If your prescription glasses have two areas in the lenses, then it is most likely you have what is known as bifocals. Some people might call this a double lens.

Firstly, if you have bought these glasses and were not expecting to receive bifocals, then be sure to get in touch with your optometrist to ensure you've been given the correct pair. The purpose of bifocals is twofold. Essentially, they are designed to act as two pairs of prescription glasses in one. When you wear them, you can look straight or slightly up to benefit from clear distance vision. When you drop your eyes downward to read, you will be looking through the short-distance part of the lens, allowing you vision correction for close objects. Bifocals have been around for a long time and are very gradually superseded by the more popular Progressive lenses.