Abstract
Changes in scotopic acuity as a function of varying states of natural accommodation have been measured with targets at various distances and luminances. Results for two observers showed that the amounts of negative accommodation needed to produce maximum acuity increased with decreasing luminance or increasing target distance at a constant luminance. The amount of natural negative accommodation needed for maximum acuity was much less than has been found with the use of spectacles and natural accommodation for infinity. There appeared to be a critical luminance level at which changes in accommodation produced minimal changes in acuity. The effect of red vs white fixation lights was also investigated.
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