The first and the simplest is the single vision lens. This lens allows for one prescription whether it’s set for distance vision, near vision or anywhere in between. In the case of reading glasses, the focal length of the lens is dependent on the prescription of the lens, hence you may be prescribed a different strength for certain tasks. Someone who works on small details at a close distance such as painting nails will need a stronger prescription compared to someone who works on a large computer screen at arm’s length away.
Following on from single vision lens came the need for a lens that enabled someone to see far and near in the circumstances where two different prescriptions were needed. From this, bifocal lenses were created where the second/near lens is added to the bottom area of the lenses. The prescriptions are basically stuck together and rely on your eyes to move down when wanting to see through the stronger area of the lens. There is a marked line that separates the two prescriptions.
Multifocal, also known as graduated and progressive lenses, were later created to help with the sudden jump that bifocals give when looking through the two sections. Multifocals slowly transition from one prescription at the top of the lens to a different prescription lower down. This gives a more natural viewing experience when looking through lenses and no line in your vision. These lenses are technically more complex to create and require accurate measurements, however, people often don’t go back to other options after they’ve experienced the convenience of these lenses.
As well as these options, there are also additions you can add to any of your lenses. The most common are transitions or photochromatic lenses and anti-reflection coatings.
Transitions or photochromatic lenses are where UV light causes the lenses to darken which essentially lets your glasses act as sunglasses. So, for example, you may have single vision distance glasses which are clear with transitions so that they go darker in the sun as well.
Anti-reflection coating is a multi-layer coating that reduces reflections off the lenses and can be applied to lenses during manufacturing. It also means the lenses are clearer to look through and makes it easier for people to see your eyes without all the annoying reflections. Some coatings also provide UV protection, a hard coat to reduce scratches and water and oil repelling technology. The coating is applied to the front and back of the lenses.