Difference Between Single Vision and Bifocal Lenses
Typical eyeglasses are generally categorized into four different categories. These include single vision eyeglasses, bifocals, trifocals and multi-focal lenses. Although both are common, single and bifocal lenses have a number of differences.
Single Vision Lenses
These lenses refer to eyeglasses containing the exact same power, or focal power, distributed throughout the entire lens. The focal power is the same on the top of the lens and at the bottom of the lens. In addition, these lenses can be used in the treatment of astigmatism, farsightedness, nearsightedness, and combinations of these condition. Typically, people that wear corrective lenses under 40 years of age wear this type of corrective lens.
Bifocal lenses are comprised of two parts. The top, or upper most part of the lens is typically used by people needing help with distance vision. The lower portion of the lens is normally used for those needing help for reading and other near-vision activities. Presbyopia, a deficit in the lens’s ability to contract and expand, is a condition common in people over age 45. People with presbyopia usually wear bifocal lenses to correct their visual deficits. Bifocal eyeglasses used to have a telltale line separating the top and bottom of the lens, however, eyeglasses can now be made so that the changes in lens power are undetectable.