近视眼角膜非球面参数分布特征

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

Research on distribution characteristics of corneal asphericity of myopic eyes

ObjectiveTo 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. MethodsThis 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. ResultsThe 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 Q30QN30 and QI30>QS30， but there was no statistically significant difference between QT30 and QS30. ConclusionThe 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.