 The pupils inside the eyes constrict in response to light stimulation. Different classes of cells within the human retina initiate this response. Recent research suggests that one of the ganglion cell types involved in this pupil response also plays a role in the photophobia experienced by migraine sufferers. The main aim of this study is to determine whether this type of ganglion cell becomes hypersensitive after traumatic brain injury, thereby contributing to symptoms of increased photosensitivity experienced by many of these individuals. 