Baron W S, Munnerlyn C
Visx Inc, Sunnyvale, Calif.
Refract Corneal Surg. 1992 Sep-Oct;8(5):355-62.
A duplex optical image is created when the ablation zone formed by excimer photorefractive keratectomy is smaller than the entrance pupil. Visual performance and secondary effects are analyzed using a theoretical model of the optical image.
A point-spread function having a centered in-focus component surrounded by an annular out-of-focus component is calculated from pupil size, ablation size, refractive error, and photoreceptor directional sensitivity. The line-spread, edge-spread, and optical transfer functions are derived.
In the line- and edge-spread functions, secondary maxima and curvilinear ramps are most evident with low refractive errors. The half-height widths of the point- and line-spread functions change little. The optical transfer function is reduced in proportion to the distribution of light between the image components.
Stable point and line half-height widths explain why Snellen visual acuity is insensitive to annular blur. Contrast sensitivity correlates with symptoms of haze and fog. Halos and ghost images are associated with secondary optical maxima and curvilinear ramps. Neither visual acuity nor contrast sensitivity can predict halos or ghost images. Halos and ghost images will be most prevalent in low illumination and for low refractive corrections. High refractive errors will produce fewer visual side effects than low refractive errors.
当准分子激光角膜切削术形成的消融区小于入瞳时，会产生双工光学图像。使用光学图像的理论模型分析视觉性能和次要效应。
根据瞳孔大小、消融大小、屈光不正和光感受器方向敏感性计算出一个点扩散函数，该函数具有一个位于中心的聚焦分量，周围环绕着一个环形离焦分量。推导出线扩散函数、边缘扩散函数和光学传递函数。
在线扩散函数和边缘扩散函数中，次要最大值和曲线斜坡在低屈光不正时最为明显。点扩散函数和线扩散函数的半高宽变化不大。光学传递函数与图像组件之间的光分布成比例降低。
稳定的点和线半高宽解释了为什么斯内伦视力对环形模糊不敏感。对比敏感度与雾状混浊的症状相关。光晕和重影图像与次要光学最大值和曲线斜坡有关。视力和对比敏感度都无法预测光晕或重影图像。光晕和重影图像在低光照条件下和低屈光矫正时最为普遍。高屈光不正产生的视觉副作用比低屈光不正少。
