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.

Progressive lenses provide a smooth transition from the distance through intermediate to near, with all the in-between corrections included as well. You can look up to see anything in the distance, look ahead to view your computer in the intermediate zone, and drop your gaze downward to read, and do fine work comfortably in the close site. That is to say, progressive lenses are the closest to how natural vision is that you can get in a pair of prescription eyeglasses.