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Effect of Size of Pupil on Visual Acuity

Naturevolume 187pages11211123 (1960) | Download Citation



DENTON1 has suggested that a possible function of the pupil light reflex might be to provide apertures optimum for visual acuity at different light intensities. At low levels of luminance visual acuity is probably limited by the rate at which light quanta activate the retinal receptors2, and thus a large pupil admitting the maximum amount of light would appear to be advantageous. As the luminance is increased into the photopic range, loss of image contrast due to optical aberrations, diffraction, and stray light also tend to limit visual acuity, although the fineness of the retinal cone mosaic may ultimately become the limiting factor. The decrease in pupil size which normally accompanies increase of illumination should reduce to some extent the deleterious effects on visual acuity of the optical aberrations. However, it has never been shown that the actual response of the pupil reflex to a given steady luminance does in fact result in an aperture giving maximum spatial resolution at this luminance. It was therefore decided to determine experimentally whether an optimum aperture existed at each luminance-level, by measuring the relations between pupil size, luminance, and visual acuity over a wide range.

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    • A. H. GREGORY

    Present address: Department of Psychology, University of Hull,


  1. Physiological Laboratory, University of Cambridge

    • F. W. CAMPBELL
    •  & A. H. GREGORY


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