Researchers found that the five-factor questionnaire used in this study seemed to be a more accurate method of screening for Parkinson’s disease in elder patients.  Photo: Shutterstock.

Optometrists are increasingly attuned to the ways in which central nervous system disorders like Alzheimer’s disease and Parkinson’s disease (PD) affect ocular and visual status. A new study evaluated the methods of screening PD patient symptoms. Patients typically use the Screening Visual Complaints (SVC) questionnaire, and new research indicates this model may be better suited in a way that the items of the questionnaire are distributed across five differing factors. The form itself can be downloaded for use in practice here.

The study included comparisons between three scales: a one-factor model including all 19 items used, a model where items are distributed across three factors and a final model where items are distributed across five factors. While all three models distinguished a good fit for people with Parkinson’s, the five-factor model outperformed both other models, and the three-factor outperformed the one-factor. The five factors that were included were: 

  • diminished visual perception—function-related
  • diminished visual perception—luminance-related
  • diminished visual perception—task-related
  • altered visual perception
  • ocular discomfort

Out of the 581 people with PD observed, with each of the five subscales, they reported more complaints than control subjects. This included even when there were no ophthalmological conditions present. Additionally, the subscales displayed sensitivity to the factors of age, disease duration, severity, and amount of medication usage. Subsequently, the researchers pose that visual complaints likely increase with progression of the disease. 

Each of the three models displayed a reasonable fit in a community sample as well as in those with PD. This means that each model corresponds to the same construct underlying what factor an item was placed under. While any of the models could be justified in their usage, since they all correspond to the same measures, the fact that both the three- and five-factor models both outperformed the one factor indicates that it indeed may be more valuable to separate the 19 total items into three or five subscale scores. Doing so would generate different subscores for each category of the SVC rather than a composite, total SVC score that does not indicate more specifically the type of vision problems experienced. 

An example illustrating the benefit of the five included factors may include if people experience complaints related to luminance, such as sensitivity to light because of cataract or other ocular media opacities. Solutions can be easier addressed, since this type of complaint falls under the luminance-related factor, making it easier to identify the type of action needed to be taken to provide a solution.

The authors conclude that the five-factor SVC model most likely provides a better basis for helping patients than the other two models. For practicing clinicians who would encounter these patients, they posit “regular screening for visual complaints in people with PD is advised, even if no known ophthalmological condition is present. Regular screening results in early detection of visual complaints, which may subsequently lead to more optimal care and rehabilitation, preventing further worsening of visual complaints and associated poor outcomes, such as anxiety, depression and dementia.”

van der Lijn I, de Haan GA, van der Feen F, et al. The Screening Visual Complaints questionnaire (SVCq) in people with Parkinson’s disease—confirmatory factor analysis and advice for its use in clinical practice. PLoS ONE. September 14, 2022. [Epub a head of print].