The Dark Side of Light: Spectral Variation in Post-Traumatic Photosensitivity and Its Functional Sequelae

Background/Objectives. Headache and migraine were exacerbated by light during an episode, with light also serving as a diathesis for pain between episodes. Such interictal photosensitivity has been hypothesized to reflect heightened sensitivity to blue-cyan (BC) light, due to activation of melanopsin-based intrinsically photosensitive retinal ganglion cells (ipRGCs). This study examined evidence for wavelength-selective photosensitivity and its relation to headaches/migraine and accompanying functional sequelae. Methods. Individuals with persistent post-traumatic headache (N = 325) were assessed for photosensitivity with an analysis of filtered wavelengths that resulted in relief. A subsample (n = 209) wore precision tinted lenses that matched their individual wavelength photosensitivity profile for over a 1-3-month follow up period and were assessed on a variety of persistent functional complaints. Results. Analysis of wavelengths associated with photosensitivity did not support differential sensitivity to the BC range, revealing greater sensitivity to light below 440 nm and less sensitivity above 680 nm, but with a coefficient of variation of 94.7%, consistent with extremely high individual variation. Individuals who showed near elimination of photosensitivity (97.9%) had decreased self-reported headache frequency (92.6%), as well as reported diminished physical, emotional and cognitive complaints, with these functional outcomes unrelated to the magnitude of BC filtering. Conclusions. These results suggested (1) wavelengths evoking photosensitivity were highly individually variable and (2) interictal exposure to a variety of wavelengths may have contributed to post-traumatic head pain and associated impaired global function, pointing toward common central origins.