Humans view the world through two eyes, but it is our brain that combines the images from each eye to form a single composite picture. If this function becomes damaged, impaired sight can be the result. Such loss of visual function can be observed in patients who have suffered a stroke or traumatic brain injury or when the oxygen supply to the brain has been reduced (cerebral hypoxia). Those affected by this condition experience blurred vision or can start to see double after only a short period of visual effort.