Fatigue of accommodation and vergence modifies their mutual interactions.

Aftereffects of accommodation and convergence demonstrate the adaptability of these two visual motor systems. These aftereffects were reduced after ramp tracking exercises of either accommodation or vergence, and this reduced aftereffect or fatigue was associated with an increase of accommodative vergence and vergence accommodation. When one motor system (accommodation or vergence) adapted more readily than the other, fatigue caused an increase of the cross-link interaction originating from the more adaptable motor system and a reduction of the cross-link interaction originating from the less adaptable motor system. These results suggest an inverse relationship between adaptation and the cross-link interactions between accommodation and vergence and that adaptation of tonic accommodation and tonic vergence is a process that underlies plasticity of accommodative vergence and vergence accommodation respectively.