Objective: To compare the surgical induced astigmatism(SIA) of the total, anterior and posterior cornea between eyes with 2.2-mm and 3.0-mm clear corneal incisions in phacoemulsification. Methods: A prospective double-blind randomized controlled study was conducted on 131 patients (131 eyes) with age-related cataract from October 2017 to June 2018. They were randomized according to the random number table. Sixty-nine patients received phacoemulsification through a 2.2-mm clear corneal incision at 140 degrees; 62 patients were recruited in the control group with a 3.0-mm clear corneal incision at the same position. Lens density was graded and compared between the groups preoperatively. Total corneal refractive power (TCRP), simulated keratometry (SimK) and posterior corneal astigmatism (PCA) (Apex, 4-mm zone) were recorded through the Pentacam preoperatively and at 1 week, 1 month and 3 months postoperatively. Corneal astigmatism was decomposed to vertical/horizontal (X) and oblique changes (Y) using the power vector analysis. Independent sample t test and matched t test were used for statistical analysis. Results: A total of 123 patients (123 eyes) completed 3 months of follow-up including 65 in the 2.2-mm group and 58 in the control group. The age of the two groups was (69±9) and (71±10) years old, and the lens density was (2.08±0.47) and (2.12±0.46) grades, respectively. Both the age and the lens density of the two groups were not statistically significant (both P>0.05). Preoperative TCRP, SimK and PCA were not statistically significant (all P>0.05). SIA was calculated using the vector analysis. Centroid SIA conducted from TCRP, SimK and PCA in the 2.2-mm group was -0.11 D@146°, -0.11 D@151° and -0.03 D@67°, respectively, at 3 months postoperatively. In the 3.0-mm group, it was -0.25 D@158°, -0.24 D@147° and -0.04 D@47°, respectively. Statistical significance was found between the two groups in the Y polar value of SIA of the anterior surface [(-0.10±0.30) vs.(-0.22±0.37) D, t=-2.133, P=0.035] and the SIA of the posterior surface [(0.24±0.16) vs. (0.19±0.12) D, t=2.009, P=0.047] at 3 months postoperatively. In the comparison of the SIA of TCRP and anterior surface, statistical significance was found in the absolute value of SIA at all the intervals in the 2.2-mm group [(0.87±0.80) vs. (0.58±0.48) D, (0.58±0.48) vs. (0.50±0.28)D, (0.57±0.37) vs. (0.47±0.28) D, t=5.102, 4.155, 3.877, all P<0.01] and at 1 week and 1 month in the 3.0-mm group [(0.82±0.57) vs. (0.58±0.41) D, (0.59±0.36) vs. (0.50±0.28) D, t=5.034, 3.919, both P<0.01]. X components of SIA(TCRP) and SIA(simk) were significantly different at 3 month postoperatively in 3.0-mm group (P<0.05). Y components of SIA(TCRP) and SIA(SimK) were significantly different at 1 week postoperatively in the 2.2-mm group[(-0.48±0.85) vs.(-0.24±0.42) D, P<0.01] and 3.0-mm group [(-0.58±0.66) vs. (-0.37±0.42) D, P<0.01]. Conclusions: Compared with the 3.0-mm incision, the 2.2-mm coaxial micro-incision cataract surgery has a lower and more stable SIA. The effect of a clear corneal incision in cataract surgery on the total cornea is more obvious than that on the anterior surface of the cornea. The difference is significant in the early stage and gradually decrease with time. (Chin J Ophthalmol, 2019, 55: 495-501).
目的： 比较2.2 mm和3.0 mm透明角膜切口超声乳化白内障吸除术后全角膜、角膜前后表面术源性散光（SIA）的差异。 方法： 前瞻性双盲随机对照研究。收集2017年10月至2018年6月于天津医科大学眼科医院就诊且符合入选标准的年龄相关性白内障患者131例（131只眼），年龄44~93岁。采用随机数字表法将患者随机分成两组，2.2 mm组：同轴2.2 mm微切口超声乳化白内障吸除联合人工晶状体植入术69例（69只眼）；3.0 mm组：同轴3.0 mm小切口超声乳化白内障吸除联合人工晶状体植入术62例（62只眼）。术前及术后1周、1个月和3个月对患者进行随访。术前检查患者白内障核硬度，并采用Emery分级。所有随访时间内，对患者进行Pentacam眼前节生物测量仪检查。记录每一次随访期，以角膜顶点为中心4 mm区域内全角膜屈光力（TCRP）、角膜前表面的模拟角膜屈光力（SimK）和角膜后表面散光（PCA），使用矢量分析方法将散光分解为X-Y径线，计算SIA，并采用Sigma Plot软件进行绘图。采用独立样本t检验、配对t检验等进行统计学分析。 结果： 共123例（123只眼）完成3个月随访，其中2.2 mm组65只眼，3.0 mm组58只眼；两组年龄分别为（69±9）、（71±10）岁；两组晶状体核硬度分级分别为（2.08±0.47）、（2.12±0.46）级，差异均无统计学意义（均P>0.05）。两组术前全角膜、角膜前后表面的屈光力及散光度数差异均无统计学意义（均P>0.05）。术后对所有SIA进行计算及矢量分解，得到的矢量中心（SIA矢量均值）即为质心SIA。术后3个月2.2 mm组TCRP、SimK及PCA的质心SIA分别为-0.11 D@146°、-0.11 D@151°、-0.03 D@67°；3.0 mm组分别为-0.25 D@158°、-0.24 D@147°、-0.04 D@47°。2.2 mm组与3.0 mm组角膜SIA比较，术后3个月2.2 mm组与3.0 mm组SimK的Y经线SIA度数分别为（-0.10±0.30）、（-0.22±0.37）D，PCA的SIA度数绝对值分别为（0.24±0.16）、（0.19±0.12）D，两组间差异均有统计学意义（t=-2.133、P=0.035；t=2.009、P=0.047），其余各径线的分解矢量及SIA绝对值两组间差异均无统计学意义（均P>0.05）。全角膜SIA与角膜前表面SIA比较，2.2 mm组术后1周、1个月和3个月全角膜SIA绝对值分别为（0.87±0.80）、（0.58±0.48）、（0.57±0.37）D，均高于角膜前表面SIA绝对值（0.58±0.48）、（0.50±0.28）、（0.47±0.28）D，差异均有统计学意义（t=5.102、4.155、3.877，均P<0.01）。3.0 mm组术后1周及1个月全角膜SIA绝对值分别为（0.82±0.57）、（0.59±0.36）D，均高于角膜前表面SIA绝对值（0.58±0.41）、（0.50±0.28）D，差异有统计学意义（t=5.034、3.919，均P<0.01）；术后3个月全角膜SIA绝对值与角膜前表面SIA绝对值差异无统计学意义（P=0.186）。2.2 mm组术后1周Y径线全角膜SIA度数为（-0.48±0.85）D，高于角膜前表面SIA度数（-0.24±0.42）D；3.0 mm组术后1周Y径线及术后3个月X径线全角膜SIA度数分别为（-0.58±0.66）、（0.18±0.45）D，均高于角膜前表面SIA度数（-0.37±0.42）、（0.10±0.47）D，差异均有统计学意义（均P<0.05）；两组其余随访时间Y径线及X径线全角膜SIA度数与角膜前表面SIA度数差异均无统计学意义（均P>0.05）。 结论： 相比3.0 mm透明角膜切口手术，2.2 mm同轴微切口白内障摘除手术具有更低且更为稳定的SIA。白内障摘除手术切口对全角膜SIA的影响比角膜前表面SIA更明显，两者差异在术后早期尤为明显，随着手术时间的推移而逐渐减小。（中华眼科杂志，2019，55：495-501）.
Keywords: Astigmatism; Phacoemulsification; Postoperative complications; Refraction, ocular.