Howland H C
Am J Optom Physiol Opt. 1985 Sep;62(9):621-5.
Recent photographic studies have generated renewed interest in the optics of the retinoscopic (skiascopic) image. In photoretinoscopy the subject's eye is illuminated by a point source of light and the fundal image of this light at the plane of the subject's pupil is observed or photographed from a position near the source. The image so obtained is a function of the dioptric defocus of the eye relative to the camera, D, the distance of the source and camera from the eye, A, the radius of the subject's pupil, R, and the distance of the point source from the edge of the camera aperture, E. The fraction of the subject's pupil which is not filled with light is termed the "Dark Fraction" (DF) and may be computed from a simple ray tracing model of the eye. It is given in terms of the above parameters by the equation DF = E/(2ARD). The validity of this equation was tested with a photoretinoscope and artificial eye. The photoretinoscope, which is a novel modification of an isotropic photorefractor, is also described.
近期的摄影研究重新引发了人们对视网膜检影（视网膜镜检查）图像光学的兴趣。在光视网膜检影中，受试者的眼睛由一个点光源照亮，并且从靠近光源的位置观察或拍摄该光在受试者瞳孔平面处的眼底图像。如此获得的图像是眼睛相对于相机的屈光性散焦D、光源和相机到眼睛的距离A、受试者瞳孔半径R以及点光源到相机光圈边缘的距离E的函数。受试者瞳孔中未被光充满的部分称为“暗区比例”（DF），可以通过眼睛的简单光线追踪模型计算得出。根据上述参数，它由公式DF = E/(2ARD)给出。使用光视网膜检影镜和人工眼对该公式的有效性进行了测试。还介绍了作为各向同性验光仪的一种新型改进的光视网膜检影镜。
