Color Vision Deficits and Binocular Vision Dysfunction in Parkinson's Disease

Background/Objectives: Visual dysfunction is a common non-motor symptom in Parkinson's Disease (PD), as evidenced by deficits in color vision (CV) and binocular vision (BV). Computerized CV tests, such as the Cambridge Color Test (CCT), are underutilized in this patient population despite the known limitations of common CV tests. Methods: In total, 19 PD and 12 control participants underwent a comprehensive eye exam, including ocular motility testing and the CCT, utilizing thresholds obtained along 12 contrast vectors to fit a discrimination ellipse. Findings were compared across groups, and the association with disease severity was analyzed. Results: PD participants showed increases in ellipse area (p = 0.012) and short-axis length (p = 0.009). PD participants demonstrated convergence insufficiency type exotropia (p < 0.001) and impaired stereopsis (p = 0.006). No significant correlation with UPDRS scores was seen for either BV or CV. Conclusions: PD participants exhibited binocular vision dysfunction with selective changes in color vision. CV changes are more variable in PD, likely due to mixed parvocellular and cortical dysfunction. Convergence insufficiency type exotropia is more common in PD, likely due to combined cortical and subcortical neurodegeneration. Both BV and CV changes occur independently of motor severity, emphasizing the need for routine visual testing regardless of symptom progression.