A month of daily bright light therapy significantly improved visual function and alleviated clinical symptoms in patients with Parkinson’s disease (PD), according to a study published in BMC Psychiatry. Participants also reported reduced daytime sleepiness, anxiety, and other non-motor symptoms.
“Recent studies examining the retina in PD patients using optical coherence tomography, pattern electroretinogram, and visual evoked potentials have found significant abnormalities, including delayed latencies and reduced wave amplitude,” wrote Wei-ye Xie of the Second Affiliated Hospital of Soochow University, China, and colleagues. “Exploring whether retina-focused assessments can serve as therapeutic biomarkers in PD remains a promising avenue.”
Study Design and Findings
Xie and colleagues conducted a crossover, randomized, placebo-controlled trial with 23 PD patients. Participants underwent 30 days of either bright light therapy or dim light therapy, followed by a 30-day washout period, then switched treatments.
Both therapies were administered daily for one hour in the morning and one hour in the afternoon. Bright light therapy was delivered at 10,000 lux, while the dim light control was 200 lux, both at a 45° angle from the patient’s line of sight.
Results showed significant improvement in bilateral N95 latencies on pattern electroretinogram (P < .01) and P100 latencies on visual evoked potentials (P < .01). Retinal nerve fiber layer thickness remained unchanged.
Bright light therapy also reduced clinical symptoms: participants showed improvement on the Epworth Sleepiness Scale (P = .025), 14-item Hamilton Anxiety Scale (P = .04), Parkinson’s Disease Questionnaire-39 (P = .035), and Autonomic Scale for Outcomes in Parkinson’s Disease (P = .02).
“This study is the first to demonstrate the safety and efficacy of bright light therapy in PD patients using ophthalmological assessments,” the researchers noted. They suggested that improvements in visual pathways, rather than retinal structural changes, may underlie the therapy’s benefits.
Expert Perspective
Joann Cherian, OD, FAAO, highlighted the potential clinical impact: “Bright light therapy in PD improves visual pathways, which may help reduce daytime sleepiness, anxiety, and improve quality of life. However, maintaining one hour in the morning and evening at a 45° gaze angle for a month could challenge patient compliance. Accessible home devices would be key.”
Cherian noted study limitations, including the small sample size of 23 and exclusion of patients with prior ocular surgery. She emphasized the need for larger, long-term studies to evaluate maintenance therapy and potential structural retinal improvements, suggesting follow-ups at one and five years could provide deeper insight.
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