The Dependence of Spatial Aliasing on the Amount of Defocus and Spherical Aberration in a Model Eye

The performance of the human eye is limited not only by optical factors but also capabilities of signal processing. The maximum spatial frequency that can be reliably processed depends on the sampling rate. If this frequency is exceeded, spatial aliasing occurs. In this study, we investigate the optimum amount of defocus and spherical aberration needed to avoid spatial aliasing. Measurements are carried out using a simple model eye with the optical and geometrical parameters close to those of a living human eye. A checkerboard pattern with the spatial frequency of 60 cycles/degree is used as a stimulus. A deformable mirror was used to control the amount of defocus and spherical aberration from 0 µm to 0.50 µm in steps of 0.05 µm. If the amount of aberrations is low, fringes of aliased signals are visible along the direction 35.5 degrees relative to the vertical edge of the image. This direction is close to the diagonal direction along which the sampling rate is the lowest. When the amount of aberrations reaches 0.45 µm, spatial aliasing is not observed. The results suggest that low amount of ocular aberrations is desired.