| PartⅠThe study of changes in corneal hysteresis (CH) and corneal resistance factor (CRF) following small incision lenticule extraction (SMILE)[Abstract] Purpose To investigate the changes in corneal hysteresis (CH) and corneal resistance factor (CRF) following small incision lenticule extraction (SMILE). Methods In this prospective cohort study,59 eyes of 59 patinets (32 males and 27 females), who were scheduled for corneal refractive surgery, were enrolled, including 39 eyes of 39 patients (26.05±7.38 years,-6.27±1.73D,19 males and 20 females)of SMILE procedure(SMILE group) and 20 eyes of 20 patients (23.70±6.41 years,-3.89±1.64D,13 males and 7 females) of LASER procedure (LASEK group). CH and CRF were measured with the ocular response analyzer (ORA) preoperatively,1 month and 3 months postoperatively. SAS 9.2 software (SAS Institute Inc., Cary, NC) was used. A mixed effect model for repeated measure was used to evaluate the differences in CH and CRF among the three time points. The differences in age, gender and ablation depth between the two groups were statistically adjusted. The correlations between CH, CRF, centre corneal thickness (CCT), ablation depth and the changes of CH and CRF were analyzed with Pearson correlation coefficients. The cut-off P values were 0.05.Results In SMILE group, a significant difference was detected among the three time points (pre-operation,1 month and 3 months after surgery) in the mean values of IOPcc, IOPg, CH, and CRF (P<0.01). Bonferroni-adjusted post hoc comparisons indicated that there was a significant decrease in these values of 1 month and 3 months following SMILE procedure when compared to those obtained pre-operatively (post hoc P<0.01). There was no significant difference in these values between the time points of 1 month and 3 month after surgery (post hoc P>0.05). In LASEK group IOPcc did not change significantly before and after surgery (P>0.05), however, IOPg, CH and CRF decreased significantly 1 month and 3 months after surgery when compared to the values obtained pre-operatively (post hoc P<0.01). There was no significant difference in the mean values of IOPg, CH and CRF between the time points of 1 month and 3 month after surgery (post hoc P>0.05). No significant difference was detected between SMILE and LASEK group in IOPcc, IOPg, CH and CRF at each time point (P>0.05). Three months after SMILE procedure, the values of residue CCT significantly correlated with that of CH(r=0.672, P<0.001) and CRF(r=0.595, P=0.002]. Ablation depth did not significantly correlate with the changes of CH and CRF(P>0.05]. Conclusions Corneal biomechanical properties compromised significantly both following SMILE procedures. Further studies are necessary to confirm the changes in CH and CRF following SMILE.Part IIThe study on corneal deformation parameters after small incision lenticule extraction (SMILE)[Abstract] Purpose To investigate the corneal deformation parameters after femtosecond laser small incision lenticule extraction (SMILE). Methods In this retrospective study,52 eyes of 52 patents (19 males and 33 females), which were 3 months after SMILE, LASEK or FS-LASIK, were enrolled, including 17 eyes (patients) after SMILE,18 eyes (patients) after LASEK and 17 eyes (patients) after FS-LASIK. Corneal deformation parameters were measured with the Corvis ST tonometer (CST) 3 months after these procedures. Statistical analysis was performed using SPSS 19 software (SPSS Inc., IBM, USA) and SAS 9.2 software (SAS Institute Inc., Cary, NC). One-way analysis of variance (ANOVA) with bonferroni-adjusted post hoc comparisons were used to evaluate the differences in corneal deformation parameters, and a p-value of<0.05 was considered significant. Multivariable linear regression model analysis was then applied to adjust for selected covariates (age, pre-operative CCT and pre-operative MRSE) to control for potentially confounding factors, and the alpha level was set at 0.1 to compensate for the small sample sizes and to facilitate detection of statistical trends. Pearson correlation coefficients were carried out to analyze linear relationships between the deformation parameters, and the cut-off P values were 0.05. Results The mean value of deformation amplitude (DA) of the FS-LASIK group was significantly higher than that of the LASEK group (P=0.022). The mean value of applanation time 1, (AT1) of the LASEK group was significantly higher than that of the FS-LASIK group (P=0.038). No significant difference was detected in the mean values of DA and AT1 (p>0.05) between the LASEK group and the SMILE group as well as between the SMILE group and the FS-LASIK group. Multiple lineal regression model analysis revealed that after adjustment for age, pre-operative CCT and pre-operative MRSE, the significance of the difference in the mean values of AT1 and DA between LASEK group and FS-LASIK group were P=0.084 and P=0.059, respectively. In all the three groups, the values of AT1 negatively correlated with those of applanation time (AT2)(SMILE:r=-0.577, P=0.015; LASEK:r=-0.833, p<0.001; FS-LASIK:r=-0.516, P=0.034) and DA (SMILE:r=-0.556, P=0.021; LASEK:r=-0.877, p<0.001; FS-LASIK:r=-0.509, P=0.037). Conclusions Values of AT1 and DA after SMILE may be intermediate between those after LASEK and FS-LASIK.Part ⅢThe study of effect of corneal lenticule extraction on corneal deformation parameters during small incision lenticule extraction (SMILE)[Abstract] Purpose To investigate the effect of corneal lenticule extraction on corneal deformation parameters during small incision lenticule extraction (SMILE) procedure. Methods In this prospective study,18 eyes of 10 patients (27.90±7.11years,-5.64±2.45 diopters,4 males and 6 females) scheduled for SMILE procedure were enrolled. Changes in the corneal deformation parameters, including deformation amplitude (DA), applanation time (AT1 and AT2), applanation length (AL1 and AL2), corneal velocity (CV1 and CV2), peak distance (P.Dist.),radius and the intraocular pressure values were measured preoperatively, immediately after lenticule creation and subsequent to corneal lenticule extraction in all eyes with the Corvis Scheimpflug Technology (Corvis ST, Oculus, Wetzlar, Germany). Statistical analysis was performed using SPSS 19 software (SPSS Inc., IBM, USA). Repeated measures analysis of variance (ANOVA) with bonferroni-adjusted post hoc comparisons was performed to investigate changes following each step of the procedure. The cut-off P values were 0.05. Results The scheimpflug camera of the Corvis ST demonstrated the intralamellar small gas bubbles formed from the vaporisation of tissue after lenticule creation and a gray zone was observed between the cap and the residual stromal bed after lenticule extraction. A significant difference was detected among the three time points (pre-operation, post-lenticule creation and post lenticule extraction) in AT1 (P<0.001), AT2 (P=0.001), DA (P<0.001), and IOP (P=0.002). Bonferroni-adjusted post hoc comparisons indicated that there was no significant change in AT1, AT2, DA, or IOP after lenticule creation (post hoc P>0.05), but there was a significant decrease in these parameters following subsequent corneal lenticule extraction (post hoc P<0.01), when compared to values obtained pre-operatively. Conclusions The changes in corneal deformation parameters following SMILE procedure were mainly caused by stromal lenticule extraction, while lenticule creation with femtosecond laser may not have an obvious effect on corneal deformation properties. |
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