When you enter a glasses shop and try to buy a pair of glasses, you have several types of lens options depending on your prescription. But many people get confused by the terms single vision, bifocal and progressive. These terms refer to how the lenses in your glasses are designed. But if you are not sure about what type of glasses your prescription requires, here is a quick overview to help you get started.
1. What Are Single Vision Lenses?
A single vision lens is essentially a lens that holds one prescription. This type of lens is used for prescriptions for people who are nearsighted, farsighted, have astigmatism, or have a combination of refractive errors. In many cases, single vision glasses are used by people who need the same amount of power to see far away and close up. However, there are single vision glasses prescribed for a specific purpose. For example, a pair of reading glasses that are used only for reading contains a single vision lens.
The single vision lens is ideal for most children and younger adults because they typically don’t need to adjust their vision correction based on their distance. Your single vision glasses prescription always includes a spherical component as the first number on your prescription and may also include a cylinder component to correct for astigmatism.
2. What Are Bifocal Lenses?
Bifocal lenses have two separate areas of vision correction. The areas are divided by a distinct line that sits horizontally across the lens. The top part of the lens is used for distance, while the bottom part is used for near vision. The part of the lens that is devoted to near vision can be shaped in a couple different ways: D segment, round segment (visible/invisible), curve segment and E-line.
Bifocal lenses are usually used if someone is the rare person who cannot adapt to progressive lenses or in young children whose eyes cross when they read. The reason they are becoming less utilized is that there is a common problem caused by bifocal lenses called “image jump”, in which images seem to jump as your eyes move between the two parts of the lens.
3. What Are Progressive Lenses?
The design of progressive lenses is newer and more advanced than bifocals. These lenses provide a progressive gradient of power from the top of the lens to the bottom, offering seamless transitions for different vision needs. Progressive eyeglass lenses are also called a no-line bifocal because they have no visible line between the segments, which makes them more aesthetically pleasing.
Moreover, progressive eyeglasses also create a smooth transition between the distance, intermediate, and near portions of your prescription. The intermediate portion of the lens is ideal for mid-range activities such as computer work. Progressive eyeglasses have the option of a long or short corridor design. The corridor is essentially the part of the lens that gives you the ability to see intermediate distances.
In a word, single vision (SV), bifocal, and progressive lenses each offer distinct vision correction solutions. Single vision lenses correct for a single distance (near or far), while bifocal and progressive lenses address both near and far vision in a single lens. Bifocals have a visible line separating the near and distance portions, whereas progressive lenses offer a seamless, graduated transition between distances without a visible line. If you need any more information, please feel free to contact us.