Cybersickness Evaluation in Immersive Virtual Environments: A Systematic Review with Implications for Neurological Rehabilitation

<b>Introduction.</b> The proliferation of immersive virtual reality (VR) technologies has transformed the way individuals interact with digital environments, offering unprecedented opportunities in fields ranging from entertainment and education to healthcare and mental health interventions. Immersive VR is increasingly being implemented in motor and cognitive programs in neurorehabilitation, where patient safety and treatment adherence are critical. Despite its relevance, the conceptualization and measurement of cybersickness (CS) remain fragmented across disciplines, with various assessment tools developed in isolation, targeting different symptom domains, populations, and use contexts. <b>Aim.</b> The aim of this systematic review is to identify, categorize, and critically appraise all existing instruments and scales developed to measure CS associated with immersive VR use. The secondary objectives involve examining the psychometric properties of the identified instruments to provide robust evidence for clinicians in assessing CS associated with VR, thereby supporting future scale development and standardization. Additionally, a further objective is to evaluate the specific applicability of these instruments and scales for measuring CS within neurorehabilitation settings, given the growing use of immersive VR in clinical practice with neurological populations. <b>Methods.</b> This systematic review was conducted in accordance with the Guideline for reporting systematic reviews of outcome measurement instruments (PRISMACOSMIN). The review protocol was prospectively registered in the International Prospective Register of Systematic Reviews (PROSPERO). Data extraction was performed independently by the two reviewers, and discrepancies were resolved by consensus or consultation with a third reviewer. To assess the psychometric robustness of existing CS assessment instruments used in virtual reality settings, we applied the methodology proposed by the COSMIN (COnsensus-based Standards for the selection of health Measurement INstruments) initiative for systematic reviews of patient-reported outcome measures (PROMs). The evaluation was structured across three steps: Assessment of risk of bias; Quality of measurement properties and Summary of evidence; and Grading of Recommendations Assessment, Development and Evaluation (GRADE) guidelines. <b>Results.</b> Nine assessment instruments were included in this review. Following our analysis, the CSQ-VR and VRNQ received a Grade A recommendation, as they met sufficient criteria for both internal consistency and structural validity with high methodological quality. Few instruments have reported validations in specific clinical populations related to neurorehabilitation, including individuals with neurological conditions such as brain injury, multiple sclerosis (MS), migraine-associated vestibulopathy, vestibular disorders or cognitive impairment, indicating a critical gap in scale generalizability across clinical contexts. <b>Conclusions.</b> Despite the increasing use of immersive VR, few CS assessment tools have been designed and validated, reaching the CSQ-VR and VRNQ a Grade A recommendation. Among the nine identified assessment instruments, only the SSQ, MSAQ, CSQ-VR, VRNQ MSSQ and SEQ have been employed in samples with neurological disorders. There is a critical need for standardized CS VR-specific tools with robust psychometric properties to ensure safe and effective implementation in neurorehabilitation settings.