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Epithelial thickness profile map: absolute difference between 6 months postoperatively and baseline (mean 6 SD).
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Purpose:
To assess the reactive changes of the corneal epithelial thickness (ET) profile induced by small incision lenticule extraction (SMILE) for treatment of myopia.
Methods:
This prospective observational study included 46 eyes of 23 patients that were scheduled for myopic SMILE. High-resolution spectral-domain optical coherence tomography (...
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Background
To investigate corneal higher-order aberrations (HOAs) of the anterior surface, posterior surface, and total cornea after small incision lenticule extraction (SMILE) in high myopic and mild to moderate myopic patients.
Methods
This retrospective study included 197 eyes (101 patients) undergoing SMILE surgery. According to the preoperati...
Purpose
To evaluate femtosecond laser in flap and cap creation, detect some corneal biomechanical changes, and evaluate dry eye after laser in situ keratomileusis (LASIK), Femto-LASIK, and small incision lenticule extraction (SMILE) with 3-year follow-up.
Patients and methods
Preoperative evaluation taken: full ophthalmic examination, Pentacam, oc...
This study was aimed to evaluate refractive and visual outcomes after micro-monovision small incision lenticule extraction (SMILE) in patients with presbyopia and myopia. In total, 72 patients (144 eyes) with a mean age of 46.0 ± 4.9 years were included in this study. The dominant eye was treated for distance vision and the nondominant eye for near...
Objective
To investigate the influence of creating a flap on the postoperative optical quality of the cornea in terms of predicted corneal curvature and Seidel aberrations after 2 modalities of femtosecond assisted corneal lenticule extraction laser for the correction of myopia and myopic astigmatism: the flapless procedure small incision lenticula...
AimTo compare postoperative clinical outcomes of high myopia after small-incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK).Methods
From March 2018 to July 2020, PubMed, MEDLINE, Embase, the Cochrane Library, and several Chinese databases were comprehensively searched. The studies meeting th...
Citations
... SMILE has advantages of lesser dry eye symptoms and early recovery after procedure as it is less damaging to corneal tissue with minimal nerve disruption. The smaller incision maintains biomechanical stability and corneal strength [3]. But, the procedure is mainly applicable in myopia particularly high myopia, leaving behind the patients of far-sightedness and astigmatism, though, with time its treatment range is expanding [4]. ...
SMILE has advantages of lesser dry eye symptoms and early recovery after procedure as it is less damaging to corneal tissue with minimal nerve disruption. The smaller incision maintains biomechanical stability and corneal strength [3]. But, the procedure is mainly applicable in myopia particularly high myopia, leaving behind the patients of far-sightedness and astigmatism, though, with time its treatment range is expanding [4]. The main disadvantage is its inapplicability in patients with higher-order aberrations and the hypermetropia patients. The surgeon needs to perform a requisite number of SMILE surgeries before producing perfect results with minimal complications [5]. Previous studies have shown that SMILE surgery has better
... Previous studies have shown that epithelial hyperplasia in different areas of the cornea after surgery may be related to intended spherical equivalent (SE) correction, optical zone diameter, and other factors. [10][11][12] However, the relationship between corneal epithelial remodeling and postoperative refractive changes remains controversial among studies, [12][13][14][15] and the specific mechanism requires further study. ...
... Previous studies have reported the pattern of corneal epithelial remodeling after various surgeries, such as PRK, LASIK, and SMILE. 11,13,16,17 Our previous studies have also reported an asymmetric lenticule-like pattern of epithelial remodeling occurring in a 9-mm corneal diameter after SMILE. 11,14 However, to our knowledge, no study has reported the corneal epithelial remodeling in patients who underwent surface ablation retreatment after SMILE. ...
Purpose
To assess changes in corneal epithelial thickness (ET) within 9-mm diameter cornea after photorefractive keratectomy (PRK) retreatment after small-incision lenticule extraction (SMILE).
Methods
A total of 28 eyes of 19 patients with mean spherical equivalent of −1.30 ± 0.60 D who underwent retreatment after SMILE were included in this retrospective study. ET mapped across a 9-mm diameter area was obtained using wide-field optical coherence tomography (OCT) before and at one, three, and six months after surgery. The ET changes were compared between the different time points and analyzed zones.
Results
Before enhancement, the ET were 63.64 ± 6.01 µm and 61.25 ± 4.32 µm in central and paracentral zones, respectively. The ET of central and paracentral zones significantly decreased at one month and subsequently increased until six months. Six months after surgery, significant epithelial thickening occurred in 2- to 9-mm diameter cornea (all P < 0.05), whereas no significant change was observed in central 2-mm diameter cornea (P = 0.460). There was no significant difference in the ET between the central and paracentral zones (P = 1.00). The degree of myopic correction significantly correlated with the average ET in the central (P = 0.046) and paracentral (P = 0.033) zones at six months after PRK enhancement. No significant correlation was detected between the average ET of all zones and the postoperative spherical equivalent at six months after surgery (all P > 0.05).
Conclusions
PRK enhancement did not alter the overall trend of corneal epithelial remodeling induced by SMILE. An asymmetric and flatter lenticule-like pattern of epithelial remodeling was observed six months after surgery, which did not affect the refractive outcomes.
Translational Relevance
An asymmetric and centrally flattened lenticule-like pattern of epithelial remodeling was observed after PRK enhancement. Surgeons should consider expanding the intended optical zones for enhancement surgery after SMILE.
... Many previous studies [5][6][7] have reported increased epithelial thickness (ET) following corneal refraction surgery, similarly, there are several studies [8][9][10][11][12][13][14] on corneal epithelial changes after SMILE. However, there have been no studies evaluated corneal epithelial remodeling patterns following the combined SMILE and prophylactic CXL (SMILE-xtra). ...
... The sample size was determined to have a power of at least 80% based on existing published results using MedCalc software (version 22.013, MedCalc Software Ltd., Ostende, Belgium) [8][9][10][11][12][13][14]. Data were analyzed using SPSS, version 24.0 (IBM Corporation, Armonk, NY, USA), for Windows (Corporation, Redmond, WA, USA). ...
... Therefore, there is less possibility of affecting the corneal limbal epithelial stem cells, and it is thought that it will act more on the stromal side to induce effective collagen cross-linking [29]. In this study, the mean ET of the central 2 mm increased by 4.15 μm of SMILE group and 3.90 μm of SMILE-xtra group in six months postoperatively, which was relatively small compared to previous studies [9][10][11]. The discrepancy may be due to the different measuring instruments [30] and the different preoperative SE and race [31] of the participants. ...
Purpose
To evaluate the changes of the corneal epithelial thickness (ET) profile induced by combined small incision lenticule extraction and accelerated corneal collagen crosslinking (SMILE-xtra) for myopia compared with the standard small incision lenticule extraction (SMILE).
Setting
Nuri Eye Hospital, 61, Dunsan-ro, Seo-gu, Daejeon, 35233, Korea.
Design
Retrospective cross-sectional study.
Methods
Thirty-one myopic eye undergoing SMILE-xtra and control group of 36 myopic eyes undergoing SMILE were retrospectively analyzed. Spectral-domain optical coherence tomography (CIRRUS™ HD-OCT 5000, ZEISS, Dublin, CA) was used to measure corneal ET of 17 zones within the central 7-mm zone at preoperative, postoperative 1 month, 3 months and 6 months. Postoperative ET alterations were analyzed for correlation with treatment parameters.
Results
There was no difference in preoperative mean age, postoperative MRSE, visual acuity, and ablation depth between the two groups, and there was a significant difference in preoperative central corneal thickness. Both groups showed the greatest increase in corneal ET in the paracentral area on the inferotemporal area, respectively, for 6 months. The preoperative MRSE and the ablation depth showed significant correlation with the postoperative epithelial thickening in mid-peripheral sectors in both groups, and significant negative correlations in paracentral sectors only in SMILE-xtra group.
Conclusions
It is significant as the first study to compare corneal epithelial remodeling between SMILE and SMILE with accelerated corneal collagen crosslinking. The SMILE-xtra with the relatively large corneal ablation did not show a significant difference in the pattern of corneal epithelial remodeling compared to the SMILE group.
... Moreover, previous studies on corneal epithelial thickness after SMILE found that the anterior corneal surface sagged and the corneal stroma showed morphological and structural changes due to lens removal, which induced the corneal epithelium to form a regular and smooth corneal surface through the compensatory mechanism to maintain normal optical function, so that the corneal epithelium is continuously hyperplasia and remodeling like a convex lens. The reconstructive process tended to be stable at 3 months postoperatively [30], which could explain a rebound in Km and an increase in CCT within 3 months after SMILE. At the same time, the compensation mechanism was more significant in patients with high myopia and high astigmatism [31,32], thus the changes in Km and CT are more obvious in the high myopia group compared to the moderate myopia group. ...
Purpose
To evaluate the early corneal remodeling and its influencing factors after Small incision lenticule extraction (SMILE) for moderate and high myopia.
Methods
This was a retrospective study. Pre- and post-operative (1 week and 1, 3, 6 months) corneal volume (CV), mean keratometry (Km), and corneal thickness (CT) were measured by Scheimpflug tomography. CT at the central, thinnest point, and on concentric circles of 2, 4, and 6 mm diameter was recorded to assess corneal thickness spatial profile (CTSP) and percentage of thickness increase (PTI) in the moderate and high myopia groups, and to explore possible influencing factors.
Results
After SMILE, the peripheral CT decreased in the moderate myopia group and central corneal thickness (CCT) increased in the high myopia group at 1 month compared to 1 week (all P < 0.05). The CV, Km and CT were significantly increased at 3 months compared to 1 month (all P < 0.05), but there was no significant change at 6 months compared to 3 months for both groups (all P > 0.05). Patients with high myopia showed greater corneal thickness changes (△CT) and higher PTI than moderate myopia (all P < 0.05). Regression analysis revealed that in addition to refraction, peripheral PTI was negatively correlated with CCT in the moderate myopia group (4 mm: β = -0.023, P = 0.001; 6 mm: β = -0.050, P < 0.001), as well as in the high myopia group (4 mm: β = -0.038, P < 0.001; 6 mm: β = -0.094, P < 0.001). Moreover, peripheral PTI in the moderate myopia group was negatively correlated with age (4 mm: β = -0.071, P = 0.003; 6 mm: β = -0.162, P < 0.001).
Conclusions
After SMILE, the CV, Km, and CTSP showed dynamic changes in the early stage, which stabilized after 3 months. Compared to the moderate myopia group, the high myopia group experienced slower corneal stabilization. The change in PTI at 6 months after SMILE may be related to higher preoperative refraction, thinner CCT and younger age.
... Corneal epithelial remodeling may contribute to the CCT changes after corneal refractive surgery. Nikolaus Luft et al. reported that significant epithelial thickening was observed after SMILE, FS-LASIK, and PRK [11]. In a study of corneal epithelial remodeling over 2 years in SMILE and LASIK, Kanellopoulos et al. revealed that the eyes showed an epithelial thickness increase in the first 12 months after SMILE and LASIK, with a stronger thickening trend in the first 3 months [12]. ...
To compare the central corneal thickness (CCT) treated with small incision lenticule extraction (SMILE), femtosecond laser-assisted in situ keratomileusis (FS-LASIK), or laser-assisted subepithelial keratomileusis (LASEK) for myopia correction. This was a retrospective case series study. Patients who had completed 1-year follow-up after receiving SMILE, FS-LASIK, or LASEK at our hospital from January 2019 to July 2021 were included. Pentacam pachymetry was performed to measure the CCT. The predicted CCT reduction was obtained through laser platform. The measured CCT reduction was defined as the difference between the preoperative and postoperative CCT using Pentacam pachymetry. There were 100 eyes treated by SMILE, 100 eyes by FS-LASIK, and 100 eyes by LASEK. There was a significant difference in predicted CCT reduction among the three surgeries (P < 0.001), but no significant difference in measured CCT reduction postoperatively (PGroup = 0.373). At 1 year postoperatively, the CCT reduction was overestimated by 17.85 ± 5.36 µm in the SMILE group, underestimated by 4.31 ± 7.08 µm in the FS-LASIK group, and underestimated by 7.60 ± 8.28 µm in the LASEK group (PGroup < 0.001, PTime < 0.001). In the FS-LASIK group, the difference between predicted and measured CCT reduction was not related to the predicted CCT reduction (P = 0.095). The laser platform may overestimate the CCT reduction for SMILE and underestimate it for FS-LASIK and LASEK. FS-LASIK has a much higher level of accuracy in CCT reduction, which is not influenced by refractive correction.
... [6][7][8][9] It has been postulated that regression rates may be lower following SMILE vis-à-vis LASIK secondary to milder stromal healing response and lesser epithelial remodeling postoperatively. [10] However, the published data thus far is exceedingly limited. ...
Purpose:
To compare visual outcomes of early enhancement following small incision lenticule extraction (SMILE) versus laser in situ keratomileusis (LASIK).
Methods:
Retrospective analysis of eyes (patients operated in the setting of a tertiary eye care hospital between 2014 and 2020) requiring early enhancement (within one year of primary surgery) was conducted. Stability of refractive error, corneal tomography, and anterior segment Optical Coherence Tomography (AS-OCT) for epithelial thickness was performed. The correction post regression was done using photorefractive keratectomy and flap lift in eyes, wherein the primary procedure was SMILE and LASIK, respectively. Pre- and post enhancement corrected and uncorrected distance visual acuity (CDVA and UDVA), mean refractive spherical equivalent (MRSE), and cylinder were analyzed. IBM SPSS statistical software.
Results:
In total, 6350 and 8176 eyes post SMILE and LASIK, respectively, were analyzed. Of these, 32 eyes of 26 patients (0.5%) post SMILE and 36 eyes of 32 patients (0.44%) post-LASIK required enhancement. Post enhancement (flap lift in LASIK, and PRK in SMILE group) UDVA was logMAR 0.02 ± 0.05 and 0.09 ± 0.16 (P = 0.009), respectively. There was no significant difference between the refractive sphere (P = 0.33) and MRSE (P = 0.09). In total, 62.5% of the eyes in the SMILE group and 80.5% in the LASIK group had a UDVA of 20/20 or better (P = 0.04).
Conclusion:
PRK post SMILE demonstrated comparable results to flap lift post LASIK and is a safe and effective approach for early enhancement post SMILE.
... 1,2 This compensation activity, called epithelial remodeling, has been observed after keratoconus, 3 keratoplasty, cataract surgery, 4 corneal cross-linking, 5 and refractive surgery. [6][7][8] Previous studies showed that epithelial remodeling ABSTRACT PURPOSE: To investigate corneal epithelial thickness changes during a 6-month follow-up period after transepithelial photorefractive keratectomy (tPRK), femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK), and small incision lenticule extraction (SMILE). ...
... There are currently three common and relatively safe myopia-correction refractive surgery procedures: femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK), small incision lenticule extraction (SMILE), and transepithelial photorefractive keratectomy (tPRK). 12 Earlier studies found that the epithelium thickened to varying degrees after FS-LASIK, 11 SMILE, 8,13 and tPRK, 7,14 but assessment of that change was limited to the central 6-mm diameter region and did not include comparisons between the three surgeries. A comparative study that considers epithelial thickness changes over a larger region may help in applications including the selection of surgical methods and parameters. ...
... 24 Similarly, earlier data suggested that epithelial remodeling stabilized following SMILE 3 months postoperatively. 8 However, corneal epithelial thickness after myopic LASIK showed a progressive epithelial thinning from 1 to 6 months of follow-up in Díaz-Bernal's study. 25 As for tPRK, continuous epithelial hyperplasia was observed within 6 months in this study, which was consistent with Shetty et al's study 14 and different from Chen et al's 7 observation of epithelial stability from pos3m to pos6m. ...
Purpose:
To investigate corneal epithelial thickness changes during a 6-month follow-up period after transepithelial photorefractive keratectomy (tPRK), femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK), and small incision lenticule extraction (SMILE).
Methods:
This prospective study included 76 eyes of 76 participants who underwent myopic refractive surgery (23 FS-LASIK, 22 SMILE, and 31 tPRK). Epithelial thickness and anterior curvature were averaged over 4 regions (subdivided into 25 areas) and measured by spectral-domain optical coherence tomography and Scheimpflug tomography before the operation (pre) and at 1 or 3 days (pos1-3d), 1 week (pos1w), and 1 month (pos1m), 3 months (pos3m), and 6 months (pos6m) postoperatively.
Results:
The epithelial thickness of the three groups was similar in both the pre and pos6m (all P > .05), but the tPRK group fluctuated the most during the follow-up period. The largest increase was in the inferior-temporal paracentral area (7.25 ± 2.58 μm for FS-LASIK; 5.79 ± 2.41 μm for SMILE; 4.88 ± 5.84 μm for tPRK; all P < .001). Only the epithelial thickness of tPRK increased from pos3m to pos6m (P < .05), whereas all changes for FS-LASIK and SMILE were not significant (P > .05). A positive correlation of thickness changes with curvature gradient in the paracentral region of tPRK was found (r = 0.549, P = .018), but not in other regions in all groups.
Conclusions:
Epithelial remodeling followed different trends after different surgeries from the early postoperative stage onward, but exhibited similar values at pos6m. Although remodeling after FS-LASIK and SMILE stabilized by pos3m, it remained unstable at pos6m after tPRK. These changes may affect corneal profile and lead to deviation from the intended surgical outcome. [J Refract Surg. 2023;39(3):187-196.].
... Data on corneal epithelial thickness (CET) changes after LVC procedures are limited [25]. Luft et al observed a 10% thickening of the corneal epithelium in the first 180 days after surgery [25]. ...
... Data on corneal epithelial thickness (CET) changes after LVC procedures are limited [25]. Luft et al observed a 10% thickening of the corneal epithelium in the first 180 days after surgery [25]. They reported that the changes that stabilized 90 days after surgery were related to the preoperative size of the visual defect [25]. ...
... Luft et al observed a 10% thickening of the corneal epithelium in the first 180 days after surgery [25]. They reported that the changes that stabilized 90 days after surgery were related to the preoperative size of the visual defect [25]. They also showed that the regenerative potential of the corneal epithelium decreases with age [25]. ...
Background
This study from a single center in Poland included 120 patients with myopia, and the aim was to compare vision correction and corneal thickness at the 180-day follow-up after femtosecond laser-assisted in-situ keratomileusis (FS-LASIK), photorefractive keratectomy (PRK), or small incision lenticule extraction (SMILE).
Material/Methods
The effectiveness and safety of laser vision correction (LVC) procedures were evaluated by determining pre- and post-procedure uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA) values on the Snell chart. Twenty patients with diagnosed mild myopia (sphere maximum −3.0 diopters D; cylinder maximum 0.5 D) were qualified for PRK surgery. Fifty patients with diagnosed intolerance (sphere maximum −6.0 D; cylinder maximum 5.0 D) were eligible for the FS-LASIK procedure. Fifty patients with diagnosed myopia (sphere maximum −6.0 D cylinder 3.5 D) were qualified for the SMILE procedure.
Results
Regardless of which procedure was performed, both UDVA and CDVA improved significantly postoperatively (P<0.05). In addition, the UDVA and CDVA values were similar in the postoperative period (P>0.05). For each procedure, the EI was no less than 0.94. Regardless of which type of LVC procedure was performed, CET at the center and 1.5 mm from the center in 4 meridians thickened, and this change was not statistically significant over the observation period (P>0.05).
Conclusions
Our analysis demonstrated similar effectiveness of the 3 methods – PRK, FS-LASIK, and SMILE – in patients with mild and moderate myopia.
... However, the exact mechanism underlying the postoperative HOAs changes always deserves further in-depth studies. After FS-LASIK or SMILE surgeries, significant epithelial thickening was observed [14,25,26]. Ryu et al. found actual corneal stromal layer was about 11.9 μm thicker than predicted at 3 months after SMILE [27]. ...
Purpose
The aim of this study is to evaluate morphological features of corneal flap/cap and the correlations with corneal higher-order aberrations (HOAs) changes after femtosecond laser in situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE).
Methods
This was a retrospective study. Pre- and postoperative (1 and 3 months) corneal HOAs were assessed with Pentacam HR. The corneal flap/cap thickness at 32 points (± 1.5 mm, ± 2 mm, ± 2.5 mm, and ± 3 mm from the corneal vertex on meridian 0°/45°/90°/135°) were measured using anterior segment optical coherence tomography at 3 months postoperatively. Morphological features of corneal flap/cap including predictability (P), uniformity (U), and symmetry (S) were calculated and used for correlation analysis with corneal HOAs changes.
Results
Eighty-six eyes (44 patients) and ninety-six eyes (50 patients) were involved in FS-LASIK and SMILE groups, respectively. Significant thicker corneal flap/cap than the predicted was observed at each measuring point and meridian in both groups (difference > 2.225 μm, the within-subject standard deviation over 6-mm optical zone). There was no statistically significant difference in predictability of corneal flap/cap thickness, while U6 mm (P < .0001), U0 (P < .001), U45 (P = .002), U90 (P < .0001), U135 (P = .004), S6 mm (P < .0001), S0 (P < .001), and S90 (P < .0001) over 6 mm zone were less in SMILE than in FS-LASIK. The changes of corneal tHOAs, Z (3, − 1), Z (3, 1), and SA were significantly correlated with morphological features of corneal flap/cap.
Conclusion
Both FS-LASIK and SMILE had good predictability in flap or cap thickness, while the uniformity and symmetry of SMILE cap were better than FS-LASIK flap. The quality of flap/cap was closely associated with the changes of corneal HOAs.
... Meanwhile, non-contact anterior segment optical coherence tomography (AS-OCT) provides a fast high-resolution method for studying these changes with reliable repeatability indices. [3][4][5] With the emergence of new commercial AS-OCT technologies, corneal parameters can be measured with higher quality and precision. In this scenario, the hybrid AS-OCT with an incorporated Placido disc corneal topographer (MS-39; CSO) allows a precise analysis of the changes produced in the cornea at the epithelial and stromal levels. ...
PURPOSE
To evaluate the postoperative changes in corneal epithelium thickness and refractive power after femtosecond laser–assisted laser in situ keratomileusis (LASIK) and small incision lenticule extraction (SMILE) for myopia correction using anterior segment optical coherence tomography (OCT) with an integrated Placido disc topographer.
METHODS
The VisuMax 500-kHz femtosecond laser (Carl Zeiss Meditec AG) and Amaris 750 excimer laser (SCHWIND eye-tech-solutions) were used. Central, paracentral, and 6-mm epithelial thickness values were obtained, and the change in the value of epithelial thickness was calculated. Changes in the refractive power of the epithelium were also evaluated. The repeatability of this new measurement was also analyzed using the intraclass correlation (ICC). The total follow-up period was 6 months.
RESULTS
A total of 77 LASIK eyes were matched with 77 SMILE eyes. Mean spherical equivalent was −3.92 ± 1.67 diopters (D) for LASIK versus −4.02 ± 1.63 D for SMILE ( P = .356). Epithelial thickness parameters significantly and equally thickened in both types of surgery. The change in the value of epithelial thickness was positively correlated with spherical aberration. Analysis of the refractive power of the corneal epithelial layer (ICC > 0.70) showed a tendency for the postoperative myopization of the refractive component of this layer (−0.11 D for SMILE and −0.53 D for LASIK at 3 mm) and an increase in its cylinder and aberrometry. Increasing postoperative spherical aberration and epithelial thickness increased myopization of the epithelial refractive sphere ( P < .05).
CONCLUSIONS
Corneal epithelium thickens similarly after LASIK and SMILE, being slightly higher after SMILE. This correlates with the induced spherical aberration. Corneal epithelium thickening induces myopization of its refractive power, which accounts for a slight regression of the net refractive power change on the treated cornea.
[ J Refract Surg . 2022;38(9):602–608.]
