Single vision lenses function as all-purpose glasses for persons who have normal accommodation. Persons who normally wear bifocals or trifocals can use single vision for distance or near lenses (Readers). They can also function as occupational glasses for certain types of work. Single vision lenses are available in all lens materials
These lenses provide special visual and cosmetic benefits for stronger corrections and increase edge to edge clarity. Flatter than conventional lenses, aspherics eliminate the "bulgy" appearance of strong plus lenses and greatly enhance the appearance of finished eyewear. Persons with strong nearsighted corrections also benefit from thinner, lighter weight glasses when their lenses are aspheric. Because aspheric lenses are positioned closer to the face, there is less eye magnification with farsighted corrections and less of the "small eyes" look with nearsighted corrections. Aspheric lenses are often made of high index materials for the ultimate in thin lenses.
This is the most popular bifocal format and is available with the bifocal portion made in a variety of widths to help with various close-up occupations. Flat-top bifocals are made in every type of lens material.
Trifocals come in a variety of designs. Flat-top trifocals are the most widely used form. The added segment provides clear vision at arm's length distance, the area that is usually blurred for bifocal wearers. Trifocals are available in all lens materials.
Progressives (No-line Bifocals):
These lenses provide all the benefits of bifocals but add the feature of continuous clear vision at all distances, including mid-range distance (arm's length). Progressives have the cosmetic advantage of appearing to be single vision lenses so they never reveal that the wearer is using bifocals. They are available in all lens materials and also made in aspheric form. Because of their many benefits, they are becoming the lens of choice for bifocal and trifocal wearers. A progressive lens designed for all-round use has three zones of vision: the distance, mid, and near zones. The transitions between these zones are smooth and invisible.