Effects of Parkinson Disease on Blur-Driven and Disparity-Driven Vergence Eye Movements

Synchronous movements of the 2 eyes in the opposite direction, disconjugate movements such as ver- gence, facilitate depth perception. The vergence eye move- ments are affected in Parkinson disease (PD). Visual blur (accommodation) and fusion (retinal disparity) are important triggers for the vergence. The neural circuit responsible for blur-driven and disparity-driven vergence is tightly coupled. We investigated the effect of PD on these 2 vergence paradigms. In the experiment involving 14 patients with PD and 6 healthy controls, substantial differences between blur- driven and disparity-driven vergence were found. The gain (ratio of actual vs desired eye movements) was reduced in patients with PD in case of disparity-driven vergence but not in blur-driven vergence. The latency of disparity-driven ver- gence onset was significantly longer for patients with PD compared with healthy controls.