Changes in astigmatism with accommodation


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An experiment is described in which changes in ocular astigmatism were recorded over an accommodation stimulus range of 0–4 D, in the right eyes of a group of 31 normal subjects aged 17–37 years. The visual axes were horizontal and the observation conditions were monocular. Although subjects had a range of spherical ametropia, all had initial astigmatism of 1.0 DC or less. It was found that, for most subjects in the group, astigmatism changed in the with-the-rule direction, the mean change being −0.036 DC at axis 176 deg for each dioptre of accommodation response. It is speculated that these changes might reflect increases in lens tilt about a horizontal axis, caused by the combined effects of a slacker zonule and gravity.