Accommodative error, adaptation and myopia

Accommodative adaptation, resulting from the sustained output of slow blur- driven accommodation during the course of a sustained near-vision task, has generally been assessed under open-loop conditions. This study examined wh ether adaptation influences closed-loop accommodation during the course of a sustained near-vision task. Accommodative adaptation was assessed in 18 f ully-corrected subjects by comparing pre- and post-task values of dark acco mmodation recorded objectively with an infra-red optometer. Subjects perfor med a continuous 10 min binocular near-vision task at a viewing distance of 33 cm, with the within-task accommodative response being assessed at 1 min intervals during this period. Subjects were categorized into adaptors (N = 11) and non-adaptors (N = 7) on the basis of whether their initial 10 sec post-task adaptation exceeded +0.30D. The adapting group exhibited a signif icant decline in the lag of accommodation during the first 3 min of the nea r-task, whereas no significant change in the within-task response over time was observed in the non-adapting group. These results indicate that accomm odative adaptation increases the accuracy of the within-task, closed-loop a ccommodative response. Furthermore, we speculate that a deficit in accommod ative adaptation, being accompanied by increased retinal defocus during nea r fixation, may contribute to the development of nearwork-induced myopia. ( C) 1999 The College of Optometrists. Published by Elsevier Science Ltd. All rights reserved.