McLellan J S, Prieto P M, Marcos S, Burns S A
Schepens Eye Research Institute and Harvard Medical School, 20 Staniford Street, Boston, MA 02114, USA.
Vision Res. 2006 Sep;46(18):3009-16. doi: 10.1016/j.visres.2006.03.005. Epub 2006 May 12.
Wave aberrations degrade the optical quality of the eye relative to the diffraction limit, but there are situations in which having slightly aberrated optics can provide some relative visual benefits. This fact led us to consider whether interactions among aberrations in the eye's wavefront produce an advantage for image quality relative to wavefronts with randomized combinations of aberrations with the same total RMS error. Total ocular wave aberrations from two experimental groups and corneal wave aberrations from one group were measured and expressed as Zernike polynomial expansions through the seventh-order. In a series of Monte Carlo simulations, modulation transfer functions (MTFs) for the measured wave aberrations were compared to distributions of artificial MTFs for wavefronts created by randomizing the sign or orientation of the aberrations, while maintaining the RMS error within each Zernike order. In a control condition, "synthetic" model eyes were produced by choosing each individual aberration term at random from individuals in the experimental group, and again MTFs were compared for original and randomized signs. Results were summarized by the MTF ratio: real MTF/mean simulated MTF, as a function of spatial frequency. For a 6mm pupil, the mean MTF ratio for total ocular aberrations was greater than 1.0 up to 60 cycles per degree, suggesting that the eye's aberrations are not independent and that there may be a positive functional consequences to their interrelations. This positive relation did not hold for corneal aberrations alone, or for the synthetic eyes.
波像差相对于衍射极限会降低眼睛的光学质量，但在某些情况下，具有轻微像差的光学系统可能会带来一些相对的视觉益处。这一事实促使我们思考，与具有相同总均方根误差的随机组合像差的波前相比，眼睛波前中的像差之间的相互作用是否会对图像质量产生优势。测量了两个实验组的全眼波像差和一个组的角膜波像差，并通过七阶泽尼克多项式展开来表示。在一系列蒙特卡洛模拟中，将测量像差的调制传递函数（MTF）与通过随机改变像差的符号或方向而创建的波前的人工MTF分布进行比较，同时保持每个泽尼克阶内的均方根误差。在一个对照条件下，通过从实验组个体中随机选择每个单独的像差项来生成“合成”模型眼，并且再次比较原始和随机符号的MTF。结果通过MTF比率进行总结：实际MTF/平均模拟MTF，作为空间频率的函数。对于6mm的瞳孔，全眼像差的平均MTF比率在每度60周之前大于1.0，这表明眼睛的像差不是独立的，并且它们之间的相互关系可能会产生积极的功能后果。这种正相关关系单独对于角膜像差或合成眼并不成立。
