Single vision lenses are standard prescriptions for glasses. The glasses have only one viewing area on the entire lens, and the correction area can be used for long distances, medium distances, or reading. For long-distance, if you wear glasses all day but don't have dual/zoom glasses, or need them most of the time to see things far away. For middle distance, if you primarily need this pair of glasses to work on a computer or something else at arm's length or if you are a musician you need this pair of glasses to read music. For reading, if you need to read things around you, such as files, documents, etc.