Background: Several types of visual illusions can occur in Parkinson's disease (PD). However, the prevalence and types of specific illusions experienced by patients with PD remain unclear. This study aimed to investigate the types of illusions.
Methods: A questionnaire of visual illusions was developed through a literature review in consultation with clinicians and neurologists. Based on the questionnaire, 40 consecutive patients with PD were asked a series of Yes/No questions regarding 20 types of visual illusions since the onset of PD. If participants answered 'Yes', they were then asked to detail their experience(s).
Results: In total, 30 patients with PD had experienced visual illusions since disease onset; among them, 25 were still experiencing them at the time of the study. The most commonly observed illusion types were dysmorphopsia, complex visual illusions, metachromatopsia, and diplopia. Other observed illusions included textural illusions, macropsia, micropsia, teleopsia, pelopsia, kinetopsia, akinetopsia, Zeitraffer/Zeitlupen phenomena, tilt illusion, upside-down illusion, and palinopsia. Additionally, aberrant perception of surface orientation (inclination) was reported, which is yet to be reported in association with any disease. Visual illusions had detrimental effects on the patients' daily lives in some cases.
Conclusions: Systematic interviews regarding the incidence and details of visual illusions experienced by patients with PD could offer important information regarding their quality of life.
Keywords: Parkinson's disease; optical illusions; vision disorders; visual perception.
© 2021 The Authors. Psychogeriatrics published by John Wiley & Sons Australia, Ltd on behalf of Japanese Psychogeriatric Society.