Connections between intrinsically photosensitive retinal ganglion cells and TBI symptoms.

The majority of patients with traumatic brain injury (TBI) are classified as having a mild TBI. Despite being categorized as mild, these individuals report ongoing and complex symptoms, which negatively affect their ability to complete activities of daily living and overall quality of life. Some of the major symptoms include anxiety, depression, sleep problems, headaches, light sensitivity, and difficulty reading. The root cause for these symptoms is under investigation by many in the field. Of interest, several of these symptoms such as headaches, ocular pain, light sensitivity, and sleep disturbances may overlap and share underlying circuitry influenced by the intrinsically photosensitive retinal ganglion cells (ipRGCs). These cells are light sensing, but non-image forming, and they influence corneal function, pupillary constriction, and circadian rhythm. In this review, we discuss these symptoms and propose a role of the ipRGCs as at least one underlying and unifying cause for such symptoms.