The invention and proper use of bifocal eyeglasses
The invention of convex and concave lenses
The first pair of eyeglasses was invented in the 13th century for people to magnify objects they wanted to see. Using convex lenses, it was used to compromise farsightedness, which was the inability to see items nearby clearly. Later in the 14th century, nearsightedness was also correctable by using concave lenses. This kind of lenses enabled those patients to focus on objects in distance. During the centuries after the invention of concave lenses, people with farsightedness or nearsightedness were able to get normal vision by wearing convex or concave eyeglasses.
The invention of bifocal lenses
However, a third group of patients occurred in the 1700s, exemplified by the invention of bifocal eyeglasses by Benjamin Franklin. This new form of glasses can correct both vision errors for both near and far. Having difficulty in focusing on objects both near and far, Benjamin Franklin had also to travel a lot. During his travels, reading was a regular activity. The problem was that a single pair of concave glasses was not enough and he was forced to swap eyeglasses frequently. Bothered by continuous eyeglass switches, he combined two lenses into one lens. Widely known today, a bifocal lens has a top part for distance vision and a bottom section for viewing close up things.
After several centuries’ development, bifocal eyeglasses are quite popular now. It is estimated that more than half of the individuals who use corrective eyeglasses are bifocal users. They are currently widely used by people who need more than one kind of visual need. Some people may notice that the need for bifocal eyeglasses is increasing as they age. It is true that bifocal glasses are mainly for the old. In most cases, people who wear single vision lenses will switch to bifocal lenses when they enter their 40s. For most new users, it may take some time to get adjusted to a bifocal pair of eyeglasses at the beginning.
Proper use of bifocals
The standard design of a bifocal lens is that the top half is incorporated with a power for distance vision and the bottom half another power for close-up view. Well, this design is significantly different from any kind of single-vision glasses. Myopia or hyperopia glasses have only one focal point, which means that there is only a uniform power across the whole lens. A problem commonly reported by new users of bifocals is that the vision becomes uncomfortable or even headache will be caused. In some cases, peripheral vision especially the vertical vision will be limited because of the power division in the middle of the lenses. Both the near vision section and the distance vision section are narrowed. This is an unavoidable condition for every bifocal user. Furthermore, there are still additional requirements on proper bifocal use. While it is simple to see through myopia or hyperopia lenses and get clear images, bifocal eyeglasses require the user to tilt his or her head slightly up to see objects in the distance and look down mildly to get clear close-up vision. These tips originate directly from the unique lens design described before.
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