Meiyan Li

Comparison of Dry Eye and Corneal Sensitivity between Small Incision Lenticule Extraction and Femtosecond LASIK for Myopia

Purpose To investigate the changes in dry eye symptoms and clinical signs and corneal sensitivity after small incision lenticule extraction (SMILE) and femtosecond LASIK (femto-LASIK). Design Prospective, non-randomized comparative study. Methods The study included a total of 71 eyes of 71 patients; the SMILE group comprised 38 eyes of 38 patients, and the femto-LASIK group comprised 33 eyes of 33 patients. Ocular Surface Disease Index (OSDI), Tear film breakup time (TBUT), the Schirmer test without anesthesia (S1T), corneal fluorescein staining, and central corneal sensation were evaluated before surgery and at 1 week, 1 month, 3 months, and 6 months after surgery. Results OSDI scores in both groups were increased immediately and returned to preoperative level at 1 month after surgeries. The TBUT values in both groups were reduced after surgeries relative to their preoperative scores. Patients in SMILE group were less likely to have corneal staining compared with those in the femto-LASIK group ([odds ratio] OR = 0.50, 95% [confidence interval] CI 0.28 to 0.93, P = 0.03). Central corneal sensitivity was decreased at all postoperative time points in both groups. However, the central corneal sensation scores in the SMILE group were greater than that in the femto-LASIK group at all of the postoperative time points (all P<0.05). Conclusions SMILE surgeries resulted in a short-term increase in dry eye symptoms, tear film instability, and loss of corneal sensitivity. Furthermore, SMILE surgeries have superiority over femto-LASIK in lower risk of postoperative corneal staining and less reduction of corneal sensation.

Comparison of corneal deformation parameters after SMILE, LASEK, and femtosecond laser-assisted LASIK.

PURPOSE To investigate the differences in corneal deformation parameters after femtosecond laser small incision lenticule extraction (SMILE), laser-assisted subepithelial keratomileusis (LASEK), and femtosecond laser-assisted LASIK (FS-LASIK). METHODS In this retrospective study, 17 eyes of 17 patients after SMILE, 18 eyes of 18 patients after LASEK, and 17 eyes of 17 patients after FS-LASIK were included. Corneal deformation parameters were measured with the CorVis ST tonometer (Oculus Optikgeräte GmbH, Wetzlar, Germany) 3 months postoperatively. RESULTS The mean value of deformation amplitude of the FS-LASIK group was significantly higher than that of the LASEK group (P = .022). The mean value of applanation time (applanation 1) of the LASEK group was significantly higher than that of the FS-LASIK group (P = .038). No significant difference was detected in the mean values of deformation amplitude and applanation time (applanation 1) (P > .05) between the LASEK and SMILE groups or between the SMILE and FS-LASIK groups. Multiple linear regression model analysis revealed that after adjustment for age and preoperative central corneal thickness and manifest refraction spherical equivalent, the significance of the difference in the mean values of applanation time (applanation 1) and deformation amplitude between the LASEK and FS-LASIK groups were P = .084 and .059, respectively. In all three groups, the values of applanation 1 negatively correlated to those of applanation time (applanation 2) (SMILE: r = −0.577, P = .015; LASEK: r = −0.833, P < .001; FS-LASIK: r = −0.516, P = .034) and deformation amplitude (SMILE: r = −0. 556, P = .021; LASEK: r = −0.877, P < .001; FS-LASIK: r = −0.509, P = .037). CONCLUSIONS Applanation time (applanation 1) and deformation amplitude (as measured with the CorVis ST tonometer) may be helpful in assessing corneal biomechanical changes after corneal refractive surgery. The relations between these parameters should be discussed in further studies.

Confocal Comparison of Corneal Reinnervation after Small Incision Lenticule Extraction (SMILE) and Femtosecond Laser In Situ Keratomileusis (FS-LASIK)

Purpose To evaluate corneal reinnervation, and the corresponding corneal sensitivity and keratocyte density after small incision lenticule extraction (SMILE) and femtosecond laser in situ keratomileusis (FS-LASIK). Methods In this prospective, non-randomized observational study, 18 patients (32 eyes) received SMILE surgery, and 22 patients (42 eyes) received FS-LASIK surgery to correct myopia. The corneal subbasal nerve density and microscopic morphological changes in corneal architecture were evaluated by confocal microscopy prior to surgery and at 1 week, 1 month, 3 months, and 6 months after surgery. A correlation analysis was performed between subbasal corneal nerve density and the corresponding keratocyte density and corneal sensitivity. Results The decrease in subbasal nerve density was less severe in SMILE-treated eyes than in FS-LASIK-treated eyes at 1 week (P = 0.0147), 1 month (P = 0.0243), and 3 months (P = 0.0498), but no difference was detected at the 6-month visit (P = 0.5277). The subbasal nerve density correlated positively with central corneal sensitivity in both groups (r = 0.416, P<0.0001, and r = 0.2567, P = 0.0038 for SMILE group and FS-LASIK group, respectively). The SMILE-treated eyes have a lower risk of developing peripheral empty space with epithelial cells filling in (P = 0.0005). Conclusions The decrease in subbasal nerve fiber density was less severe in the SMILE group than the FS-LASIK group in the first 3 months following the surgeries. The subbasal nerve density was correlated with central corneal sensitivity.

Microdistortions in Bowman's layer following femtosecond laser small incision lenticule extraction observed by Fourier-Domain OCT.

PURPOSE To study microdistortions in Bowmans layer after femtosecond laser small incision lenticule extraction (SMILE) using Fourier-domain optical coherence tomography (OCT) and to investigate possible sources and potential visual impacts. METHODS A nonrandomized controlled prospective study enrolled 52 eyes of 29 consecutive patients undergoing SMILE, with spherical equivalent of -6.33 ± 1.88 diopters and 4.2 mm superior incision. The microdistortions in Bowmans layer were counted at 1 day, 1 week, and 1 month postoperatively and at long-term follow-up. Another 38 eyes of 20 patients undergoing femtosecond laser-assisted LASIK (FS-LASIK) were examined at 1 day and long-term postoperatively as the control group. RESULTS Microdistortions in Bowmans layer were observed by OCT, with no clinically significant corneal striae under slit-lamp microscopy, in 46 eyes (88.5%) on day 1 after SMILE and in 16 eyes (42.1%) after FS-LASIK, with more in SMILE eyes than in FS-LASIK eyes. The amount decreased at 1 week and then remained stable. There were more microdistortions in the center area than in the periphery in both groups. Microdistortions were more in the inferior than the superior quadrant on the first day after SMILE but there was no difference at long-term follow-up. Microdistortions after SMILE were associated with the refractive lenticule thickness and surgery order but had no significant impact on long-term visual outcomes or wavefront aberrations. CONCLUSIONS Microdistortions in Bowmans layer after SMILE were associated with the refractive lenticule thickness and surgery order. The microdistortions remained stable after 1 week and had no impact on long-term visual performance. [J Refract Surg. 20XX;XX(X):XX-XX].PURPOSE To study microdistortions in Bowmans layer after femtosecond laser small incision lenticule extraction (SMILE) using Fourier-domain optical coherence tomography (OCT) and to investigate possible sources and potential visual impacts. METHODS A nonrandomized controlled prospective study enrolled 52 eyes of 29 consecutive patients undergoing SMILE, with spherical equivalent of -6.33 ± 1.88 diopters and 4.2 mm superior incision. The microdistortions in Bowman’s layer were counted at 1 day, 1 week, and 1 month postoperatively and at long-term follow-up. Another 38 eyes of 20 patients undergoing femtosecond laser-assisted LASIK (FS-LASIK) were examined at 1 day and long-term postoperatively as the control group. RESULTS Microdistortions in Bowman’s layer were observed by OCT, with no clinically significant corneal striae under slit-lamp microscopy, in 46 eyes (88.5%) on day 1 after SMILE and in 16 eyes (42.1%) after FS-LASIK, with more in SMILE eyes than in FS-LASIK eyes. The amount decreased at 1 week and then remained stable. There were more microdistortions in the center area than in the periphery in both groups. Microdistortions were more in the inferior than the superior quadrant on the first day after SMILE but there was no difference at long-term follow-up. Microdistortions after SMILE were associated with the refractive lenticule thickness and surgery order but had no significant impact on long-term visual outcomes or wavefront aberrations. CONCLUSIONS Microdistortions in Bowmans layer after SMILE were associated with the refractive lenticule thickness and surgery order. The microdistortions remained stable after 1 week and had no impact on long-term visual performance.

Mild decentration measured by a Scheimpflug camera and its impact on visual quality following SMILE in the early learning curve.

PURPOSE To measure decentration following femtosecond laser small incision lenticule extraction (SMILE) for the correction of myopia and myopic astigmatism in the early learning curve, and to investigate its impact on visual quality. METHODS A total of 55 consecutive patients (100 eyes) who underwent the SMILE procedure were included. Decentration was measured using a Scheimpflug camera 6 months after surgery. Uncorrected and corrected distance visual acuity (UDVA, CDVA), manifest refraction, and wavefront errors were also measured. Associations between decentration and the preoperative spherical equivalent were analyzed, as well as the associations between decentration and wavefront aberrations. RESULTS Regarding efficacy and safety, 40 eyes (40%) had an unchanged CDVA; 32 eyes (32%) gained one line; and 11 eyes (11%) gained two lines. Fifteen eyes (15%) lost one line of CDVA, and two eyes (2%) lost two lines. Ninety-nine of the treated eyes (99%) had a postoperative UDVA better than 1.0, and 100 eyes (100%) had a UDVA better than 0.8. The mean decentered displacement was 0.17 ± 0.09 mm. The decentered displacement of all treated eyes (100%) was within 0.50 mm; 70 eyes (70%) were within 0.20 mm; and 90 eyes (90%) were within 0.30 mm. The vertical coma showed the greatest increase in magnitude. The magnitude of horizontal decentration was found to be associated with an induced horizontal coma. CONCLUSIONS This study suggests that, although mild decentration occurred in the early learning curve, good visual outcomes were achieved after the SMILE surgery. Special efforts to minimize induced vertical coma are necessary.

Comparison of corneal sensation between small incision lenticule extraction (SMILE) and femtosecond laser-assisted LASIK for myopia.

PURPOSE To compare the impact on corneal sensation after small incision lenticule extraction (SMILE) and femtosecond laser-assisted LASIK (femto-LASIK) in patients with myopia. METHODS In this prospective, nonrandomized comparative study, 71 subjects were enrolled. Thirty-eight eyes of 38 patients underwent SMILE and 33 eyes of 33 patients underwent femto-LASIK. Corneal sensation was tested with Cochet-Bonnet esthesiometry in five corneal areas preoperatively and at 1 week and 1, 3, and 6 months postoperatively. Comparison of corneal sensation was performed for the SMILE and femto-LASIK groups. Additionally, the correlations were evaluated between the postoperative corneal sensation, preoperative spherical equivalent, and ablation depth. RESULTS All tested areas within the cap or flap demonstrated corneal hypoesthesia immediately after both surgeries. SMILE-treated eyes showed less compromised corneal sensation than femto-LASIK-treated eyes at all postoperative visits in the central, inferior, nasal, and temporal areas at the 1-week and 1-month visits. In the SMILE group, the inferior, nasal, and temporal quadrants recovered faster than other areas. In the femto-LASIK group, the sensation over the flap did not recover to preoperative levels by postoperative 6 months. There was no correlation between postoperative corneal sensation, preoperative spherical equivalent, and ablation depth in both groups. CONCLUSIONS The impairment of corneal sensation was less significant in the SMILE group than in the femto-LASIK group and was independent of preoperative spherical equivalent or ablation depth.

The Morphology of Corneal Cap and Its Relation to Refractive Outcomes in Femtosecond Laser Small Incision Lenticule Extraction (SMILE) with Anterior Segment Optical Coherence Tomography Observation

Purpose To investigate the morphology of corneal caps in femtosecond laser small incision lenticule extraction (SMILE) and its relation to the refractive outcomes. Methods A prospective study of fifty-four corneal caps created with VisuMax femtosecond laser were examined using an Fourier-domain optical coherence tomography at 1 day, 1 week, 1 month and 6 months after SMILE. The cap thickness at nine points on each of the four meridians (0°, 45°, 90°, 135°) and the diameter were measured. Cap morphology, changes over time and its correlation with refractive outcomes were assessed. Results The mean achieved central cap thickness were (108.74±5.06) µm at 6 months and (107.32±4.81 ) µm at 1 month postoperatively, significantly thinner than that at 1 day (110.81±7.95) µm and 1 week (109.58±7.48 ) µm (P<0.05). The mean diameter on 0° meridian was (7.61±0.07) mm, significantly larger than that on 90° meridian (7.57±0.06) mm (P = 0.001). Cap morphology showed good regularity, except that the differences of points in two pairs were significant at 1 day postoperatively. The uniformity was consistent over time and the central cap thickness was thinner than those in the paracentral and peripheral areas. The refractive outcomes stabilized within 1 month. Uncorrected distance visual acuity (UDVA) was correlated to the central cap thickness at 1 day and 1 week (both rs = 0.33, p<0.05). The uniformity index was correlated with UDVA (rs = 0.34, p<0.05) and corrected distance visual acuity (rs = 0.32, p<0.05) at 1 week postoperatively. Conclusions Corneal caps of SMILE are predictable with good reproducibility, regularity and uniformity. Cap morphology might have a mild effect on refractive outcomes in the early stage. Further study should focus on the impact on the visual quality.

The Safety and Predictability of Implanting Autologous Lenticule Obtained by SMILE for Hyperopia

PURPOSE To evaluate the safety, effectiveness, stability, and predictability of implanting autologous lenticules obtained from small incision lenticule extraction for the treatment of hyperopia. METHODS Five patients (10 eyes) with one myopic eye and one hyperopic eye were enrolled. The myopic eye was treated with small incision lenticule extraction; a lenticule was extracted and subsequently implanted in the hyperopic eye. Follow-up was at 1 day, 1, 3, 6, and 9 months, and 1 year postoperatively. Patients received a complete ophthalmologic examination at each visit, including uncorrected distance visual acuity, corrected distance visual acuity, anterior segment optical coherence tomography, and corneal topography. RESULTS There were no complications in any eye during follow-up. Compared with preoperative levels, at the last follow-up visit the eyes with lenticule implantation showed mean spherical equivalent reduced by 5.53 diopters (residual spherical equivalent was +1.13 to -2.63 diopters), mean uncorrected distance visual acuity increased approximately two lines (approximately 20/63 to 20/40 Snellen), and corrected distance visual acuity in 4 (80%) eyes gained one line, 2 (40%) eyes gained two lines, and 1 (20%) eye gained more than two lines. There was no significant difference (P > .05) in spherical equivalent compared with 1 day postoperatively and the last follow-up visit. Corneal topography showed that the lenticule was uniform and located well; anterior segment optical coherence tomography images showed that the lenticule was transparent and the demarcation line was visible. CONCLUSIONS Implanting an autologous lenticule obtained by small incision lenticule extraction for hyperopia might be safe, effective, and stable, but its predictability should be improved in the future.

Optical Quality and Intraocular Scattering After Femtosecond Laser Small Incision Lenticule Extraction

PURPOSE To investigate objective optical quality and changes in light scatter after femtosecond laser small incision lenticule extraction (SMILE) for moderate to high myopia correction. METHODS Prospective clinical study of 66 eyes of 66 patients (23 males, 43 females) with a mean age of 28.67 ± 6.62 years, mean spherical refraction of -6.06 ± 1.57 diopters, and mean cylindrical refraction of -0.68 ± 0.46 diopters. Every patient had a 3-month follow-up after a standard SMILE procedure. An optical quality analysis system was used to measure modulation transfer function cutoff frequency (MTFcutoff), Strehl2D ratio, and objective scatter index (OSI). RESULTS At 3 months postoperatively, mean spherical equivalent was 0.03 ± 0.24 diopters and corrected distance visual acuities of all patients were equal to or better than preoperative values, with a mean safety index of 1.12 ± 0.17 (range: 0.80 to 1.50) and mean efficacy index of 1.18 ± 0.21 (range: 0.80 to 1.50). Mean OSI increased from 0.75 preoperatively to 1.09 at 20 days postoperatively (P < .05), and gradually declined to 0.94 at 40 days and 0.82 at 3 months postoperatively (P > .05). MTFcutoff and Strehl2D ratio did not change significantly compared with preoperative values (P > .05). Multiple linear regression analysis revealed that preoperative OSI was significantly correlated with optical quality at 3 months. Patients with less preoperative OSI tended to acquire higher MTFcutoff (b = -8.61) and lower OSI (b = 0.65) (P < .05). CONCLUSIONS SMILE had little impact on retinal image quality after myopia correction. Postoperative OSI showed a temporary increase and then returned to normal.

Femtosecond Laser-Assisted Corneal Small Incision Allogenic Intrastromal Lenticule Implantation in Monkeys: A Pilot Study.

PURPOSE Lenticule implantation can be used to correct vision problems. However, it is significantly restrained by the sources of autologous lenticules. The aim of the present study was to investigate the feasibility and effects of femtosecond laser-assisted corneal small incision allogenic intrastromal lenticule implantation (AILI) in monkeys. METHODS Six healthy adult monkeys were included in this study. Femtosecond lenticule extraction (-4.0 diopter [D] correction, 5.0-mm optical zone) was performed in one eye of two monkeys and both eyes of one monkey. Each extracted refractive lenticule was allogenically transplanted into a femtosecond laser-created corneal stromal pocket in one eye of the other two monkeys and one monkeys both eyes. Pre- and postoperative (1 or 3 days, 1 month, and 6 months) slit lamp microscopy, corneal topography, anterior segment optical coherence tomography, and in vivo confocal microscopy were performed. RESULTS Corneal edema occurred in the early postoperative days with a large number of hyperreflective particles around the borders. Corneal tissue edema gradually decreased. Nerve fiber regeneration could be detected in the lenticule layer at 6 months. Overall, 3.27 ± 1.2 D corneal power was increased at 6 months, accounting for 82% of the intended correction. At the same time point, corneal stroma was 69 ± 11 μm thicker than preoperative ones and was roughly equal to the maximum thickness of implanted lenticules. No significant complications were observed. CONCLUSIONS The AILI technique seems to be feasible and safe for increasing corneal stromal thickness and changing corneal refractive power, which may provide a useful method for treatment of keratoectasia, presbyopia, and hyperopia.