Differences in the accommodation stimulus response curves of adult myopes and emmetropes.

While the accommodation system has been implicated in myopia development, the nature of this relationship remains obscure. This study investigated the differences in accommodation stimulus response curves between adult myopes and emmetropes. Myopic subjects were classified according to age of onset and stability of their myopia. Accommodation stimulus response curves were measured using three different methods: (i) real targets presented at viewing distances of 4 m to 0.25 m, (ii) a target at 4 m viewed through negative lenses of increasing power, and (iii) a target at 0.25 m viewed through positive lenses of decreasing power. A Canon Autoref R-1 measured the accommodation responses at 5 levels of demand (increasing from 0 D to 4 D in 1 D steps). We found significant differences between the three methods used to stimulate an accommodation 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 differences between early-onset myopes, late-onset myopes and emmetropes were not observed, we did observe differences when myopic subjects were reclassified according to whether their myopia was progressing or stable. A reduced accommodation response to negative lens-induced accommodative demand was found in progressing myopes but not in stable myopes. These results provide further evidence for the link between myopia progression and inaccurate accommodation. The data also suggest that adult myopes with stable refractive errors show accommodation responses similar to that of emmetropes.