Case Report: Green Light Exposure Relieves Chronic Headache Pain in a Colorblind Patient.

Patients with chronic headaches sometimes prefer non-pharmacological methods for pain management. We have shown previously that green light exposure (GLED, Green Light Emitting Diode) reversed thermal hyperalgesia and mechanical allodynia in a rat model of neuropathic pain. This effect is mediated through the visual system. Moreover, we recently showed that GLED was effective in decreasing the severity of headache pain and the number of headache-days per month in migraine patients. The visual system is comprised of image-forming and non-image-forming pathways; however, the contribution of different photosensitive cells to the effect of GLED is not yet known. Here, we report a 66-year-old man with headaches attributed to other disorders of homeostasis and color blindness who was recruited in the GLED study. The subject, diagnosed with protanomaly, cannot differentiate green, yellow, orange, and red colors. After completing the GLED exposure protocol, the subject noted significant decreases in headache pain intensity without reduction in the number of headache-days per month. The subject also reported improvement in the quality of his sleep. These findings suggest that green light therapy mediates the decrease of the headache pain intensity through non-image-forming intrinsically photosensitive retinal ganglion cells. However, the subject did not report a change in the frequency of his headaches, suggesting the involvement of cones in reduction of headache frequency by GLED. This is the first case reported of a colorblind man with chronic headache using GLED to manage his headache pain and may increase our understanding of the contribution of different photosensitive cells in mediating the pain-relieving effects of GLED.