Charman W N, Voisin L
School of Optometry, University of Waterloo, Ontario, Canada.
Ophthalmic Physiol Opt. 1993 Jan;13(1):73-81. doi: 10.1111/j.1475-1313.1993.tb00429.x.
The variation with accommodation in the dimensions of the geometrical blur ellipse that is formed on the retina of the astigmatic eye is explored in relation to orientation dependence of the corresponding line-spread function (LSF) and modulation transfer function (MTF). It is shown that if theta is the orientation of the line or grating with respect to the more powerful meridian of an eye having C dioptres of astigmatism, the optimal accommodation response varies as 0.5 C cos2 theta. The analysis is extended to include the effects of diffraction. Even at optimal focus, the diffraction-limited MTF at 45 degrees to the principal meridians of an eye with small amounts of astigmatism is substantially degraded. For example, with a 3 mm pupil and only 0.50 DC of astigmatism, the first zero in monochromatic modulation transfer at 555 nm occurs at approximately 32 c/deg in the oblique meridian as compared with 94 c/deg in the principal meridians. The results are used as the basis of a discussion of the possible role of infant and juvenile astigmatism in the development of the oblique effect and of meridional amblyopia.
探讨了散光眼视网膜上形成的几何模糊椭圆尺寸随调节的变化，这与相应的线扩散函数（LSF）和调制传递函数（MTF）的方向依赖性有关。结果表明，如果θ是线或光栅相对于具有C屈光度散光的眼睛的较强子午线的方向，则最佳调节反应随0.5Ccos²θ变化。分析扩展到包括衍射效应。即使在最佳聚焦时，少量散光眼的与主子午线成45度角处的衍射极限MTF也会显著降低。例如，对于3mm的瞳孔和仅0.50DC的散光，在555nm处的单色调制传递中，斜子午线处的第一个零点出现在约32c/deg，而在主子午线处为94c/deg。这些结果被用作讨论婴幼儿散光在斜视效应和子午线弱视发展中可能作用的基础。
