Repeatability of post‐task regression of accommodation in emmetropia and late‐onset myopia

The characteristics of post‐task regression of accommodation to pre‐task ionic accommodation (TA) levels have been examined in a number of studies to clarify the nature of the within‐task facility for accommodative adaptation. Of special interest is the recent observation that significant attenuation of post‐task regression occurs in late‐onset myopes (LOMs) when compared with emmetropes(EMMs). These findings have led to speculation that such attenuation may reflect a deficit in inhibitory sympathetic innervation to ciliary smooth muscle in late‐onset myopia and hence a predisposition to sustained accommodative adaptation which then acts as a precursor to the induced myopia. A consequence of this study was that post‐task regression may have some value in predicting those individuals who may be susceptible to post‐task accommodative hysteresis. A pre‐requisite for such a predictive value is that for a given individual the variation in inter‐trial regression patterns is not significant. The aim of this study is principally to Investigate the inter‐trial variability of post‐task regression for individual subjects following a sustained near vision task, and to confirm further differences that have been reported between EMMs and LOMs with respect to the time course of post‐task regressions, A modified Canon Rl infrared optometer was used to measure accommodation objectively throughout a near task and for 2 min post‐task. Accommodative level was measured following 3 min fixation of a high contrast photopic Maltese cross target placed 3 D above the subject's baseline TA. Repeatability of post‐task regression in 10 EMMs and 10 LOMs was assessed by taking measurements on three separate occasions, A significant difference in the post‐task regression patterns between EMMs and LOMs was observed which supports previously reported work; the rate of regression to pre‐task TA being slower in the LOMs. Within‐subject analysis showed that for both EMMs and LOMs the differences between time‐course of post‐task regressions were not significant. The repeatability of post‐task regression patterns thus justifies their use as indices of within‐task adaptation.