Marcos S, Navarro R
Instituto de Optica Daza de Valdés, Consejo Superior de Investigaciones Científicas, Madrid, Spain.
J Opt Soc Am A Opt Image Sci Vis. 1997 Apr;14(4):731-40. doi: 10.1364/josaa.14.000731.
We have developed a high-resolution imaging technique, based on speckle interferometry, for the objective determination of the cone spacing in the living human fovea. The spatial resolution attained with this technique is theoretically diffraction limited by the pupil size. However, the highest frequency that we measure varies greatly among subjects, especially for fully dilated pupils. We have conducted several experiments (determination of the cutoff frequency of ocular speckle interferometry, the double-pass modulation transfer function, and the Stiles-Crawford effect) that indicate that, as expected, the resolution is not limited by the incoherent modulation transfer function. We found, though, a high correlation between the cutoff frequency and the width of the eye's Stiles-Crawford function. This implies that the resolution depends on the structural properties of the cone mosaic itself. In addition, we have compared the Nyquist frequency of the cone mosaic, determined objectively by our technique, with the grating visual acuity measured in the same eyes at the same foveal eccentricities. For our subjects, visual resolution nearly matches the Nyquist frequency within the fovea, except at the foveal center, where the optical transfer function of the eye attenuates the contrast of frequencies close to the Nyquist limit to a value below threshold.
我们基于散斑干涉测量法开发了一种高分辨率成像技术，用于客观测定活体人眼中央凹处视锥细胞的间距。该技术所达到的空间分辨率在理论上受瞳孔大小的衍射限制。然而，我们测量到的最高频率在不同受试者之间差异很大，尤其是对于完全散瞳的情况。我们进行了多项实验（测定眼散斑干涉测量法的截止频率、双程调制传递函数以及斯泰尔斯 - 克劳福德效应），这些实验表明，正如预期的那样，分辨率不受非相干调制传递函数的限制。不过，我们发现截止频率与眼睛斯泰尔斯 - 克劳福德函数的宽度之间存在高度相关性。这意味着分辨率取决于视锥细胞镶嵌结构本身的结构特性。此外，我们将通过我们的技术客观测定的视锥细胞镶嵌结构的奈奎斯特频率，与在相同眼睛的相同中央凹偏心率下测量的光栅视力进行了比较。对于我们的受试者，除了在中央凹中心处，视觉分辨率在中央凹内几乎与奈奎斯特频率匹配，在中央凹中心处，眼睛光学传递函数将接近奈奎斯特极限的频率对比度衰减到阈值以下的值。
