomes, intraocular pressure (IOP), corneal endothelial cell, and corneal densitometry values were evaluated at 1d, 1wk, 1 and 3mo postoperatively.

RESULTS

All the surgeries were uneventful. No corrected distance visual acuity was lost after 3mo. IOP was 16.12±3.18 mm Hg before surgery, and 14.74±3.08 mm Hg at 1d and 14.50±2.56 mm Hg at 3mo after surgery (P<0.05). Corneal endothelial cell density was 2580±242 cell/mm², the coefficient of variation in cell size was 42.11%±7.92%, and the percentage of hexagonal cells was 40.98%±9.46% before surgery. No significant difference was found when these outcomes were compared between the studied time points (P>0.05). The corneal densitometry values of the central 2 mm and 2 to 6 mm areas showed similar regularities. After surgery, the values significantly increased at 1d, then decreased to the preoperative values at 1wk, and then continued to decrease at 3mo (P<0.05).

CONCLUSION

The one-step viscoelastic agent technique for ICL V4c implantation is found to be safe and effective for myopia correction and causes little disturbance to the cornea.

Corneal Densitometry After Small Incision Lenticule Extraction (SMILE) and Femtosecond Laser-Assisted LASIK (FS-LASIK): 5-Year Prospective Comparative Study

Purpose: To investigate long-term changes in corneal densitometry (CD) following small incision lenticule extraction (SMILE) vs. femtosecond laser-assisted LASIK (FS-LASIK) in patients with myopia or myopic astigmatism.

Methods: Prospective analysis was performed in 66 eyes of 38 patients (13 males) who underwent SMILE and 54 eyes of 29 patients (5 males) who underwent FS-LASIK. In all patients, an ocular examination was performed preoperatively, and at 6–12 months and 5 years postoperatively. CD was obtained with the Pentacam Scheimpflug imaging system at the 0–2-mm, 2–6-mm, and 6–10-mm zones of the cornea at depth of anterior 120 μm, midcornea, and posterior 60 μm. Correlation analysis was performed between postoperative change in CD and other variables such as age, type of surgery, central corneal thickness, spherical equivalent, lenticule thickness/ablation depth, and changes in wavefront aberrations.

Results: At postoperative 6–12 months, a significant reduction at several corneal zones in the FS-LASIK cohort (P < 0.05) was observed. In the SMILE cohort, no significant change in CD relative to baseline was observed. However, at 5 years postoperatively, in both groups, a significant decrease in CD was observed in three zones of three layers (all P < 0.001). The change in CD was similar between groups at postoperative 6–12 months, but at 5 years the magnitude of change was significantly smaller in SMILE than FS-LASIK in the anterior and central layers (all P < 0.05).

Conclusion: CD with the Scheimpflug imaging system showed a significant decrease at 5 years after SMILE or FS-LASIK, and the change was significantly less pronounced after SMILE.

Evaluation of disk halo size after small incision lenticule extraction (SMILE)

PURPOSE

To investigate changes in objective disk halo size produced by a glare source after small incision lenticule extraction (SMILE) for myopia correction.

METHODS

This prospective clinical study included 45 right eyes of 45 patients with a mean age of 25.40 ± 5.06 years and mean spherical equivalent (SE) of - 6.08 ± 1.90 diopters. Disk halo size was measured with a vision monitor before surgery and at postoperative 1 week and 3 months. Other information was collected, including age, SE, lenticule thickness, lenticule diameter, dark pupil, and pupillary response to light parameters (initial diameter; amplitude, latency, duration, and velocity of contraction; latency, duration, and velocity of dilation; and maximum, minimum, and average pupil size).

RESULTS

Compared to preoperative values, disk halo size increased significantly at postoperative 1 week (P = 0.026) and returned to baseline at postoperative 3 months (P = 0.349). Preoperative disk halo size significantly correlated with SE (r = - 0.346, P = 0.020), minimum pupil size (r = 0.365, P = 0.014), and average pupil size (r = 0.310, P = 0.038). Disk halo size at postoperative 1 week was significantly correlated with age (r = 0.324, P = 0.030) and minimum pupil size (r = 0.297, P = 0.047). Disk halo size at postoperative 3 months was significantly correlated with lenticule diameter (r = - 0.362, P = 0.015), initial diameter (r = 0.311, P = 0.037), maximum pupil size (r = 0.312, P = 0.037), minimum pupil size (r = 0.440, P = 0.002), and average pupil size (r = 0.373, P = 0.012).

CONCLUSIONS

After SMILE, disk halo size demonstrated a temporary increase and then returned to baseline.

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

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

Visual and refractive outcomes of 100 small incision lenticule extractions (SMILE) in moderate and high myopia: a 24-month follow-up study

PURPOSE

We aimed to present the visual results obtained in 100 small incision lenticule extraction (SMILE) refractive surgeries, demonstrate whether the technique is effective in the treatment of moderate and high myopia, and observe the follow-up of these patients over 24-month period.

METHODS

One hundred eyes of 50 consecutive patients were treated with SMILE. The preoperative spherical equivalent refraction was - 5.64 ± 1.23 D. During the postoperative period, patients were examined at 3, 6, 12, and 24 months. We analysed the efficacy, safety, predictability, and stability of the technique.

RESULTS

The Snellen visual acuity of 99% of the patients was 20/20 or better after 24 months of follow-up. Two eyes had a loss of two lines of visual acuity; 1% of the patients had a loss of one line of visual acuity. The postoperative spherical refraction was - 0.04 ± 0.35 D (- 1.00 to 0.50 D). The postoperative spherical equivalent refraction was - 0.19 ± 0.38 D (- 1.25 to 0.50 D). Eighty-three percent of the eyes were within ± 0.50 D, and 87% obtained a residual astigmatism of 0.50 D or less.

CONCLUSION

The SMILE technique was demonstrated to be an effective, predictable, safe, and stable technique in the treatment of moderate-to-severe myopia during the 24-month follow-up. Long-term follow-up should be undertaken to observe possible refractive regressions.

Intraoperative Patient Experience and Postoperative Visual Quality After SMILE and LASIK in a Randomized, Paired-Eye, Controlled Study

PURPOSE

To compare intraoperative and postoperative subjective patient experience after small incision lenticule extraction (SMILE) and femtosecond laser-assisted LASIK.

METHODS

In a prospective, randomized, paired-eye, single-masked clinical trial at Singapore National Eye Centre, 70 patients were randomly treated with SMILE and LASIK in each eye. The intraoperative questionnaire was completed immediately after surgery and included light perception and levels of anxiety, fear, and discomfort. The postoperative 1- and 3-month questionnaires evaluated severity of light sensitivity, eye discomfort, eye dryness, excessive tearing, gritty sensation, glare, halos, blurring, and fluctuations in vision.

RESULTS

Average discomfort scores were higher during tissue manipulation in SMILE (1.9 ± 0.9) than flap lifting in LASIK (1.59 ± 0.8) (P = .020) but comparable during docking and laser application (P > .249). Fear scores were lower in SMILE than LASIK during docking (2.6 ± 1.6 vs 3.4 ± 1.9, P = .024) but similar during occasional blackout, laser application, and lenticule/flap manipulation (P > .364). Fear scores were generally higher in patients with intraoperative suction loss (n = 3). For SMILE, light sensitivity, eye discomfort, blurring, and fluctuations in vision improved from 1 to 3 months (P < .039). For LASIK, improvements were reported for light sensitivity, eye discomfort, eye dryness, gritty sensation, and fluctuations in vision from 1 to 3 months (P < .046). At 1 month, patients experienced more blurring after SMILE than LASIK (2.1 ± 0.8 vs 1.8 ± 0.7, P = .025), but with no differences in any of the visual symptoms at 3 months.

CONCLUSIONS

Tissue manipulation may be more uncomfortable during SMILE than LASIK, but not more frightening. Subjective visual symptoms were comparable after 3 months. [J Refract Surg. 2018;34(2):92-99.].

Short-term Observation of Intraocular Scattering and Bowman's Layer Microdistortions After SMILE-CCL

PURPOSE

To investigate changes in intraocular scattering and Bowman's layer microdistortions after femtosecond laser small incision lenticule extraction using the continuous curvilinear lenticulerhexis technique (SMILE-CCL).

METHODS

In this prospective study, 93 eyes of 93 patients (44 women, 49 men) were treated with SMILE-CCL. Mean age was 26.09 ± 4.39 years and mean spherical equivalent was -6.31 ± 2.16 diopters. The Objective Scatter Index (OSI) was examined with an objective optical quality analysis system. Bowman's layer microdistortions in the central 4-mm optical zone were measured using Fourier-domain optical coherence tomography.

RESULTS

The mean OSI value increased from 0.67 preoperatively to 1.09 at 20 days, and then decreased to 0.84 at 3 months (P < .05). Microdistortions were observed in 62.37% of the eyes at 20 days and 48.39% at 3 months postoperatively (P < .05). The width of the microdistortions per meridian was 283.18 ± 197.19 μm at 20 days; this decreased to 156.00 ± 159.86 μm at 3 months (P < 0.05). Regression analysis models revealed that older age (b = 0.02, P = .03) and higher preoperative spherical equivalent (b = -0.09, P < .05) resulted in higher postoperative OSI values; no significant association was found between postoperative OSI values and microdistortion-related parameters (P > .05). Higher preoperative spherical equivalent (b = -0.28, P = .01) and thinner preoperative corneal thickness (b = -0.02, P = .01) were associated with more microdistortions.

CONCLUSIONS

SMILE induced a temporary increase in OSI values and Bowman's layer microdistortions. The microdistortions did not influence intraocular scattering. [J Refract Surg. 2018;34(6):387-392.].