角膜屈光手术是目前屈光手术的主流术式，随着全飞秒、全激光手术方式的发展，手术变得更加安全精准，不仅角膜创伤小，术后恢复时间也进一步缩短。角膜具有屈光特性和典型的生物软组织力学特性，角膜力学特性不仅参与维持角膜形态，影响角膜手术尤其屈光手术的效果及预后，而且还与部分角膜疾病的发生和发展密切相关。近年来生物力学研究发展迅速，其在眼部疾病的诊疗中发挥着越来越重要的作用。角膜生物力学的变化与术前角膜的形态、不同手术方式的选择、术后角膜厚度的改变等多种因素相关，但手术导致的角膜自身形态改变是不可逆的，若术后角膜生物力学的变化较大，可能会引起医源性角膜扩张、继发性圆锥角膜等并发症的发生。为了规避术后角膜扩张风险和指导个性化的术式选择，了解角膜生物力学特性的影响至关重要。文章对角膜的基础结构、角膜生物力学特性、生物力学测量方法和不同术式及不同角膜瓣厚度术后生物力学变化的研究进展进行综述，为近视患者的个性化精准治疗提供理论指导。

Corneal refractive surgery is currently main stream of refractive surgery. With the development of femtosecond and laser surgery, the surgery has become safer and more accurate, resulting in less corneal trauma and a shorter postoperative recovery time. In recent years, biomechanics research has rapidly progressed, and its clinical application has gradually increased. The cornea not only possesses refractive properties but also exhibits typical biological soft tissue mechanical properties. Corneal mechanical properties not only play a role in maintaining corneal morphology but also influence the outcome and prognosis of corneal surgery, especially refractive surgery, and are closely related to the occurrence and development of some corneal diseases. Corneal refractive surgery involves cutting the cornea according to the patient's diopter, which disrupts the integrity of the cornea and inevitably affects its biomechanical stability. Changes in corneal biomechanics are associated with various factors, such as preoperative corneal morphology, the selection of different surgical methods, and postoperative changes in corneal thickness. However, the self-morphology changes caused by surgery are irreversible. If the postoperative changes in corneal biomechanics are significant, it may lead to complications such as postoperative corneal dilation and secondary keratoconus. To avoid postoperative iatrogenic corneal dilation and guide personalized surgical choice, it is crucial to understand the limits of influence of corneal biomechanical properties. This article reviews the research progress regarding corneal biomechanical properties and changes associated with corneal refractive surgery.

目的：比较角膜生物力学分析仪(Corvis ST)、A型超声测厚仪(A超)、Lenstar LS 900(Lenstar)在测量近视眼角膜厚度的差异，为屈光术前筛查提供参考。方法：纳入2020年3至12月佛山市第二人民医院收治的屈光术前近视患者244例(244只右眼)，并按中央角膜厚度(central corneal thickness，CCT)将患者分为3组：薄角膜组(CCT≤520 μm)、正常角膜组(520 μm570 μm)，分别采用Corvis ST、A超、Lenstar三种仪器测量3组患者的中央角膜厚度，并纳入对比指标。结果：Corvis ST与A超、Lenstar在薄角膜组、正常角膜组、厚角膜组的测量值对比差异均有统计学意义(均P<0.05)；在相关性方面，Corvis ST与A超、Lenstar在薄角膜组、正常角膜组、厚角膜组呈正相关(r=0.841，P<0.001 vs r=0.832，P<0.001；r=0.866，P<0.001 vs r=0.918，P<0.001；r=0.497，P<0.001 vs r=0.801，P<0.001)；在一致性方面，Corvis ST与A超、Lenstar在薄角膜组、正常角膜组、厚角膜组上一致性系数ICC及95%置信区间分别为0.602(0.091，0.857)，0.758(0.221，0.901)、0.741(0.207，0.890)，0.845(0.396，0.938)、0.417(0.005，0.679)，0.667(0.172，0.851)，95%一致性区间范围分别是(-2.2~24.2 μm，-6.7~19.5 μm；-8.4~24.6 μm，-6.8~19.4 μm；-8.7~23.8 μm，-7.0~18.3 μm)。结论：通过对3组数据统计分析得出，Corvis ST与A超、Lenstar的测量值相比，差异均有统计学意义，且Corvis ST的测量值均高于后两种仪器；Corvis ST与后两者均有着较高的相关性，且在正常角膜厚度测量上相关性最高；在一致性方面，从ICC点估计及95%置信区间数值分析，一致性较差；从Bland-Altman角度分析，Corvis ST与后两者的绝对值最大差值超过10 μm，一致性较差，但在与Lenstar的绝对值最大差值均在20 μm内。因此，在测量精度要求较高的屈光手术筛查方面，Corvis ST与A超、Lenstar之间不能相互替代，而对于大规模临床筛查，其角膜厚度测量值对眼压的影响有一定的临床参考意义。

Objective: To compare the differences of corneal thickness measured by corneal biomechanical analyzer (Corvis ST), A-mode ultrasonic thickness meter (A-ultrasound) and Lenstar LS 900 (Lenstar) in myopia, so as to provide reference for preoperative screening of refractive surgery. Methods: A total of 244 patients (244 right eyes) with myopia before refractive surgery in Foshan Second People’s Hospital from March to December 2020 were included in the study, and the patients were divided into three groups according to the central corneal thickness (CCT): the thin cornea group (CCT≤520 μm), the normal cornea group (520 μm570 μm). The central corneal thickness (CCT) of the three groups was measured by Corvis ST, A-type ultrasonic thickness gauge and Lenstar LS 900, respectively, and included in the comparison index. Results: The measured values of Corvis ST, A-ultrasound and Lenstar in the thin cornea group, the normal cornea group and the thick cornea group were statistically significant (all P<0.05). Corvis ST was positively correlated with A-ultrasound and Lenstar in the thin cornea group, the normal cornea group and the thick cornea group (r=0.841, P<0.001 vs r=0.832, P<0.001; r=0.866, P<0.001 vs r=0.918, P<0.001; r=0.497, P<0.001 vs r=0.801, P<0.001). In terms of consistency, the consistency coefficients ICC of Corvis ST, A-ultrasound and Lenstar in the thin cornea group, the normal cornea group and the thick cornea group were 0.602 (0.091, 0.857), 0.758 (0.221, 0.901); 0.741 (0.207, 0.890), 0.845 (0.396, 0.938); 0.417 (0.005, 0.679), 0.667 (0.172, 0.851), and the range of 95% consistency interval were -2.2–24.2 μm, -6.7–19.5 μm; -8.4–24.6 μm, -6.8–19.4 μm; -8.7–23.8 μm, -7.0–18.3 μm. Conclusion: Through the statistical analysis of the data from the three groups, it is concluded that the measured values of Corvis ST are statistically significant compared with those of A-ultrasound and Lenstar, and the measured values of Corvis ST are higher than those of the latter two instruments. Corvis ST has a high correlation with the latter two, and the correlation is the highest in the measurement of normal corneal thickness. In terms of consistency, from the ICC point estimation and 95% confidence interval numerical analysis, the consistency was poor. From the perspective of Bland Altman, the maximum absolute value difference between Corvis ST and Lenstar was more than 10 μm, indicating poor consistency, but the maximum absolute value difference between Corvis ST and Lenstar was within 20 μm. Therefore, in refractive surgery screening with high measurement accuracy, Corvis ST, A-ultrasound and Lenstar cannot replace each other. However, in large-scale clinical screening, the measured value of corneal thickness has a certain clinical reference significance on the impact of intraocular pressure.

目的：基于新一代Corvis^® ST分析成人近视患者经飞秒激光小切口角膜透镜取出术(small incision corneal lens extraction，SMILE)后角膜体(corneal volumn，CV)的变化与角膜生物力学变化的相关性，进一步证明C V对于评估SMILE术后角膜生物力学特性以及预测屈光手术结果的价值。方法：采用前瞻性病例观察研究方法，纳入2021年1月至8月在佛山市第二人民医院拟行SMILE的成人近视患者72例(72眼)。为避免双眼相关性，纳入患者的一个合适眼(右眼或者左眼)，根据术前中央角膜厚度，将厚度470~<530 μm分为低角膜厚度组，530~<560 μm为中角膜厚度组 ， ≥560μm为高角膜厚度组。应用新一代 Corvis^® ST 于术前和术后3个月测量非接触生物力学校正眼压(biomechanical intraocular pressure，bIOP)、2 mm处变形幅度的比值[DA ratiomax(2 mm)，DA2ratio]、综合半径(integrated inverse concave radius，IR)、水平方向Ambr?sio相关厚度，最薄点厚度/厚度变化率(Ambrósio’s relational thickness，ARTh)、第1次压平时角膜硬度参数(stiffness parameter applanation 1，SP-A1)、Corvis生物力学指数(Corvis biomechanical index，CBI)和应力和应变参数(stress-strain index，SSI)7项角膜生物力学参数。应用Pentacam眼前节分析系统测量中央角膜厚度(central corneal thickness，CCT)和不同区域的CV(CV_3mm、CV_5mm、CV_7mm和CV_10mm)。对比SMILE术前与术后3个月的CV、角膜生物力学参数的变化，并分析角膜生物力学参数与CV的相关性。数据采用配对、独立样本t检验分析差异性；单因素方差分析不同角膜厚度组的差异性；Spearman相关性分析和偏最小二乘回归(partial least squares linear regression，PLSLR)分析相关性。结果：SMILE术后3个月，CV_3mm、CV_5mm、CV_7mm和CV_10mm均较术前显著下降(均P<0.001)；bIOP、ARTh、SP-A1和SSI较术前明显下降(P<0.05)；DA2ratio、IR和CBI较术前明显升高(P<0.05)。术前和术后3个月不同角膜厚度组的ARTh、SP-A1DA2ratio、IR和CBI差异均有统计学意义(均P<0.05)，低中角膜厚度组SSI术前后变化不大(P>0.05)。术前DA2ratio与CV_3mm、CV_5mm呈负相关，与CV_10mm呈正相关；ARTh与CV_3mm、CV_5mm呈正相关，与CV_10mm呈负相关；bIOP与CV_10mm呈正相关；IR与CV_3mm、CV_5mm呈负相关，与CV_10mm呈正相关；SP-A1与CV_3mm、CV_5mm呈正相关，与CV_10mm呈负相关；CBI与CV_3mm、CV_5mm和CV_10mm呈负相关，SSI与CV_3mm呈正相关，与CV_10mm呈负相关。SMILE术后3个月，ARTh与CV_3mm、CV_5mm呈正相关，与CV_10mm呈负相关；CBI与CV_3mm负相关、CV_10mm呈正相关(均P<0.05)。SMILE术后3个月变化量中，ARTh与CV_3mm、CV_5mm呈正相关，与CV_10mm负相关；CBI与CV_3mm呈负相关，与CV_10mm呈正相关(均P<0.05)。结论：成人SMILE术后3个月CV_3mm、CV_5mm、CV_7mm、CV_10mm、眼压和CCT较术前均显著降低；越往周边区域CV减少量越多。SMILE术后3个月的新一代Corvis^® ST角膜生物力学新型参数较术前有显著变化；不同区域CV与角膜生物力学参数存在一定的相关性，预期SMILE术后不同区域的CV可以表征术后部分角膜生物力学特性的改变，CV可能成为表征预测角膜扩张发展的参数因素。

Objective: To evaluate the changes in corneal volume (CV) and the correlation of corneal biomechanics in adult myopic patients after small incision corneal lens extraction (SMILE) based on the new generation of Corvis^® ST.This paper further demonstrates the value of CV in evaluating corneal biomechanical properties after SMILE and predicting the outcome of refractive surgery. Methods: A total of 72 cases (72 eyes) of adult myopia who were scheduled for SMILE in The Second People’s Hospital of Foshan from January to August 2021 were included in this prospective observational case study. To avoid binocular correlation, a suitable eye for each person was selected for inclusion. Based on the preoperative central corneal thickness (CCT), the cases were divided into a low corneal thickness group (470–<530 μm), a medium corneal thickness group (530–<560 μm), and a high corneal thickness group (≥560 μm). The biomechanical intraocular pressure (bIOP), DA ratiomax (2 mm) (DA2ratio), integrated inverse concave radius (IR), Ambrósio’s relational thickness (ARTh), stiffness parameter applanation 1 (SP-A1),corvis biomechanical index (CBI) and stress-strain index (SSI) were measured by Corvis^® ST. The Pentacam anterior segment analysis system was used to measure partial CV and total CV with a diameter of 3, 5, and 7 mm from the top of the cornea, with an assumed diameter of 10 mm. The changes in corneal biomechanical parameters and CV before SMILE and 3 months after SMILE were compared. The correlation between corneal biomechanical parameters and CV was studied. Data were analyzed by paired and independent sample t-tests. One-way analysis of variance (ANOVA) was used to assess the differences between the corneal thickness groups. Spearman correlation analysis and partial least squares linear regression (PLSLR) were used for correlation analyses. Results: Three months after SMILE, the CV in different areas (CV_3mm, CV_5mm, CV_7mm, and CV_10mm) were significantly lower than those before SMILE, and the differences were statistically significant (all P<0.001). The corneal biomechanical parameters bIOP, ARTh, SP-A1, and SSI were significantly decreased compared with those before the operation (P<0.05). In contrast, the DA2 ratio, IR, and CBI were significantly higher than those before the operation (P<0.05). A comparison of the corneal biomechanical parameters ARTh, SP-A1, DA2 ratio, IR, and CBI in the different corneal thickness groups before and after SMILE showed overall differences among the groups (P<0.05).However, there was no significant change in the SSI between the low and medium corneal thickness groups. The correlation of the preoperative baseline DA2ratio was negatively correlated with CV_3mm and CV_5mm, and positively correlated with CV_10mm; Conversely, ARTh was positively correlated with CV_3mm and CV_5mm, and negatively correlated with CV_10mm; BIOP was positively correlated with CV_10mm; IR was negatively correlated with CV_3mm and CV_5mm, and positively correlated with CV_10mm; SP-A1 was positively correlated with CV_3mm and CV_5mm, and negatively correlated with CV_10mm; CBI was negatively correlated with CV_3mm, CV_5mm, and CV_10mm, while SSI was positively correlated with CV_3mm and negatively correlated with CV_10mm (all P<0.05). At 3 months after SMILE, ARTh was positively correlated with CV_3mm and CV_5mm, and negatively correlated with CV_10mm; CBI was negatively correlated with CV_3mm, and positively correlated with CV_10mm (all P<0.05). Conclusion: This study demonstrated that at 3 months after SMILE, CV_3mm, CV_5mm, CV_7mm, CV_10mm, intraocular pressure, and CCT in the central and peripheral areas decreased significantly compared with to those before the operation, and the more peripheral the area, the more the CV decreased. Three months after SMILE, the new corneal biomechanical parameters of the new generation Corvis^® ST changed significantly compared to those before the operation, and there was a certain correlation between CV in different regions and corneal biomechanical parameters. It is expected that CV in different regions after SMILE can characterize some changes in corneal biomechanical properties after SMILE, and CV may become a parameter factor for characterizing and predicting the development of corneal dilatation.

随着科学技术的提高、手术方式的改进，角膜屈光手术成为治疗近视的主要方式。角膜屈光手术后角膜形态及生物力学的变化对于尽早发现术后相关并发症及术后长期稳定性具有重要意义，不同的术式及术后不同的恢复阶段角膜表面非球面参数及生物力学指标的变化存在一定差异，明确其变化的原因及机制可对临床研究提供一定的参考。

With the improvement of science and technology and the improvement of surgical methods, corneal refractive surgery has become the main way to treat myopia. The changes of corneal morphology and biomechanics after corneal refractive surgery are of great significance for early detection of postoperative complications and also affect the long-term stability after corneal refractive surgery. There are some differences in the changes of aspheric parameters and biomechanical properties in different surgical procedures and different postoperative recovery stages. Clarifying the reasons and mechanisms of these changes can provide some reference for clinical research.