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.

Hema Radhakrishnan and W. Neil Charman
Faculty of Life Sciences
Moffat Building, University of Manchester
PO Box 88, Sackville Street
Manchester M60 1QD, UK