What causes photophobia?

Photophobia, or the aversion to light, can be caused by various neurological pathways related to how we perceive and react to light. One cause is related to the inflammation response in the body, particularly when someone is ill. This triggers a specific pathway involving the vagus nerve which sends signals to the thalamus and then the meninges surrounding the brain, resulting in photophobia and sometimes headaches. This response encourages the individual to seek a dark, quiet place to rest (1).

Another contributing factor is the activation of intrinsically photosensitive retinal ganglion cells in the eyes by certain wavelengths of light (especially bright blue and green). These cells are connected to neurons that process sensory information concerning pain at the level of the meninges. Thus, the exposure to bright lights can trigger or amplify feelings of photophobia due to the generation of pain at the level of the meninges (2).

Overall, the body's response to light during inflammation or pain processing illustrates a complex sensory interaction that leads to photophobia.