应用CorVis ST对圆锥角膜及亚临床期圆锥角膜生物力学特性的研究及判别标准分析

Examination and discriminant analysis of corneal biomechanics with CorVis ST in keratoconus and subclinical keratoconus

目的:应用可视化角膜生物力学分析仪(comeal visualization Scheimpflug technology,CorVis ST)对圆锥角膜、亚临床期圆锥角膜及正常角膜的生物力学参数进行检测,比较三者的参数差异,探讨生物力学参数对圆锥角膜和亚临床期圆锥角膜的判别价值。方法:收集2015年10—12月在北京大学第一医院眼科就诊的圆锥角膜患者17例(24只眼)、亚临床期圆锥角膜患者12例(12只眼),同时选取正常志愿者40例(40只眼)。用CorVis ST对三组患者角膜力学特性进行分析,比较三组患者的角膜生物力学参数差异,对各个参数对疾病的区分度进行评价。以力学参数、眼内压、角膜中央厚度为指标,建立判别分析函数,并评价角膜力学参数对判别函数的贡献。结果:圆锥角膜、亚临床期圆锥角膜和正常角膜的生物力学性能依次递增,除第二压平时间、最大压陷时间和第一次压平速度外,其他指标反映出的差异均有统计学意义(P<0.05);最大压陷时角膜曲率半径和角膜中央厚度可以反映出三组角膜之间的两两差异,较好地体现出圆锥角膜不同病程的力学状态。建立典则判别函数,可反映三组角膜的差别,回判准确率约85%,其中,对判别函数贡献较大的力学参数指标为角膜中央厚度、最大压陷时角膜曲率半径、最大压陷深度和第二次压平速度。结论:与正常角膜相比较,亚临床期圆锥角膜和圆锥角膜的生物力学性能依次下降。基于CorVis ST的力学参数指标可以区分出圆锥角膜、亚临床期圆锥角膜和正常角膜。

Objective:To compare the corneal biomechanical properties among keratoconus,subclinical keratoconus and normal corneas by using CorVis ST,and to estimate the effect of these biomechanical indices in discriminating keratoconus and subclinical keratoconus from normal.Methods:A total of 76 eyes of 67 subjects were enrolled and divided into three groups.Keratoconus group included 24 eyes from 17 patients,subclinical keratoconus group included 12 eyes from 12 patients and normal group included 40 normal eyes from 40 subjects.All the eyes were assessed with CorVis ST and ten biomechanical para-meters,intraocular pressure(IOP)and central corneal thickness(CCT)were obtained from this machine.The discrimination of biomechanical characteristic of the three groups based on the all indices was reflected by discriminant analysis and the Fisher discriminant function was established.Results:The values of corneal biomechanics of keratoconus,subclinical keratoconus,normal eyes were increased in sequence,except for three indices:the second applamation time(A2T),time taken to reach highest concavity(HCT)and maximum corneal velocity during the first applanation(Vin).Three sets of data were among a statistically significant difference(P<0.05).There were statistically significant differences(P<0.05)between any two groups by comparing with such two indices:radius value of central concave curvature at highest concavity(HCR)and CCT.The grades of the three groups were obvious,evaluated by the discriminant function.The accuracy of reevaluation was 85%by validation method.The biggest contribution of indices in discriminant function was given by such four indices in sequence:CCT,HCR,maximum deformation amplitude of highest concavity(HCDA)and maximum corneal velocity during the second applanation(Vout).Conclusion:The corneal biomechanical properties of keratoconus and subclinical keratoconus were decreased compared with normal eyes.The biomechanical parameters based on CorVis ST showed a good performance for discriminating among keratoconus,subclinical keratoconus and normal corneas.