Retinal image quality in the human eye as a function of the accommodation

The changes in the retinal image quality with accommodation in the human eye were studied by using a near-infrared double-pass apparatus. A slightly better modulation transfer function (MTF) in the unaccommodated eye with respect to the accommodated eye was found when using an artificial pupil with a fixed diameter. The technique allows the estimation of the MTF of the accommodated eye discounting the effect of the accommodative defocus error. Most of the reduction found in the MTF with accommodation could be explained in terms of the accommodative defocusing error. However, the shape of the retinal images clearly changes with accommodation, indicating that other aberrations are also altered with accommodation. In general, the double-pass image for the accommodated eye tends to be more symmetric than that of the unaccommodated eye. This is probably due to either a decrease in the amount of coma-like aberrations with accommodation or to an increase of other symmetric aberrations, such as defocus or spherical aberration, that hide the asymmetries present in the retinal image of the unaccommodated eye.