Mean response and oscillations of accommodation for various stimulus vergences in relation to accommodation feedback...

Mean responses and fluctuations of accommodation were recorded by means of a high-sensitivity infra-red optometer over a large dioptric range (+3 to -9 D). We found that both the effective absolute amplitude and the 2 Hz relative activity of fluctuations of accommodation exhibit a maximum within the -1 to -4 D range of stimulus vergence for which the focus error (lag of accommodation) is minimal, whereas no activity is observed at the subject's near and far points. But the 2 Hz relative activity of accommodative fluctuations provides a better description of the control; this parameter was found to be positively correlated with the sensitivity of the accommodative system to defocus blur (input of the feedback loop), providing support for the active role of these fluctuations in the accommodative system.