The effect of defocus on the contrast and phase of the retinal image of a sinusoidal grating.
The variation with defocus in the contrast and phase of the retinal image of a grating stimulus is computed from a knowledge of the measured wavefront aberration of individual eyes. Contrast or modulation transfer is generally lower than in the aberration-free, diffraction-limited case, even at a pupil size of 3 mm, and marked spatial phase shifts, which can be seen as sideways shifts in the retinal image, frequently occur. A simple demonstration of these effects is given. The possible significance of the focus-dependent spatial phase shifts for the phase discrimination of the visual system and accommodation is discussed.
Walsh
G
G
Department of Optometry and Vision Sciences, University of Manchester Institute of Science and Technology, UK.
Charman
W N
WN
D000065:Accommodation, Ocular / Q000502:physiology*; D015350:Contrast Sensitivity / Q000502:physiology*; D006801:Humans; D007498:Iris / Q000502:physiology; D012160:Retina / Q000502:physiology*