The authors outlined three hypothesis for the effect Parkinson’s Disease has on blur- and disparity-driven vergence with reference to location within the vergence system that is affected to be tested in this prospective study. The study recruited 14 participants with Parkinson’s Disease and six age-matched controls. Vergence was assessed binocularly and monocularly. Participants with Parkinson’s Disease are reported to have reduced deconjugate response when viewing binocularly and limited disparity-driven convergence compared to the controls. Both the controls and participants with Parkinson’s Disease had limited blur-driven convergence, whereas disparity-drive vergence latency times were reported to be significantly longer for participants with Parkinson’s Disease. Participants with Parkinson’s Disease are reported to use different strategies to achieve vergence compared to the controls. These differences are pictorially represented in the paper. The authors report the findings support that impaired vergence in Parkinson’s Disease is as a result of the disparity controller being affected. The suggestion of where this is anatomically is at the fastigial and interpositus nucleus. This identification of where along the vergence pathway is affected by Parkinson’s Disease, creates an opportunity to identify potential therapy options to treat vergence limitations in Parkinson’s Disease.