Accommodative microfluctuations and pupil diameter

Abstract

The nominally steady-state accommodation response exhibits temporal variations which can be characterized by two dominant regions of activity; a low frequency component (LFC < 0.6 Hz) and a high frequency component (1.0 ⩽ HFC ⩽ 2.1 Hz). There is no consensus as to the relative contribution made by each of the frequency components of the microfluctuations to the control of steady-state accommodation. We investigate the effect of variations in artificial pupil diameter (0.5, 1, 2, 3, 4 and 5 mm pupils) on the microfluctuations of accommodation, while three young emmetropic subjects view, monocularly, a photopic high contrast Maltese cross target placed at a dioptric distance equal to their open-loop accommodation level. Average power spectra were calculated for five accommodation signals, each of 10 sec duration, collected for each viewing condition at a sampling rate of 102.4 Hz using a continuously recording infrared objective optometer. For artificial pupil diameters ⩽2 mm the power of die LFC was found to increase as a function of reducing pupil diameter, while for artificial pupil diameters >2 mm the LFC was found to be relatively constant. No systematic change in the HFC with varying artificial pupil diameter was observed. Changes in the root-mean-square (r.m.s.) value of the fluctuations with varying pupil diameter were significant (one-way ANOVA, F = 8.507, P = 0.0001, d.f. = 89) and showed a similar form to the changes in the LFC. The results support the conclusion of previous computer-derived models of accommodation control systems that control of steady-state accommodation may be mediated through the LFC of accommodative microfluctuations.