BIFOCAL LENSES MAY PREVENT TRANSIENT TASK-INDUCED FAR POINT SHIFTS

Mark Rosenfield

Abstract

Previous investigations have demonstrated a small but significant transient myopic shift in the far point of accommodation (FP) following periods of sustained near-vision. The aim of the present study was to investigate the effect of varying the amount of blur-driven accommodation during the course of a near-vision task. Accordingly, 9 visually-normal subjects were required to perform a 20min near-vision task at a viewing distance of 25cms. Pre- and post-task measurements of the FP were recorded objectively using an open-field infra-red optometer (Canon Autoref R-1). The near-task was viewed monocularly through: i) the habitual distance refractive correction, ii) a +2.00D near addition, iii) a +4.00D near addition, iv) a 0.5mm pinhole. The mean post-task FP shifts observed for the 4 conditions were +0.28D, +0.17D, +0.01D and +0.15D, respectively. These results demonstrate that reducing the accommodative stimulus significantly diminishes the magnitude of the transient task-induced FP shift. However, the within-task accommodative requirement must be eliminated entirely, rather than merely reduced, in order to minimize any post-task FP change. In addition, the result obtained with pinhole viewing suggests that accommodation stimulated by factors other than optical blur (e.g., proximally-induced accommodation) can also produce transient FP shifts. Accordingly, the task-induced change in FP appears to be related to the magnitude, but not necessarily the composition of the overall within-task accommodative response.

Details

Year: 1992

Program Number: 1:15 pm

Author Affiliation: n/a

Co-Authors: B.Sc. (Optom), Margaret Gillard, Kenneth Ciuffreda

Co-Author Affiliation: n/a

Room: Scotland A