People with a neurodegenerative disorder, such as Parkinson’s disease, dementia and multiple sclerosis (MS) frequently deal with visual problems [1,2,3]. However, since these problems may not be easy to describe and since symptoms that are more eminent, visible, or acute may receive greater emphasis, visual problems and their impact on daily life’s challenges may remain unattended to in clinical settings [4, 5].
A recent study by this author [6] found that the prevalence of visual complaints among people with MS (pwMS) is higher than previously estimated. Up to 90% of pwMS reported to experience some kind of visual complaints in daily life. Complaints regarding light, such as a difficulty adapting to lighter or darker environments, being blinded by bright light or needing more light were especially common, next to for example the feeling to need more time to see something, changes in the visual field, or problems with depth perception. Overall, the nature of the complaints showed a large variability. Furthermore, the study revealed that pwMS with and without a history of optical neuritis (ON) reported similar complaints and the complaints could occur anytime along the disease course.
The study by van der Feen [6] made use of the Screening Visual Complaints questionnaire (SVCq; [7], see Appendix 1 and 2), a questionnaire that has been developed to quickly screen for the presence and nature of visual complaints in people with Parkinson’s disease, dementia and MS. The SVCq assesses subjective visual complaints on a functional level, while previously used questionnaires primarily assess vision related quality of life in daily activities, such as the NEI-VFQ, the NEI-VFQ-25 or MSVQ-7 [8,9,10]. The SVCq is comprised of 19 items reflecting visual complaints, which could be rated on frequency of occurrence. The SVCq may help direct attention to visual complaints and may support in referring people with visual complaints to fitting care or rehabilitation.
In a normal Dutch sample (people without MS or other severe neurological, ophthalmological or psychiatric disorders), the SVCq showed satisfactory validity, good internal consistency (α = 0.85), and good test–retest reliability (ICC = 0.82; [7]). In addition, Huizinga [7] performed a factor analysis and proposed a three-factor model of the 19 items, including the factors diminished visual perception, altered visual perception, and ocular discomfort. Along with the proposed three-factor structure, Huizinga [7] found an acceptable fit for the one-factor model (all 19 items comprised in one factor) and a five-factor model, where the diminished visual perception factor from the three-factor model was divided into three separate factors, being function related, luminance related and task related (see Fig. 1 for a summary of the models and their corresponding items).
These promising factor models should however also be investigated in clinical samples, since the SCVq was specifically developed for people with Parkinson’s disease, dementia and MS. Van der Lijn et al. (submitted) investigated the fit of the three models in a representative sample of people with Parkinson’s disease and was able to confirm good fit of all three models.
In order to be able to make optimal use of the SVCq in clinical care for pwMS, we aim to assess the factor structures of Huizinga [7] in a clinical sample of pwMS, using confirmatory factor analysis (CFA).