Myopes of low degree commonly report that their vision seems poorer upon removal of their spectacles compared to that after a period without spectacle wear. Notably, this difference in vision can he appreciated after distance fixation. In this paper, we propose and test several alternative hypotheses to explain the phenomenon: an accommodative response to spectacles, sensory adaptation, or altered criteria for blur of psychological origin. We measured visual acuity (VA), refractive error, and lens thickness on 10 subjects with less than 2.00 D of myopia. Testing was performed after two 90-min sessions viewing at distance. At one session, the subjects wore their current spectacle correction and, at the other session, no correction was worn. VA underwent a slight but significant decrease (0.4 of a line) after the session in which spectacles were worn, but no difference in refractive error or lens thickness was found. The change in acuity in the absence of a refractive shift suggests sensory adaptation to blur. However, the demonstrated change in VA appears to be less than that which is subjectively reported; accordingly, psychological input cannot be ruled out.

KONRAD PESUDOVS*
NOEL A. BRENNAN†
Department of Optometry, University of Melbourne, Parkville, Australia

* Optometrist.
† Optometrist, Ph.D., Member of Faculty, F.A.A.0.

Accepted for publication: February 22, 1993

Key words: myopia, adaptation, accommodation, spectacle wear, blur