DIFFERENCES IN THE ACCOMMODATION STIMULUS-RESPONSE CURVES OF ADULT MYOPES AND EMMETROPES

While the accommodation system has been implicated in myopia developme nt, the nature of this relationship remains obscure. This study invest igated the differences in accommodation stimulus response curves betwe en adult myopes and emmetropes. Myopic subjects were classified accord ing to age of onset and stability of their myopia, Accommodation stimu lus response curves were measured using three different methods: (i) r eal targets presented at viewing distances of 4 m to 0.25 m, (ii) a ta rget at 4 m viewed through negative lenses of increasing power, and (i ii) a target at 0.25 m viewed through positive lenses of decreasing po wer, A Canon Autoref R-l measured the accommodation responses at 5 lev els of demand (increasing from 0 D to 4 D in 1 D steps), We found sign ificant differences between the three methods used to stimulate an acc ommodation response in all subject groups, for example, accommodation lags at high accommodative demands were greatest for the negative lens series and least for the positive lens series. In addition, while dif ferences between early-onset myopes, late-onset myopes and emmetropes were not observed, we did observe differences when myopic subjects wer e reclassified according to whether their myopia was progressing or st able, A reduced accommodation response to negative lens-induced accomm odative demand was found in progressing myopes but not in stable myope s. These results provide further evidence for the link between myopia progression and inaccurate accommodation. The data also suggest that a dult myopes with stable refractive errors show accommodation responses similar to that of emmetropes. (C) 1998 The College of Optometrists. Published by Elsevier Science Ltd.