Trifocal glasses have been brought into existence for many years to help people aging 40 and over deal with presbyopia, a common condition in the old group. Presbyopia normally causes vision loss in the near range. Traditional reading glasses as a single-vision form of glasses can be simply used to correct presbyopia and enable patients to restore clear, near sight. However, trifocal reading glasses help them restore a fuller range of clear vision. In fact, trifocal eyeglasses are a successor to bifocal reading glasses, which were first created by Franklin in around 1780. Before that time, all people with presbyopia had to carry two pairs of eyeglasses, one for seeing objects in the distance and the other for seeing close up. Thanks to the great U.S. statesman, a single pair of bifocal reading glasses can meet both of these two demands.
In the nineteenth and early twentieth century, inventors made it possible to use round bifocal segments for near vision, which could be fused into the lens containing the distance correction. Present now, there are a wide variety of reading segment designs. A shortcoming of all variations of bifocal reading glasses is that they can not provide intermediate vision aid. As presbyopia advances, vision at the arm’s length will be affected as well. Dealing with this problem, trifocal glasses were developed in the 1940s. These glasses have a second small lens segment placed directly above the near segment. So, a typical trifocal lens has three power zones or focal points. People using trifocal reading glasses can restore clear vision for arm’s length tasks like computer work.
Modern trifocal glasses are slightly different from early ones in design. Currently, most trifocal spectacles have an additional ribbon-shaped lens segment immediately above the near segment. The intermediate segment is for seeing things that are approximately 18 to 24 inches away. Computer monitor, speedometer, and other dashboard gauges are all within the capability of trifocal eyeglasses.
C: Trifocal glasses have an additional lens segment compared with bifocal reading glasses. This added segment is for seeing things being approximately 18 to 24 itches away.
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