飞秒激光小切口角膜基质透镜取出术术后角膜生物力学的影响因素分析

背景 角膜屈光手术术后的视觉效果和角膜生物力学改变是值得关注的问题,飞秒激光小切口角膜基质透镜取出术(SMILE)在临床上显示了较好的术后视觉效果,但其对角膜生物力学的长期影响及其影响因素尚不十分清楚. 目的 探讨SMILE术后角膜生物力学的改变及其主要的影响因素.方法 采用系列病例观察研究方法,纳入2011年8月至2013年7月在天津市眼科医院拟行SMILE的患者58例100眼,患眼术前平均球镜度为(-5.00±1.55)D,平均柱镜度为(-0.98±0.87)D.分别于术前及术后1、3、6、12个月时采用眼反应分析仪(ORA)进行角膜生物力学参数测量,包括角膜阻力因子(CRF)和角膜滞后量(CH).术眼按切削比(LTR)、术前CRF值和术后残余基质床厚度(RST)的不同分为低、中、高组,分析3种不同因素与术后ΔCRF和ΔCH的关系,并分析术前相关参数,如年龄、等效球镜度、球镜度与柱镜度之和、透镜厚度、RST/术前中央角膜厚度(CCT)、术前CCT、术前Km与术后ΔCRF和ΔCH的关系.结果 SMILE术后1个月CRF和CH值分别为(7.12±1.20)mmHg(1 mmHg=0.133 kPa)和(7.90±0.97) mmHg,均明显低于术前的(10.17±1.46) mmHg和(10.00±1.16) mmHg,差异均有统计学意义(t=15.552,P=0.000;t=13.411,P=0.000).术后3、6和12个月术眼CRF值分别为(7.06±0.90)、(6.98±1.11)和(6.87±1.07)mmHg,CH值分别为(8.12±0.84)、(8.12±0.97)和(8.14±0.86) mmHg,与各自前一时间点CRF值和CH值比较差异均无统计学意义(CRF:P=0.848、0.992、0.270;CH:P=0.370、0.791、0.777).ΔCRF和ΔCH与LTR、术前CRF值及术前CH值均呈正相关(LTR:r=0.468,P=0.000;r=0.299,P=0.004;CRF:r=0.696,P=0.000;r=0.590,P=0.000;CH:r=0.576,P=0.000;r=0.690,P=0.000).术后12个月术眼ΔCRF和ΔCH值与术前等效球镜度、术前球镜与柱镜度之和及术后RST/术前CCT均呈负相关(等效球镜度:r=-0.496,P=0.000;r=-0.292,P=0.010;球镜与柱镜度数之和:r=-0.484,P=0.000;r=-0.293,P=0.005;RST/术前CCT:r=-0.362,P=0.000;r=-0.243,P=0.019),而与透镜厚度均呈正相关(r=0.495,P=0.000;r=0.325,P=0.002).此外,ΔCRF和ΔCH值与患者年龄、术前CCT和术前Km均无明显相关(均P＞0.05). 结论 术眼SMILE术后早期角膜生物力学强度减弱,术后1个月角膜生物力学逐渐恢复并达到稳定状态.RST/术前CCT越大,SMILE对角膜生物力学强度的保护作用越大.除术前CRF和CH外,影响SMILE术后角膜生物力学的主要因素还有透镜厚度和预矫正度数.

Influencing factors of corneal biomechanics following small incision lenticule extraction

Background The visual quality and corneal biomechanical change are two major sides for evaluating the outcomes of cornea refractive surgery.It was determined that small incision lenticule extraction (SMILE) can improve the visual outcomes,but its long-term effects on corneal biomechanical are not known clearly.Objective This study was to investigate the change of corneal biomechanics and influence factors following SMILE.Methods A serial cases-observional study was performed.One hundred eyes of 58 patients with a mean spherical diopter (-5.00 ± 1.55) D and cylindrical diopter (-0.98 ± 0.87) D were included in Tianjin Eye Hospital from August 2011 to July 2013 under the informed consent.Corneal biomechanical parameters,including corneal resistance factor (CRF) and cornea hysteresis (CH) were measured using the ocular response analyzer (ORA) in preoperation and postoperative 1,3,6 and 12 months,respectively.The patients were grouped based on different lenticule thickness ratio (LTR),preoperative CRF values and residual stromal thickness (RST) separately,and the correlations of LTR,preoperative CRF and RST with ΔCRF and ΔCH were assessed.In addition,the associations between ΔCRF or ΔCH and related preoperation parameters were evaluated.Results The CRF and CH values at postoperative 1 month were (7.12 ± 1.20) mmHg and (7.90 ± 0.97) mmHg,which were significantly lower than preoperative (10.17±1.46) mmHg and (10.00±1.16) mmHg,respectively (t=15.552,P=0.000;t =13.411,P=0.000).The CRF values at postoperative 3,6 and 12 months were (7.06±0.90),(6.98 ± 1.11) and (6.87 ± 1.07) mmHg,and those of CH were (8.12 ±0.84),(8.12 ±0.97) and (8.14 ±0.86) mmHg,and no significant differences were found in CRF and CH between the adjacent time points (CRF:P =0.848,0.992,0.270;CH:P =0.370,0.791,0.777).Positive correlations were seen between the ΔCRF or ΔCH and LT/preoperative central corneal thickness (CCT) (LTR),preoperative CRF or preoperative CH values,respectively (LTR:r =0.468,P =0.000;r =0.299,P =0.004;preoperative CRF:r =0.696,P =0.000;r =0.590,P =0.000;preoperative CH:r =0.576,P =0.000;r =0.690,P =0.000).ΔCRF and ΔCH were negatively correlated with preoperative spherical equivalent diopter (r =-0.496,P =0.000;r =-0.292,P =0.010),the sum of preoperative spherical diopter and cylindrical diopter (r =-0.484,P =0.000;r =-0.293,P =0.005) or RST/preoperative CCT (r =-0.362,P =0.000;r =-0.243,P =0.019) and were positively correlated with lenticule (r =0.495,P =0.000;r =0.325,P =0.002).No significant association was found between ΔCRF or ΔCH and age,preoperative CCT and preoperative mean keratometry (all at P＞0.05).Conclusions Corneal biomechanical strength is decreased at the early stage after SMILE.However,biomechanical strength gradually enhances 1 month after surgery and tends to stability.The large RST/preoperative CCT can improve postoperative CRF and CH.The another main factor affecting the corneal biomechanics after SMILE is corrected-diopter.