There are different levels or variations of blindness that measure how serious the condition can be. To be totally blind means zero perception of light and form. There are blind individuals who can discern dark from light but see nothing else. There are also individuals who have a very limited amount of sight but are considered legally blind. There are a variety of blindness causes that may be to blame for vision loss. For some blindness is a condition that exists since birth, for others it is a condition that occurs during childhood or adulthood as the result of a disease, disorder or injury.