The intermediate segment in trifocal lenses is directly above the near seg and is used to view objects at arm's length.Ĭomputers are an excellent example of something that is in a person's intermediate zone. Trifocals have three points of focus - usually for distance, intermediate and near vision. Generally, you look up and through the distance portion of the lens when focusing on points farther away, and you look down and through the bifocal segment of the lens when focusing on reading material or objects within 18 inches of your eyes. The full bottom half of a bifocal lens, called the Franklin, Executive or E style The lens segment (or "seg") devoted to near-vision correction can be one of several shapes:Ī half-moon - also called a flat-top, straight-top or D segmentĪ narrow rectangular area, known as a ribbon segment The rest of the lens usually is for your distance vision. A small portion in the lower part of the lens contains the power required to correct your near vision. Regardless of the reason you need a prescription for near-vision correction, bifocals all work in the same way. In these cases, the bottom portion of the bifocal lens reduces the amount of focusing effort required to see near objects clearly.Īlso, some research suggests wearing bifocals or other multifocal lenses may help control myopia in some children by reducing the focusing demands of reading and near work. Though multifocal lenses usually are prescribed for adults over age 40 to compensate for presbyopia, in some cases bifocals are prescribed for children and young adults who have eye teaming or focusing problems that cause eye strain when reading. Progressive multifocal lenses gradually change in power from the top half of the lens to the bottom, and thus contain many lens powers. Multifocal eyeglass lenses contain two or more lens powers to help you see objects at all distances after you lose the ability to naturally change the focus of your eyes due to age (presbyopia).Įxecutive bifocal lens (also called the Franklin bifocal).īifocals contain two lens powers trifocals have three. In particular, bifocal and trifocal lenses usually provide wider lens areas for reading and computer work than progressive lenses.Īlso, there are many special-purpose bifocal and trifocal lens designs available, including special glasses for computers and for other tasks that require excellent intermediate and near vision. While most presbyopes these days choose line-free progressive lenses, conventional bifocals and trifocals have some advantages over progressives. If you already wear prescription eyeglasses, this generally means you will need to begin wearing multifocal lenses to continue to see clearly at all distances. Some time after age 40, you will begin to notice the symptoms of presbyopia, including that feeling that your arms "aren't long enough" to hold a newspaper or magazine at a position where you can read it clearly.
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