散光对正常人眼角膜前表面调制传递函数的影响

An analysis of the influence of astigmatism on the modulation transfer function of the normal human anterior corneal surface

目的 用调制传递函数（MTF）客观分析散光对正常人眼角膜前表面光学质量的影响.方法 回顾性系列病例研究.角膜前表面4 mm直径范围顺规散光456例（907眼）,依散光度分为A（散光度≤0.50 D）、B（0.50 D＜散光度≤1.00 D）、C（1.00 D＜散光度≤2.00 D）、D（2.00 D＜散光度≤3.00 D）、E（散光度＞3.00 D）5组;逆规散光19例（22眼）.用Sirius角膜地形图眼前节分析仪模拟角膜前表面中央4 mm直径范围垂直和水平子午线方向的MTF曲线,从曲线上可以得到5、10、15、20、25、30、35、40、45、50、55、60 c/d空间频率的MTF值,不同散光度同一频率下的MTF值的比较采用完全随机设计资料的方差分析,同一频率下垂直子午线的MTF值与水平子午线的MTF值比较采用配对资料t检验.结果 顺规散光组：（①随着散光度增大,水平和垂直子午线方位的MTF值均逐渐降低,散光度越大,降低的幅度越明显;②相同散光度组中垂直子午线各个频率的MTF值均低于水平子午线,差异有统计学意义;③不管是水平子午线还是垂直子午线,散光值对高频的影响最大,其次是中频,对低频部分影响较小.逆规散光组：垂直子午线各个频率的MTF值均高于水平子午线,差异有统计学意义.结论 角膜散光对角膜前表面不同方位（垂直和水平子午线）的MTF值均有明显影响.

Objective To use the modulation transfer function （MTF） to objectively analyze the influence of astigmatism on the optical quality of the normal human anterior corneal surface.Methods In this retrospective caseseries study,456 patients （907 eyes） who had with-the-rule astigmatism were divided into five groups according to the degree of astigmatism：A（astigmatism ≤0.50 D）,B（0.50 D＜ astigmatism ≤1.00 D）,C（1.00 D＜ astigmatism ≤2.00 D）,D（2.00 D＜ astigmatism ≤3.00 D）,E（astigmatism ＞3.00 D）.Nineteen patients （22 eyes） had against-the-rule astigmatism.A Sirius corneal topography analyzer was used to measure the optical quality of the anterior corneal surface and describe the vertical meridians and horizontal meridians on MTF curve for a 4 mm diameter pupil.The MTF values at different spatial frequencies （5,10,15,20,25,30,35,40,45,50,55,60 c/d） were obtained from the MTF curves.The MTF values for different degrees of astigmatism at the same frequency were compared by complete randomized analysis of variance,and the MTF values of the vertical and horizontal at the same frequency were compared by a paired t test.Results With-the-rule astigmatism：①The MTF values of the vertical and horizontal meridians decreased as the degree of astigmatism increased.The decreasing span was more obvious with a greater degree of astigmatism.②The MTF value of the horizontal meridian was higher than that of the vertical meridian in each group with the same degree of astigmatism （P＜0.05）.③Whether the meridian was vertical or horizontal,astigmatism had the most influence on high frequencies,followed by intermediate frequencies,with the least influence on low frequencies.Against-the-rule astigmatism：the MTF value of the vertical meridian was higher than that of the horizontal meridian （P＜0.05）.Conclusion Corneal astigmatism has a significant influence on the vertical and horizontal meridians of the modulation transfer function on normal human anterior corneal surfaces.