角膜前、后表面像差在近视及近视散光人眼中的分布特点及补偿机制的初步研究

Distribution and compensation mechanism of aberrations between anterior and posterior surface of the cornea in myopia and myopic astigmatism eyes

目的 探讨近视及近视散光人群角膜前后表面像差的补偿机制及其与角膜表面曲率、眼压、中央角膜厚度（CCT）的相关关系.方法 随机选取近视及近视散光患者161例（300只眼）,应用Sirius三维眼前节分析系统测量以角膜顶点为中心直径为2、4、6mm区域内角膜前、后表面及整体角膜像差,计算二阶到七阶各像差及总高阶像差的补偿因子（CF）.并将其分为纯角膜散光和非纯角膜散光两组,比较两组间的CF.采用Mann-Whitney U检验进行不同像差及两组间CF的比较,采用Spearman相关分析各像差值与最平角膜曲率（K1）、最陡角膜曲率（K2）、眼压及CCT的相关性.结果 各像差均方根值随分析区域的增大而增大,二阶到七阶像差值随阶数的增大而减小.越向周边,以叠加为主,补偿机制所占的比例越低,而同一区域内,随着像差阶数的增高角膜前后表面像差逐渐由叠加机制向补偿机制转变.角膜中央区球差（Z40）表现为叠加,周边区表现为轻度的补偿机制;彗差（Z3±1）中央区（2mm）为补偿机制,但周边（6mm）无补偿;各分析区域下,角膜像散（Z2±2）CF接近于0,仅周边区表现为轻度的补偿;三叶草（Z3±3）始终表现为叠加,但越向周边,叠加作用逐渐减小;各个区域内角膜前后表面次级球差（Z60）均表现为补偿.左右眼在不同区域下角膜前后表面各像差的补偿作用基本相同.角膜Z2±2、Z3±4、Z40与角膜K1、K2均有不同程度的相关性.整体角膜6 mm区域内彗差（Z3±1）和球差（Z40）与眼压呈负相关（r彗差=-0.188,P＜0.05;r球差=-0.147,P＜0.05）,不同区域下不同位置各像差与CCT均无明显相关性（P＞0.05）.结论 角膜中央区像差主要以补偿为主,越向周边,补偿所占的比例逐渐减低.角膜前后表面像散和球差在周边区表现为轻度的补偿作用,或许有益于夜间视觉质量的提高.角膜像差与角膜曲率、眼压均有一定的相关性,在周边区域（6 mm）,眼压越高,球差及彗差相对越小.

Objective To study the compensation mechanism of aberrations between anterior and posterior corneal surface,and to investigate the correlations between corneal aberrations and K values,intraocular pressure and central corneal thickness.Methods One hundred and sixty-one subjects （300 eyes） with myopia and myopic astigmatism were recruited randomly.Corneal aberrations （anterior,posterior and total） in three different optical zones （2 mm,4 mm,and 6 mm） centered on the corneal vertex were assessed with a corneal topographer （Sirius）.We also calculated compensation factors （CFs） as a measure of the relative efficiency of the aberration compensation mechanism.Astigmatism was divided into corneal astigmatism and non-corneal astigmatism.Mann-Whitney U test was utilized for the comparison of different aberrations and CFs between the two astigmatism groups.Spearman correlation was applied to analyze the correlations between corneal aberrations and K values,intraocular pressure and central corneal thickness.Results As the order of the aberrations elevated from the second to the seventh,the RMS values decreased significantly.The larger the optical zone,the greater the values of aberrations and the lower the percentage of the compensation mechanism among all the Zernike terms.At the same time,as the order of the aberrations increased,the predominance of the compensation mechanism was increasingly obvious.Slight compensation of spherical aberration （Z40） was observed in the peripheral.In the center of the analyzing zones （2 mm）,compensation mechanism represented in coma （Z3±1）,and it disappeared in the peripheral.We detected slight compensation of the corneal astigmatism （Z2±2） in the surrounding zone,although the compensation factors were closed to zero in diverse optical zones.Superposition was found in trefoil （Z3±3） straightly.Nevertheless,a tendency towards compensation was discovered with the enlargement of the optical zones.And the secondary spherical aberration （Z60） behaved compensation continuously.However,similar compensation was discovered between the right eye and left eye in different analyzing optical zones.There were significant correlations between the flattest K values and Z2±2,Z3±3and Z40 in the anterior,posterior and total cornea.It was similar with the steepest K values.When the optical zone expanded to 6 mm,Z3±1 and Z40 significantly decreased with intraocular pressure （rcoma=-0.188,P〈0.05.rspherical=-0.147,P〈0.05）.No correlation was found between various aberrations and central corneal thickness （P〉0.05）.Conclusions Compensation dominated in the corneal center,while the percentage decreased gradually as the optical zone extended.Slight compensation in astigmatism and spherical aberration between the anterior and posterior cornea may be benificial to the scotopic visual quality.Corneal aberrations were significantly related to K values and intraocular pressure.