Reliability and Validity of Pupillary Response During Dual-Task Balance in Parkinson Disease

Objective To investigate the reliability and validity of pupillary response during dual-task balance conditions in individuals with Parkinson disease (PD). Design Cross-sectional study. Setting University of Kansas Medical Center Parkinson's Disease and Movement Disorder Center. Participants Participants (N=68) included individuals with PD (n=33) and healthy controls (n=35). Interventions Not applicable. Main Outcome Measures Pupillary response was the main outcome measure that was measured during the following conditions: single-task balance eyes open, single-task balance eyes occluded, dual-task eyes open, and dual-task eyes occluded. After each condition, the National Aeronautics and Space Administration-Task Load Index (NASA-TLX) was administered to assess self-reported cognitive workload. To examine the test-retest reliability of the pupillary response, the conditions were administered twice for each individual within 2 hours. Intraclass correlation coefficients (ICC) were used to analyze the test-retest reliability of pupillary response in each condition for both groups. Pearson’s r correlation was used to assess the convergent validity of pupillary response against the NASA-TLX. Results The test-retest reliability was excellent for both groups in almost all conditions (ICC>0.75). There were no correlations between pupillary response and the NASA-TLX. However, increased mental demand (a subitem of the NASA-TLX) significantly correlated with increased pupillary response in individuals with PD (r=0.38; P=.03). Conclusions Pupillary response showed excellent test-retest reliability and validity during dual-task balance for individuals with PD and healthy controls. Overall, these results suggest that pupillary response represents a stable index of cognitive workload during dual-task balance in individuals with PD.