| Objective: To evaluate the accuracy of each intraocular pressure(IOP) measurement values after small incision lenticule extraction(SMILE), analyze the corneal biomechanics influencing factors of IOP measurement before and after SMILE. Furthermore, to investigate the IOP changes after small-incision lenticule extraction(SMILE) and femtosecond laser-assisted laser in situ keratomileusis(FS-LASIK). Regress the equation of IOP variation to estimate the actual IOP.Methods: 1. In this retrospective clinical control study, 116 eyes of 60 patients with myopia and myopic astigmatism undergoing SMILE surgery were included randomly in this study and Ocular Response Analyzer(ORA), Noncontact Tonometer(NCT) and Pentacam system were used to measure IOP values at preoperative and 3 months postoperatively, aquiring 8 kinds of IOPs: IOPg, IOPcc, IOPNCT, Ehlers, Shah, Dresden, Orssengo, Kohlhaas. The comparison of 8 IOPs between pre- and post- operation were analyzed with paired t-testing; the Pearson correlation coefficient(r) and spearman correlation coefficient(rs) were used to evaluate the relationship between pre-, post-operative IOPs and the influencing factors.2. In this retrospective clinical control study, a total of 393 eyes of 204 patients who underwent SMILE(197 eyes, 103 patients) and FS-LASIK(196 eyes, 101 patients) were included. Data were collected preoperatively and at 1, 3 and 6 months postoperatively, which included values of Goldmann-correlated IOP(IOPg), corneal-compensated IOP(IOPcc), corneal hysteresis(CH) and corneal resistance factor(CRF) by Ocular Response Analyzer(ORA), and values of intraocular pressure(IOPNCT) by Noncontact Tonometer(NCT), and intraocular pressure values of Ehlers, Shah, Dresden, Kohlhaas, Orssengo/Pye by Pentacam corrected system. All IOP values at different examination points within a group were compared by repeated-measures analysis of variance and the further pairwise comparison used least-significant difference(LSD). The statistical significance of differences between the two groups at different follow-up time also adopted LSD. The comparison of IOP changes between two groups were performed using independent t-test. The Pearson correlation coefficient(r) was used to evaluate the correlations between variables. The regression analysis of intraocular pressure variation ΔIOPNCT and influencing factors was analyzed with multiple linear regression analysis.Results:1. The preoperative IOPg, IOPcc, IOPNCT, Ehlers、Shah、Dresden、Orssengo and Kohlhaas were all correlated with the CRF(r=0.647, 0.248, 0.710, 0.290, 0.425, 0.497, 0.489, 0.664;P<0.01), the preoperative IOPg,IOPNCT, Ehlers, Shah were correlated with CCT(r=0.260,0.259,-0.418,-0.245,P<0.01).2. Moderate positive correlation was significantly shown between the postoperative IOPs and the preoperative IOPs(r≥0.5,P<0.01), the postoperative IOPg, Ehlers, Shah, Dresden were correlated with the postoperative CCT(P<0.05),the postoperative IOPg, IOPNCT, Orssengo/Pye, Kohlhaas were correlated with the postoperative CRF(r=0.707,0.549,0.276,0.346,P<0.01), the postoperative IOPg, IOPcc, IOPNCT, Ehlers, Shah and were correlated with postoperative CH(r=0.296,-0.366,0.270,-0.349,-0.197,P<0.05).3. The comparison of IOPs before and after SMILE, Pentacam Shah program showed no difference between pre-, post-operative IOP values(t=-0.08,P=0.940), the comparison of other IOPs before and after SMILE have statistical significance(P<0.001).4. All the IOP measurement values including IOPg, IOPcc, IOPNCT, Shah, Dresden, Orssengo/Pye and Kohlhaas decreased significantly at 3, 6 months after SMILE and FS-LASIK(P<0.01). Among these IOP measurement values the Ehlers and Shah values were found to be more closed to preoperative IOP values for both SMILE and FS-LASIK groups, with the IOP measurement errors of about 1mm Hg at 6 months. The decrease in postoperative IOP was significant when measured using IOPg about 6 mm Hg, IOPcc about 3 mm Hg, IOPNCT about 5 mm Hg and other Pentacam correction formula about 2 mm Hg.5. In SMILE, all the IOP measurement values showed no significant difference between 3 and 6 months(P>0.05). Whereas, in FS-LASIK IOPNCT、Ehlers、Shah、Dresden, Kohlhaas and Orssengo/Pye had significant difference between 3 and 6 months(P<0.05).6. Moreover, at 6 months after surgery, the change of IOPg(ΔIOPg) in FS-LASIK was higher than SMILE(6.75±2.61 vs.5.85± 2.40, P=0.03), the other IOP changes showed no significance(P>0.05).7. After SMILE and FS-LASIK, the corneal biomechanics CH, CRF, the corneal keratometry, the flat K, steep K and mean K also decreased significantly at 1, 3 and 6 months over preoperative values(P<0.01).8. At 6-month follow-up time, the corneal biomechanical parameters ΔCRF, ΔCH and ΔKs in FS-LASIK were higher than SMILE(4.10±1.47 vs. 3.52±1.16;2.45±1.21 vs. 2.08±1.11; 4.87±1.88 vs. 4.29±1.08; P=0.005, 0.045, 0.016, respectively).9. Correlation analysis showed the ΔIOPg, ΔIOPcc, ΔIOPNCT in FS-LASIK group had more influencing factors than SMILE. The ΔIOP after FS-LASIK had correlation with the preoperative IOP and two corneal biomechanics parameters ΔCRF, ΔCH(P<0.05). While after SMILE, ΔIOPg, ΔIOPNCT were related with the preoperative IOP and corneal biomechanics ΔCRF(r=0.585, 0.235; P<0.05), ΔIOPcc was related with the preoperative IOP and corneal biomechanics ΔCH(r=-0.543, P<0.05).10. The multiple linear regression models were constructed to explore factors influencing IOP variations in both groups at 3-month follow-up time. The preoperative IOP and postoperative CRF, CH and flat keratometry were enrolled into the regression equations in both groups. After SMILE, IOPNCT=IOPmeasured+0.738IOPpre-- 1.635CRFpost- + 1.375 CH post- + 0.301ΔKf-8.118, while after FS-LASIK the IOPNCT=IOPmeasured+0.705 IOP pre--1.650 CRF post-+1.288 CH post--0.368 Kf post-+8.573.Conclusions:1. IOP values were affected by the central corneal thickness and corneal biomechanics. The postoperative IOP after SMILE and FS-LASIK had correlation with the preoperative IOP, corneal thickness and the corneal biomechanics. Furthermore, ΔIOP in FS-LASIK group had more influencing factors than SMILE.2. In both SMILE and FS-LASIK, compared with the preoperative IOP, all the IOP measurement values decreased significantly after surgery, and they showed the same IOP change trends. The IOP measurement values showed stable at 3-month after SMILE, while, FS-LASIK requires a long time observation. So the SMILE surgery had less influence on IOP measurement values.3. Among these IOP measurement values, the Ehlers and Shah values from Pentacam were found to be more closed to preoperative IOP values for both SMILE and FS-LASIK groups, with the minimum IOP measurement errors of about 1mm Hg at 6 months providing relatively reliable postoperative IOP. The next were other Pentacam correction formula(about 2 mm Hg), IOPcc(about 3 mm Hg), IOPNCT(about 5 mm Hg) and IOPg(about 6 mm Hg).4. The best-fit models we constructed, which after SMILE surgery IOPNCT=IOPmeasured+0.738 IOP pre--1.635CRFpost-+1.375 CH post-+0.301ΔKf-8.118, while after FS-LASIK surgery the IOPNCT = IOPmeasured + 0.705 IOP pre--1.650 CRF post- + 1.288 CH post-- 0.368 Kf post- + 8.573, may be useful for clinician to evaluate the postoperative IOP. |
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