Double vision in Parkinson's Disease: a systematic review

Introduction. The prevalence of diplopia in Parkinson's disease (PD) ranges from 10% to 30%. Diplopia is usually limited to specific situations such as reading and looking around, however, it can also be constant. The aim of this review, supplemented by two case studies, was to summarise current knowledge on the frequency, possible causes, differential diagnosis, pathophysiology and treatment approaches to double vision in PD patients. Methodology. An electronic search (PubMed, Scopus, Embase and Web of Science) to identify studies regarding diplopia in PD patients was performed in May 2020. The following search terms were used: Parkinson's Disease and diplopia. Results. Five articles are included in this literature review. In the literature, the number of included patients with PD who presented with symptoms of diplopia varied from a single case report to 88 patients. Diplopia was usually intermittent and binocular. The most commonly reported type of diplopia was single object diplopia, and the second most common was complete diplopia. Risk factors contributing to developing diplopia were: older age, disease duration, disease severity, cognitive decline, presence of visual hallucinations, and higher levodopa equivalent dose. Results also showed that diplopia had a significant impact on quality of life. Possible comorbidities of diplopia include myasthenia gravis and vascular disease. Conclusion. Diplopia is relatively common in PD, but still understudied. The research shows that it has a clear impact on health-related quality of life and patient safety. The acute onset of diplopia should always result in tests to exclude other diseases. Tailored interventions should be developed, leading to improved patient safety, quality of life, and quality of care.