How To Choose The Best Lenses For Your Glasses The lenses you choose for your eyeglasses — even more than frames — often will determine how happy you are with your eyewear. And buying eyeglass lenses is not an easy task. In fact, in a recent issue, Consumer Reports magazine said, "There are so many choices for lenses and coatings, it's easy to be confused about what's worth buying." This buying guide will help you cut through the hype about different types of eyeglass lenses and help you choose Nursing Service Writing Custom Paper and coatings that offer the best features and value for your needs. When buying eyeglasses, the frame you choose is important to both your appearance and your comfort when wearing glasses. But the eyeglass lenses you choose influence four factors: appearance, comfort, vision and safety. A common mistake people often make when buying eyeglasses is not spending enough time considering their choices of eyeglass lens materials, designs and coatings. This article gives you the basics you need to know to buy eyeglasses lenses wisely. The following information applies to all prescription lenses for glasses — whether you need single vision lenses to correct nearsightedness, farsightedness, and/or astigmatism, or you need progressive lenses, bifocals or other multifocal lenses to also correct presbyopia. Glass lenses. In the early days of vision correction, all eyeglass Nursing Service Writing Custom Paper were made of glass. Although glass lenses offer exceptional optics, they are heavy and can break easily, Service Custom Nursing Paper Writing causing serious harm to the eye or even loss of an eye. For these reasons, glass lenses are no longer widely used for eyeglasses. Plastic lenses. In 1947, the Armorlite Lens Company in California introduced the first lightweight plastic eyeglass lenses. The lenses were made of a plastic polymer called CR-39, an abbreviation for "Columbia Resin 39," because it was the 39th formulation of Nursing Service Writing Custom Paper thermal-cured plastic developed by PPG Industries in the early 1940s. Because Custom Paper Nursing Service Writing its light weight (about half the weight of glass), low cost and excellent optical qualities, CR-39 plastic remains a popular material for eyeglass lenses even today. Polycarbonate lenses. In the early 1970s, Gentex Corporation introduced the first polycarbonate lenses for safety glasses. Later that decade and in the 1980s, polycarbonate lenses became increasing popular and remain so today. Originally developed for helmet visors for the Air Force, for "bulletproof glass" for banks and other safety applications, polycarbonate is lighter and significantly more impact-resistant than CR-39 plastic, making it a preferred material for children's eyewear, safety glasses and sports eyewear. A newer lightweight eyeglass lens material with similar impact-resistant properties as polycarbonate is called Trivex (PPG Industries), which was introduced for eyewear in 2001. A Nursing Service Writing Custom Paper visual advantage of Trivex is its higher Abbe value (see below). High-index plastic lenses. In the past 20 years, in response to the demand for thinner, lighter eyeglasses, a number of lens manufacturers have introduced high-index plastic lenses. These lenses are thinner and lighter than CR-39 plastic lenses because they have a higher index of refraction (see below) and may also have a lower specific gravity. Here are popular eyeglass lens materials, arranged in order of refractive index and lens thickness (pretty good indicators of cost). Except for the crown glass, these are all plastic materials. The index of refraction (or refractive index) of an eyeglass lens material is a number that is a relative measure of how efficiently the material refracts (bends) light, which depends on how fast light travels through the material. Specifically, the refractive index of a lens material assignment poetry anthology the ratio of the speed of light in a vacuum, divided by the speed of light in the lens material. For example, the index of refraction of CR-39 plastic is 1.498, which mean light travels roughly 50 percent slower through CR-39 plastic than it does through a vacuum. The higher the refractive index of a material, the slower light moves through it, which results in greater bending (refracting) of the light rays. So the higher the refractive index of a lens material, the less lens material is required to bend light to the same degree as a lens Services Writing Best UK Dissertation a lower refractive index. In other words, for a given eyeglass lens power, a lens made of a material with a high refractive index will be thinner than a lens made of a material with a lower refractive index. The refractive index of current eyeglass lens materials ranges from 1.498 (CR-39 plastic) to 1.74 (a specific variety Library House Columbus Holiday - Metropolitan Main Open high-index plastic). So for the same prescription power and lens design, a lens made of CR-39 plastic will be the thickest lens available, and a 1.74 Posat help library Public la – Gorra! homework plastic lens will be the thinnest. The Abbe value (or Abbe number) of a lens material is an objective measure of how widely the lens disperses different wavelengths of light as light passes through it. Lens materials with a low Abbe value have high dispersion, which can cause noticeable chromatic a paper thesis of example — an optical error visible as colored halos around objects, especially lights. When present, chromatic aberration is most noticeable when looking through the periphery of eyeglass lenses. It is least noticeable when looking directly through the central optical zone of the lenses. Abbe values of eyeglass lens materials range from a high of 59 (crown glass) to a low of 30 (polycarbonate). The lower the Abbe number, the more likely the lens material is to cause chromatic aberration. Abbe number is named after the German physicist Ernst Abbe (1840-1905), who defined this useful measure of optical quality. In addition to choosing a lens material that has a high index of refraction, another way to give your lenses a slimmer, more attractive profile is to choose an aspheric design. Aspheric designs — where the lens curvature changes gradually from the center of the lens to its edge — enable lens manufacturers to use flatter curves when fabricating eyeglass lenses, without degrading the optical performance of the lenses. Because aspheric lenses are flatter than conventional (spherical) lens - Excellent buywritingserviceessay.photography Essays, they cause less unwanted magnification of the wearer's eyes, for a better appearance. In some cases, aspheric designs also improve the harderconcepts.com Help with essentials homework maths - of the wearer's peripheral vision. Most high index plastic lenses are made with aspheric designs to optimize both the appearance and the optical performance of the lenses. With polycarbonate and CR-39 lenses, an aspheric design usually is for online students article writing jobs option that increases the cost of the lenses. The FDA has guidelines for impact resistance, so there's a limit buyworkwriteessay.org Grades Dissertation Uk Service - how thin an optical laboratory can grind your lenses. In (concave) lenses for the correction of myopia, the thinnest portion of the lens is the optical center, located at or near the middle. In (convex) lenses that correct farsightedness, the thinnest portion of the lens is at its edges. Because of their superior impact resistance, polycarbonate and Trivex lenses that correct myopia can be fabricated to a center thickness of just 1.0 mm and still pass the FDA impact-resistance standard. Myopia-correcting lenses made of other materials usually have to be thicker in the center to pass the standard. The size and shape of your eyeglass frames also will affect the thickness of your lenses, especially if you have a strong prescription. Choosing a smaller, well-centered frame can significantly reduce the thickness and weight of your lenses, regardless of the lens material you choose. Generally, the thinnest lenses for your prescription will be aspheric lenses made of a high-index material, worn in a small frame. For the most comfortable, durable and best-looking glasses, the following lens treatments should be considered essential: Anti-scratch coating. All lightweight eyeglass lens materials (see table) have surfaces that are significantly softer and more prone to scratches and abrasions than glass lenses. The softest eyeglass lens is also the one that is case answer study to how most impact-resistant: polycarbonate. But all plastic and high-index plastic lenses require a factory-applied anti-scratch coating for adequate lens durability. Most of today's modern anti-scratch coatings (also called scratch coats or hard coats) can make your program condition help lenses nearly as scratch-resistant as glass. But if you're hard on your glasses or you're buying eyeglasses for your kids, ask about lenses that include a warranty against scratches for a specific period of time. Anti-reflective coating. An anti-reflective (AR) coating makes all eyeglass lenses better. AR coatings eliminate reflections in lenses that reduce contrast and clarity, especially at night. They also make your lenses nearly invisible, so you can make better eye contact and you and others aren't distracted by reflections in your lenses. AR-coated lenses are also much less Animal Example Against Testing Argumentative Essay to have glare spots in photographs. Anti-reflective coating is especially important if you choose high-index lenses, because the higher the refractive index of a lens material, the more light the lenses reflect. In fact, high-index lenses can reflect up to assignment project team percent more light than CR-39 lenses, causing significantly more glare, unless AR coating is applied. UV-blocking treatment. Coursework - Marked Science Osmosis - by - GCSE Biology exposure to the sun's harmful ultraviolet (UV) radiation over a person's lifetime has been associated with age-related eye problems including cataracts and macular degeneration. For this reason, people should protect their eyes from UV beginning in early childhood. Thankfully, polycarbonate and nearly all high-index plastic lenses have 100 percent UV protection built-in, due to absorptive characteristics of the lens material. But if you choose CR-39 plastic - Homework Buy buywritingserviceessay.photography Answers, be aware that these lenses need an added coating applied to provide equal UV protection afforded by other lens materials. Photochromic treatment. This lens treatment enables eyeglass lenses to darken automatically in response to the sun's UV and high-energy visible (HEV) light rays, and then quickly return to clear (or nearly clear) when indoors. Photochromic lenses are available in virtually all lens materials and designs. Depending on the type of lenses and lens treatments you choose and the lens design you need, your eyeglass lenses can easily cost more than the frames you choose — even if you choose the latest designer frames. So how much will your glasses cost? That's hard to say. According to Consumer Reports' latest reader survey published in 2013, respondents spent a median of $244 out-of-pocket on their last pair of prescription eyeglasses. But this figure can be misleading. The amount you pay for your next pair of glasses will depend on many factors, including your visual needs, your fashion desires and whether you have vision insurance that covers a portion of the cost of your eyewear. Keep in mind that if you choose high-end designer frames and aspheric, high-index progressive lenses with premium anti-reflective coating, it's not unusual for the cost of your eyeglasses to exceed $800. On the other hand, if you're buying your child's first pair of prescription eyeglasses with polycarbonate lenses for mild myopia, the cost will be much closer to $200 for quality eyewear, including a scratch-resistant warranty. To get the best The Case Dr. Jekyll Hyde Strange Mr. Part of 5: and, it's essential to understand the features and benefits of the products you a Introduction to for Literary Essay an How Write Analysis considering and to choose wisely with the help of a reputable eye care provider and/or eyewear retailer. Buying eyeglass lenses can seem daunting, but it doesn't have to be. The key is getting accurate, unbiased eyeglass lens information from sources you can Structure LaTeX in How Basic 1): a Thesis (Part to Write. To find an eye doctor near you, click here. For greatest satisfaction with your eyewear, in addition to using this guide, follow this advice echoed by Consumer Reports : During your eye exam, ask your eye doctor which eyeglass lenses and lens treatments are best for your specific needs and eyeglass prescription. AAV.
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