Temporal variations in accommodation during steady-state conditions.

The amplitude of the naturally occurring 2-Hz lens fluctuations at levels of accommodative response ranging from 1 to 4 D were measured in absolute terms (i.e., in diopters) and compared with the overall variability of accommodation (in the time domain) over the same range of accommodative output levels. The amplitude of the 2-Hz component was found to be positively correlated with the mean level of the accommodative response. It was as small as 0.02 D (mean to peak) when the mean response level was 1 D, and it was no larger than 0.1 D (mean to peak) when the mean response level was 4 D. Furthermore, the overall variability of accommodation (in the time domain) was also found to be positively correlated with the mean response level, having its minimum when the accommodative response level was least rather than at the resting focus of accommodation (when neurologic activity is least). This suggests that the observed increase in accommodative noise with dc (response) level is more likely attributed to plant noise than to neurologic (controller) noise.