近视眼角膜非球面参数分布特征

Research on distribution characteristics of corneal asphericity of myopic eyes

目的 研究近视准分子激光人群术前角膜前后表面非球面参数（Q值）的分布特征,为临床诊疗提供理论基础.方法 前瞻性研究.应用基于Scheimpflug照相原理的Pentacam HR眼前节测量及分析系统对75例近视患者右眼进行测量,患者分为低度角膜散光组（前表面散光＜＋1.00 D）和中高度角膜散光组（前表面散光≥＋1.00 D）,系统分析角膜前后表面平均Q值分布特征,角膜中央不同角度范围Q值分布特征,上方、下方、鼻侧及颞侧半子午线上Q值分布特征.2组间比较采用独立样本t检验,各组内Q值间比较采用单因素方差分析.结果 该75例角膜中央30°范围平均Q值前表面为-0.17±0.09,后表面为-0.02±0.16.角膜前表面2组不同角度范围平均Q值均小于0,且2组对应角度范围内Q值间差异无统计学意义,2组内不同角度范围平均Q值间差异有统计学意义（F=6.340、9.963,P＜0.01）,2组Q20均大于Q30及Q25且差异具有统计学意义（P＜0.05）,Q30及Q25之间差异无统计学意义.角膜后表面Q30趋近于0,Q25及Q20均大于0,Q30＜Q25＜Q20,且差异均具有统计学意义（F=54.614,P＜0.01）.角膜前表面2组不同半子午线上平均Q值均为负且2组对应半子午线上平均Q值间差异无统计学意义,2组不同半子午线上平均Q值间差异有统计学意义（F=19.262、31.935,P＜0.01）.低度角膜散光组QN30小于Q130、QS30及QI30,且差异均具有统计学意义（P＜0.05）,QT30、QS30及QI30之间差异均无统计学意义（P＞0.05）.中高度角膜散光组QS30及Q130之间差异无统计学意义（P＞0.05）,QN30＜QT30且QN30及QT30小于QS30及Q130,差异均具有统计学意义（P＜0.05）.角膜后表面QS30趋近于0,QI30为正,QN30及QT30为负,不同半子午线上平均Q值间差异有统计学意义（F=31.750,P＜0.01）,其中QT30及QS30之间差异无统计学意义（P＞0.05）,QN30＜QT30且QS30＜QI30,差异均具有统计学意义（P＜0.05）.结论 近视人群角膜前表面形态由中央到周边逐渐变平坦,后表面由中央到周边逐渐变陡峭.随角度范围的变大,角膜前表面变平坦的速率加快,后表面变陡峭的速率减慢.前表面各半子午线方向均为长椭圆形,从中央到周边其表面均逐渐变平坦.角膜前表面散光的大小未影响角膜前表面的形态.后表面上下方半子午线方向为扁椭圆形,鼻颞侧半子午线方向为长椭圆形。

Objective To evaluate the distribution characteristics of the asphericity （Q-value） of the corneal surfaces in a Chinese population who were candidates for excimer laser surgery; to provide some theoretical bases for clinical diagnosis and treatment.Methods This was a perspective study.Using the Pentacam HR measuring and analyzing system based on Scheimpflug photography,the right eyes of 75 Chinese myopes were evaluated for excimer laser surgery.Patients were divided into a low corneal astigmatism （〈＋1.00 D） group and a medium-high corneal astigmatism （≥＋1.00 D） group according to the anterior corneal surface astigmatism.The analysis was based on the distribution characteristics of the mean Q-values of both the anterior and posterior corneal surfaces and the distribution characteristics of the Q-value at different angles （20°,25° and 30°） and along different semi-meridians （superior,inferior,nasal and temporal）.Single factor analysis of variance was used to determine if there was a difference among Q-values within a particular group.The differences between the two groups were analyzed by an independent samples t-test.Results The mean Q-values of the 30° angle in Chinese myopes evaluated for excimer laser surgery were-0.17±0.09 and-0.02±0.16 on the anterior and posterior corneal surfaces,respectively.The mean Q-values of the anterior corneal surface at different angles were negative and there was no statistically significant difference between the low corneal astigmatism group and medium-high corneal astigmatism group.There was a significant difference between the Q-values of the 2 groups at different angles （F=6.340,9.963,P〈0.01）,and in both groups Q20 was significantly larger than Q30 and Q25 （P〈0.05） but there was no statistically significant difference between Q30 and Q25.The mean Q-values of the posterior corneal surface were positive at the 20° and 25° angles and approached zero at the 30° angle.Comparisons between the 3 angles showed statistically significant differences （F=54.614,P〈0.01）.The comparisons showed that Q30〈Q25〈Q20.All mean Q-values along different semi-meridians of the anterior corneal surface were negative and there was no statistically significant difference between the 2 groups.There was a significant difference between Q-values along different semi-meridians in the 2 groups （F=19.262,31.935,P〈0.01）.In the low corneal astigmatism group,QN30 was significantly smaller than QT300,QS30 and QI30 （P〈0.05） but there was no statistically significant difference between QT30,QS30 and Q130 （P〉0.05）.In the medium-high corneal astigmatism group,QT30 was significantly bigger than QN30 （P〈0.05） but there was no statistically significant difference between QS30 and Q130 In addition,QN30 and QT30 were significantly smaller than QS30 and Q130 （P〈0.05）.The Q-values of the posterior surface were positive along the inferior semi-meridian,negative along the nasal and temporal semi-meridians,and approached zero along the superior semi-meridian.There was also a significant difference between Q-values along different semi-meridians on the posterior surface （F=31.750,P〈0.01）.There were statistically significant differences between QT30 and QN30 （P〈0.05） and Q130 and QS30 （P〈0.05）.Comparisons showed that QT30〉QN30 and QS30〉QS30,but there was no statistically significant difference between QT30 and QS30.Conclusion The curvature along the anterior corneal surface becomes flatter from the center to the periphery,while it becomes steeper from the center to the periphery at the posterior corneal surface.The rate of the flattening of the anterior corneal surface increased as the range of the angle increased,while the rate decreased as the posterior corneal surface decreased.All the shapes on the anterior surface along different semi-meridians were long ovals.Corneal astigmatism does not affect corneal shape.The shapes of the posterior surface along the superior and inferior semi-meridians were short ovals,but were long ovals along the nasal and temporal semi-meridians.