Absence of adaptive plasticity after voluntary vergence and accommodation

Subjects maintained their eyes crossed (verged) for a period of 8 min in darkness with monitoring provided by an infrared video system. Changes in resting vergence (RV) and resting focus (RF) were examined. Results showed: (i) visual stimulation was not necessary for adaptation of either RV or RF, but (ii) these purely motor effects were significantly smaller and more dissipative than those attributable to visually driven adaptation, and (iii) voluntary vergence amplitude was negatively correlated with pupil size. Assuming that voluntary vergence is driven by accommodation, then the voluntary signal must enter the oculomotor control system prior to the cross links between channels, but beyond the site of the visually driven adaptive elements.