Unanswered questions in headache: so what is photophobia, anyway?

Photophobia refers to a sensory disturbance provoked by light. However, because it arises distinctly in a broad range of clinical conditions, its definition remains elusive. Many underscore the painful sensory aspects of photophobia, while others emphasize its unpleasant, affective qualities. To add further complexity, recent discoveries in photophobia research have raised disparate and potentially conflicting results. In this installment of an occasional series, we asked clinicians and scientists to give their interpretation of what these discoveries tell us about photophobia in the clinic, and vice versa.