1. Congenitally Blind: have been totally blind from birth.
2. Adventitiously Blind: lost their vision, but after they had already established important visual memories and concepts.
3. Functionally Blind: have little useful vision.
4. Low Vision: significantly visually impaired, but may be able to use some vision quite efficiently.
5. Legally Blind: central visual acuity of 20/200 or less in the bettr eye after best correction with glasses
