Transfer of fixation between targets at different viewing distances involves changes in vergence eye movements and accommodation that operate to eliminate disparity and blur, respectively. During pinhole viewing, when blur cues are absent, changes in vergence due to disparity result in linear changes in accommodation: the vergence-accommodation response. Experiments were undertaken to determine whether these open-loop responses are subject to visually-mediated adaptive regulation. Human subjects were fitted with specially made laterally-displacing periscopic spectacles to increase the apparent separation of their two eyes and thereby decrease the required change in accommodation per unit change in vergence to maintain single, clear vision. Thirty minutes of exposure to these spectacles was sufficient to cause large decreases in the accommodative change associated with a unit change in vergence during pinhole viewing. This demonstrates that the coupling between vergence and accommodation is subject to adaptive regulation. Decreasing the apparent separation of the eyes with medially-displacing (cyclopean) spectacles failed to affect the magnitude of the vergence-accommodation response. Thus, the adaptive mechanism shows considerable asymmetry.