What Is Bifocal Lens?
Changes in vision seem to be related to age. Presbyopia, a common eye condition that occurs in middle age, causes changes in your eye’s ability to focus. But this condition can be corrected by wearing bifocal glasses.
Bifocal lenses are divided into two parts to accommodate two different prescriptions in one lens. One area of the lens will have one prescription (usually distance) and a segment in the lower half will have the other (usually near vision).
The bifocal glasses were invented by Benjamin Franklin, who solved his own vision problem by taking the lens from his reading glasses and distance glasses and cutting them in half. Then remade the cut lenses into a single pair of bifocals and put the distance lens on top and the reading lens on the bottom.
What are bifocals?
A bifocal lens is a lens with two focal points. Because of the imaging principle of the lens, even half of the lens can still present a complete image, and the two images do not interfere with each other. In the past, both short-sighted glasses and presbyopia glasses were called single-focal lenses, which had only one focus. Later it developed to the bifocal lens, and the same lens is divided into upper and lower two parts. The upper part of that lens is used when seeing far, and you look down when seeing close objects, just the reading distance, naturally used the second half.
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How many degrees of myopia do I need to wear glasses?
Students are the most nearsighted because they need to read and study every day. Many people have myopia during their student days. During the physical examination, everyone will check their eyesight first. Generally speaking, if the visual acuity is lower than 0.6, it means that you may be near-sighted to 0 degrees. At this time, you need to go for optometry to see the specific vision situation and see if you need to wear glasses. If the visual acuity tested exceeds 200 degrees, you must wear glasses at this time. If you do not wear glasses, your vision will be greatly affected, and the degree of myopia will rise quickly. For this reason, you must wear glasses in time to correct your vision. If the degree of myopia does not exceed 0 degrees, this is pseudo-myopia and does not require glasses. However, you should always take care to protect your eyes, avoid staring at things at close range for a long time, and don't let your eyes get too tired, so your vision will slowly return to normal.
What Are Varifocal Glasses?
Varifocal glasses, also known as varifocals, varifocal lenses, PALs, or progressive lenses, have a gradual change in strength from the top of the lens to the bottom with multiple focal points in between. This allows you to see all distances and focus points through just one lens. Varifocal lenses are typically used when you have two prescriptions, one for distance and one for reading.
There are three regions of a varifocal lens which are distant zone, intermediate zone and, near/reading zone. Usually, the upper portion of the varifocal lens is the distant zone and the bottom portion of the varifocal lens is the near or reading zone.
One of the benefits of varifocal glasses is that you do not need to prepare 2 separate pairs of glasses or need to switch between frames for different vision needs.
Can lens thickness affect eyeglasses definition?
The lens thickness of myopic glasses will not affect definition, so you can choose the glasses with appropriate degrees according to your own situation. It is recommended to choose the lens with a membrane, which can increase the transmittance and can play the effect of anti-ultraviolet and waterproof functions. The thickness of the lens is related to the refractive index of the material used in the lens. The higher the refractive index of the lens, the thinner it is. The so-called ultra-thin lens is the lens with a high refractive index. From the side view of the lens, there will be a fuzzy color phenomenon. Because the nearsighted lens is a concave lens, and the edge is similar to a prism, which can produce a prism effect. In addition, when you wear glasses, try to choose a smaller frame, so you can avoid the prism effect on the edge of the lens.
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