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Randomized Controlled Trial
. 2025 May 12;25(1):476.
doi: 10.1186/s12888-025-06915-z.

Bright light therapy in Parkinson's disease: a pilot study on visual pathway improvements

Wei-Ye Xie #  1 , Hui Lou #  2 , Jia-Ying Liu  3 , Jie-Yun Yin  4 , Tian-Qi Zhang  2 , Cheng-Jie Mao  1 , Fen Wang  3 , Chun-Feng Liu  5   6 , Yun Shen  7
Affiliations
Randomized Controlled Trial

Bright light therapy in Parkinson's disease: a pilot study on visual pathway improvements

Wei-Ye Xie et al. BMC Psychiatry. .

Abstract

Background: Bright light therapy (BLT) has been proved to have beneficial effects on Parkinson's disease (PD), the mechanisms remained unclear. Improvements of visual pathways might be key to BLT.

Objective: The aim of this study is to validate whether BLT improves clinical symptoms in PD and explore the possible mechanisms of visual pathways evaluated by optical coherence tomography (OCT), pattern electroretinogram (PERG) and visual evoked potentials (VEP).

Methods: Twenty-three PD patients were enrolled in this crossover randomized placebo-controlled study. Participants received either one month of BLT or dim light therapy (DLT), separated by one-month wash-out period, followed by another intervention. Participants underwent clinical scales, and visual-related evaluations including OCT, PERG and VEP before and after each intervention. Mixed-effects regression models were used to determine the effect between BLT and DLT on improving the differentials of clinical scales (Δscales), OCT (Δretinal thickness), PERG (ΔPERG values) and VEP (ΔP100 latencies). Correlations between clinical symptoms and visual evaluations improvements were analyzed in PD patients receiving BLT.

Results: Excessive daytime sleepiness, anxiety, life quality and autonomic function were improved after BLT. Compared with DLT, bilateral ΔN95 latencies for PERG and ΔP100 latencies for VEP were improved after BLT. We did not observe the changes of four quadrants retinal nerve fiber layer (RNFL) thickness after BLT or DLT.

Conclusions: BLT is a valuable and safe non-pharmacological intervention for improving visual function in PD patients.

Significance: These findings extend neural mechanisms of BLT to visual pathways improvements.

Keywords: Bright light therapy; Optical coherence tomography; Parkinson’s disease; Pattern electroretinogram; Randomized crossover controlled trial; Visual evoked potentials.

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Conflict of interest statement

Declarations. Ethics approval and consent to participate: Statement that all methods are performed in accordance with relevant guidelines and requlations. This study received approval from the Ethics Committee of The Second Affiliated Hospital of Soochow University, China (JD-LK-2020-062-01). Having explained the nature of the survey, confirming that informed consent was obtained from all subjects and/or their legal guardian(s). Each participant’s privacy was safeguarded with respect to the processing of personal data and the confidentiality of individual records and accounts was ensured. Consent for publication: Not Applicable. Competing interests: The authors declare no competing interests. Conflict of interest: None declared. Disclosure statement: There are no financial or non-financial disclosures related to this article.

Figures

Fig. 1
Fig. 1
Study flow diagram. A total of 29 participants were screened, 6 were excluded following screening, 23 consented and started baseline and were randomly assigned. A total of 23 completed the first period, 21 completed both periods (2 participants discontinued due to being conflict with daily working hours). Abbreviations: COVID-19 = coronavirus disease 2019, Order 1 = intervention order starting with BLT first, Order 2 = intervention order starting with DLT first, BLT = bright light therapy, DLT = dim light therapy
See this image and copyright information in PMC

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