The effects of the accommodative stimulus and age on the accommodative microfluctuations were investigated in human subjects. Accommodative responses were measured by using an infrared (IR) optometer, and accommodative microfluctuations were quantified by power spectrum analysis. Two frequency bands were determined: low frequency components (< 5 Hz, LFC) and high frequency components (1.3 to 2.2 Hz, HFC). Among younger subjects, the changes in the HFC in response to the accommodative stimuli differed between subjects. The activity of the HFC reached a peak in the center of the accommodation range, whereas the activity of the LFC was its maximum in the presence of darkness or blur in the over-accommodation range. Smaller changes in the magnitude of the HFC were observed in older subjects. Although the LFC may be controlled neurologically, the HFC seems to arise from mechanical and elastic properties of the lens, and may be modulated by other physiological rhythmic variations.