The Screening Visual Complaints questionnaire (SVCq) in people with Parkinson's disease-Confirmatory factor analysis and advice for its use in clinical practice

BackgroundThe Screening Visual Complaints questionnaire (SVCq) is a short questionnaire to screen for visual complaints in people with Parkinson's disease (PD). ObjectiveThe current study aims to investigate the factor structure of the SVCq to increase the usability of this measure in clinical practice and facilitate the interpretation of visual complaints in people with PD. MethodsWe performed a confirmatory factor analysis using the 19 items of the SVCq of 581 people with PD, investigating the fit of three models previously found in a community sample: a one-factor model including all items, and models where items are distributed across either three or five factors. The clinical value of derived subscales was explored by comparing scores with age-matched controls (N = 583), and by investigating relationships to demographic and disease related characteristics. ResultsAll three models showed a good fit in people with PD, with the five-factor model outperforming the three-factor and one-factor model. Five factors were distinguished: 'Diminished visual perception-Function related' (5 items), 'Diminished visual perception-Luminance related' (3 items), 'Diminished visual perception-Task related' (3 items), 'Altered visual perception' (6 items), and 'Ocular discomfort' (2 items). On each subscale, people with PD reported more complaints than controls, even when there was no ophthalmological condition present. Furthermore, subscales were sensitive to relevant clinical characteristics, like age, disease duration, severity, and medication use. ConclusionsThe five-factor model showed a good fit in people with PD and has clinical relevance. Each subscale provides a solid basis for individualized visual care.