Objective: To investigate the effect of optical zone diameter on corneal biomechanical properties after small incision lenticule extraction (SMILE). Methods: In this prospective case-control study, 62 eyes of 42 patients with myopia and myopic astigmatism that had undergone SMILE procedure were divided into 2 groups according to the optical zone (OZ) diameter: group A, 31 eyes of 19 patients, OZ= 6.5 mm; group B, 31eyes of 23 patients, OZ=6.0 mm. These patients were examined for corneal hysteresis (CH) and corneal resistance factor (CRF) with the Ocular Response Analyzer (ORA) preoperatively and at 1 week, 1 month and 3 months postoperatively; at the same time, the central corneal thickness-corrected indices of DifCH and DifCRF were calculated. Pearson correlation was applied to analyze the correlation between CH and CRF and central corneal thickness. Independent-samples t test was utilized to compare CH and CRF between the two groups. Repeated ANOVA was used to compare the difference of corneal biomechanical properties at different follow-up timepoints. Results: The preoperative mean CRF and CH values were (10.13±1.19) mmHg and (9.65±1.12) mmHg in group A and (10.34±0.89) mmHg and (10.04± 1.05) mmHg in group B, respectively, and no significant differences were found in CRF and CH between the two groups (CRF: t=-0.807, P=0.423. CH: t=-1.405, P=0.165). The mean CRF values in group A at postoperative 1 week and 3 months were (6.62 ± 1.09) mmHg and (6.83 ± 1.07) mmHg, respectively, which were significantly lower than the relevant mean CRF values in group B (t=-2.703, P=0.009. t=-3.733, P= 0.001). Meanwhile, the mean CH values at 1 week, 1 month and 3 months postoperatively in group A were (7.31±1.06) mmHg, (7.37±0.96) mmHg and (7.82±0.97) mmHg, respectively, which were significantly lower than those in group B (t=-2.415, P=0.019. t=-2.113, P=0.039. t=-2.67, P=0.01). Moreover, the DifCRF and DifCH values in group A were significantly lower than those in group B at 3 months postoperatively (t=-3.409, P=0.001. t=-2.064, P=0.044). The CRF and CH values in both groups showed a significant reduction at 1 week, 1 month and 3 months postoperatively (P<0.05). Conclusions: The size of optical zone has some effects on corneal biomechanical properties after SMILE. The smaller optical zone diameter has a relatively smaller effect. (Chin J Ophthalmol, 2017, 53:182-187).
目的： 探讨飞秒激光小切口角膜基质透镜取出术（SMILE）光学区大小对术后角膜生物力学特性的影响。 方法： 前瞻性病例对照研究。入选天津市眼科医院屈光手术中心拟行SMILE手术的近视眼及近视散光患者62只眼（42例），其中男性22例（32只眼），女性20例（30只眼），年龄（24.1±4.6）岁。根据光学区大小分为两组：A组19例（31只眼），光学区直径为6.5 mm; B组23例（31只眼），光学区直径为6.0 mm。所有研究对象于术前及术后1周、1个月、3个月进行眼反应分析仪（ORA）检查，分别记录角膜滞后量（CH）及角膜阻力因子（CRF），同时计算出角膜中央厚度校正的角膜滞后量（DifCH）和角膜中央厚度校正的角膜阻力因子（DifCRF）。采用Pearson相关分析评估角膜中央厚度与CRF和CH之间的相关关系。所有数据符合正态分布，采用独立样本t检验比较两组研究对象间各测量结果间的差异；采用重复测量方差分析比较两组研究对象术前与术后各随访时间点间各测量结果的差异。 结果： A两组术前CRF和CH值分别为（10.13±1.19）和（9.65±1.12) mmHg (1 mmHg=0.133 kPa），B组术前CRF和CH值分别为（10.34±0.89）和（10.04±1.05）mmHg，两组间差异均无统计学意义（CRF:t=-0.807，P=0.423；CH: t=-1.405 ，P=0.165）；A组术后1周和3个月CRF值分别为（6.62±1.09）和（6.83±1.07 ）mmHg，均小于B组（7.32±0.96）和（7.82±0.90 ）mmHg，差异均有统计学意义（t=-2.703 ，P=0.009和t=-3.733 ，P=0.001）；A组术后1周，1个月和3个月CH值分别为（7.31±1.06）、（7.37±0.96）和（7.82±0.97 ）mmHg，均小于B组（7.87±0.76）、（7.89±0.99）和（8.46±0.81 ）mmHg，差异均有统计学意义（t=-2.415，P=0.019；t=-2.113，P= 0.039；t=-2.67，P=0.01）；A组术后3个月DifCRF和DifCH值分别为（-1.61±0.80）和（-1.05±0.85 ）mmHg，均小于B组DifCRF和DifCH值（-0.85±0.88）和（-0.60±0.79），差异具有统计学意义（t=-3.409，P=0.001和t=-2.064，P=0.044 ）；两组研究对象术后各随访时间点（术后1周、1个月、3个月）CH、CRF值与术前相比均有所下降，差异均有统计学意义（均P<0.05）。 结论： 不同光学区设定对角膜生物力学特性的影响不同，较小光学区对角膜生物力学特性的影响相对较小。（中华眼科杂志，2017，53：182-187）.
Keywords: Biomechanics; Cornea; Corneal curgery, laser; Corneal pachymetry; Corneal stroma; Laser, femtosecond.