Ambient green light reduces knee pain in osteoarthritis patients

Background: Regular viewing of dim green light has been shown to reduce the pain associated with migraine, fibromyalgia, and post-surgery. Aim: The present study examined whether visual exposure to ambient green light could also alleviate osteoarthritis (OA) pain. Methods: Nineteen patients diagnosed with moderate to severe knee OA pain were exposed to dim white light (6.57 ± 1.00 lux) for 1-2 hours per day for 10 weeks. Following a 2-week wash-out period, patients then received green light treatment (wavelength = 525 nm, 6.82 ± 0.78 lux) for 1-2 hours per day for a further 10 weeks. The primary outcome measure was changes in arthritis disability score as measured by the Western Ontario and McMaster University Arthritis Index (WOMAC) questionnaire. Secondary outcomes included patient-reported changes in pain intensity, pain disability, and patient global satisfaction. Results: With green light therapy (GLT), average WOMAC scores decreased from 44.1 ± 17.5 at baseline to 32.5 ± 16.2 whereas white light therapy (WLT) had no significant effect on arthritis disability scores (39.6 ± 15.3). While both WLT and GLT reduced pain intensity, the analgesic effect of green light was significantly greater. Pain interference scores were lower following GLT whereas WLT had no effect on this parameter. The Patient's Global Impression of Change was significantly improved over baseline with both WLT and GLT. Conclusion: Daily exposure to ambient green light had a beneficial effect on OA knee pain. The neural pathways between the visual system and central pain modulation regions requires further investigation.