Accommodative hysteresis: a precursor for induced myopia?

After an 8-min fixation period, the dark focus of accommodation of 12 emmetropes either increased by -0.34 diopters (D) or relaxed by 0.21D depending upon whether the fixation target was at the near point or far point, respectively. No significant shifts occurred after fixation at the distance of the subject's dark focus. The obtained shifts had long time-constants as measured after 16 min in darkness. Decay was much slower after near point (tau = 123.1 min) rather than far point (tau = 14.4 min) fixation.