A concussion is a type of brain injury that happens when a blow to the head makes the head move back and forth with a lot of force. More than half of the brain’s pathways are dedicated to vision and eye movement, so a diffuse brain injury such as a concussion will often affect the visual system. Most of the time this happens from damage to the optic nerve, either directly or indirectly. Even a mild concussion can cause problems with vision, such as blurring, sensitivity to light and difficulty focusing on objects. Severe concussions can cause blindness and double vision.