Xingtao Zhou

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.

Small incision lenticule extraction (SMILE) and femtosecond laser LASIK: comparison of corneal wound healing and inflammation

Aim To evaluate and compare early corneal wound healing and inflammatory responses after small incision lenticule extraction (SMILE) versus femtosecond laser laser in situ keratomileusis (LASIK). Methods Thirty-six eyes of 36 rabbits underwent SMILE, while another 36 eyes of 36 rabbits were treated with femtosecond laser LASIK. All the eyes were subjected to the same refractive correction of −6.00 DS/−1.00 DC. Twelve eyes that had no surgery were included for control. After euthanisation, corneal tissue sections were evaluated with terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick-end labelling (TUNEL) assay to detect apoptosis at postoperative 4 and 24 h, immunocytochemistry for Ki67 to detect keratocyte proliferation at postoperative day 3, week 1 and month 1, and immunocytochemistry for CD11b to detect inflammation at postoperative day 1, day 3 and week 1, respectively. Results No adverse effects were noted after SMILE or LASIK. Corneal healing postoperatively was uneventful in all cases. There were significantly fewer TUNEL-positive corneal stromal cells after the SMILE procedure at 4 and 24 h postoperatively (p<0.01) compared with the LASIK procedure. In addition, immunocytochemistry showed significantly fewer Ki67-positive cells in the SMILE group than those in the femtosecond laser LASIK group at day 3 and week 1 postoperatively (p<0.05), but there was little expression of Ki67 at month 1 postoperatively in both groups. The CD11b-positive cells were significantly fewer in the SMILE group at day 1, day 3 and week 1 postoperatively (p<0.01). Conclusions SMILE induces less keratocyte apoptosis, proliferation and inflammation compared with femtosecond laser LASIK.

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.

Correlation Between TGF-β1 in Tears and Corneal Haze Following LASEK and Epi-LASIK

PURPOSE To compare the incidence and degree of corneal haze formation following laser subepithelial keratomileusis (LASEK) and epithelial laser in situ keratomileusis (epi-LASIK), and examine its correlation with tear film transforming growth factor-beta1 (TGF-beta1) levels. METHODS This prospective, interventional, clinical trial included 20 eyes (20 patients) randomly assigned to undergo LASEK or epi-LASIK. The level of TGF-beta1 in tear fluid was measured preoperatively and 1, 3, and 5 days postoperatively. Corneal haze was graded at 1 and 3 months after surgery, and the relationship with TGF-beta1 levels was determined. RESULTS Mean preoperative spherical equivalent refraction was -4.50 +/- 1.44 diopters (D) (range: -1.50 to -6.00 D) for LASEK eyes and -4.90 +/- 1.26 D (range: -1.75 to -6.00 D) for epi-LASIK eyes. Although mean corneal haze scores at 1 month were significantly higher in LASEK-treated eyes than in epi-LASIK treated eyes (P=.031), these scores were similar at 3 months (P=.608). Tear fluid TGF-beta1 levels were similar in LASEK and epi-LASIK eyes before surgery (P=.458) and significantly higher in the LASEK group at 1, 3, and 5 days postoperatively (P=.015, P=.023, and P=.039, respectively). A positive correlation was noted between tear TGF-beta1 levels on the first postoperative day and the degree of corneal haze at 1 month (r=0.501, P=.016). CONCLUSIONS Less corneal haze was noted after epi-LASIK than LASEK. A positive correlation between corneal haze and tear fluid TGF-beta1 levels on the first postoperative day suggest a possible mechanism for the observed difference.

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.

Incidence of Myopia in High School Students with and without Red-Green Color Vision Deficiency

PURPOSE To investigate the influence of color vision on myopia development by testing refraction error and axial length of the eye for high school students with and without color vision deficiency (CVD). METHODS A school-based cross-sectional, cluster sample study was conducted to test the color vision and refractive error of 16,539 high school students. Students were screened for CVD using a pseudoisochromatic plate. CVD was confirmed in students failing the test using a Farnsworth-Munsell 100-Hue Test which also served to classify the subtype (protan or deutan). Three classmates of each CVD subject, matched in five myopia risk factors, were chosen to form the normal color vision (CN) control group. Ophthalmic examinations were performed to determine refractive status and axial length. RESULTS Of the students, 309 were found to have red-green CVD and 927 were selected as the CN control group. The prevalence of myopia in the CVD group (45.6%) was significantly lower than that of the CN group (65.8%; P<0.001). The CVD group was also less myopic in refraction (P<0.001) than CN, and protan subjects had shorter axial lengths than those in the control group (P=0.007). CONCLUSIONS Color vision deficiencies appear to influence the development of myopia. The observed lower incidence of myopia in people with CVD may be linked to the reduced functionality of the L/M chromatic mechanism.

One-year outcomes of Epi-LASIK for myopia

PURPOSE To evaluate the early clinical outcomes of epi-LASIK for myopia. METHODS This study comprised 302 eyes of 162 patients. Epi-LASIK was performed with an automatically rotational epikeratome (KM-5000D). Epithelial separation was achieved mechanically without the use of alcohol. After laser ablation, the epithelial sheet was repositioned and a therapeutic contact lens was applied to the cornea immediately for 3 to 5 days. Postoperative visual acuity, symptoms, epithelial sheet, contrast sensitivity, wavefront aberration, and haze formation were evaluated 3, 6, and 12 months postoperatively. RESULTS Of the 302 eyes, 72 eyes (42 patients) with a mean spherical equivalent refraction of -9.13 +/- 4.23 diopters (D) (range: -1.25 to -19.0 D) had > 1-year follow-up. One eye failed to make the epithelial sheet because of the narrow palpebral fissure. An integrated epithelial sheet with a diameter of 8 to 9 mm was made in 289 (95.7%) eyes, leaving a superior hinge of approximately 2 to 4 mm. In 1 eye, stromal tissue remained in the epithelial sheet. Free epithelial flaps were made in 12 (4%) eyes. Mild discomfort was reported by 150 patients (282 eyes, 93.4%). Twelve patients (20 eyes, 6.6%) reported moderate symptoms. At 1 day postoperatively, corneal epithelium was almost transparent or had mild focal edema in 288 (95.4%) eyes; moderate edema was reported in 14 (4.6%) eyes. At 1 year postoperatively, spherical equivalent refraction of 60 (83.3%) eyes was within +/- 1.0 D of attempted refraction. Grade 0.5 haze was found in 2 eyes; all other eyes had no haze. No eye lost any lines of best spectacle-corrected visual acuity (BSCVA), whereas 12 (16.7%) of 72 eyes gained one or two lines of BSCVA. Contrast sensitivity decreased 1 month postoperatively and was restored to preoperative levels in eyes with preoperative spherical equivalent refraction < -10.0 D. Higher order aberration increased significantly postoperatively. CONCLUSIONS Epi-LASIK is a safe and efficient method to correct myopia with the advantage that it has only mild symptoms and mild haze. A larger study with longer follow-up is needed to determine its long-term clinical outcomes.

Evaluation of the repeatability of the Lenstar and comparison with two other non-contact biometric devices in myopes

The aim was to evaluate the repeatability of a new optical low‐coherence reflectometric device Lenstar, as well as its agreement with the IOL Master and the Pentacam‐HR system in myopes.