The lenses you choose for your spectacles — even more than frames — frequently will identify how delighted you are with your eyewear.
Best Eyeglass Lenses Buyers Guide
And buying eyeglass lenses is not an easy task. In reality, in a current concern, Consumer Reports publication stated, “There are many choices for lenses and coverings, it’s simple to be puzzled about what’s worth buying.”
This buying guide will help you cut through the hype about different types of eyeglass lenses and assist you choose lenses and coatings that use the best features and value for your requirements.
Why Choosing The Right Eyeglass Lenses Is So Important
When buying spectacles, the frame you choose is important to both your appearance and your comfort when wearing glasses. However the eyeglass lenses you choose influence 4 factors: appearance, comfort, vision and safety.
A typical error individuals frequently make when purchasing spectacles is not investing adequate time considering their choices of spectacles lens materials, designs and finishings.
This article provides you the basics you need to know to buy glasses lenses carefully.
The following details uses to all prescription lenses for glasses — whether you need single vision lenses to remedy nearsightedness, farsightedness, and/or astigmatism, or you need progressive lenses, bifocals or other multifocal lenses to likewise remedy presbyopia.
Glasses Lens Materials – Features And Benefits
Glass lenses. In the early days of vision correction, all eyeglass lenses were made from glass.
Although glass lenses offer exceptional optics, they are heavy and can break easily, potentially triggering serious harm to the eye and 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 light-weight plastic glasses lenses. The lenses were made from a plastic polymer called CR-39, an abbreviation for “Columbia Resin 39,” due to the fact that it was the 39th solution of a thermal-cured plastic developed by PPG Industries in the early 1940s.
Because of its light weight (about half the weight of glass), low cost and excellent optical qualities, CR-39 plastic stays a popular material for eyeglass lenses even today.
Polycarbonate lenses. In the early 1970s, Gentex Corporation presented the first polycarbonate lenses for shatterproof glass. Later on that years 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 considerably more impact-resistant than CR-39 plastic, making it a preferred product for children’s glasses, safety glasses and sports eyewear.
A more recent lightweight glasses lens material with comparable impact-resistant properties as polycarbonate is called Trivex (PPG Industries), which was presented for eyeglasses in 2001. A potential visual benefit of Trivex is its higher Abbe value (see below).
High-index plastic lenses. In the past 20 years, in reaction 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 likewise have a lower specific gravity.
See also: High Index Lenses
Eyeglass Lens Materials
Here are popular spectacles lens products, arranged in order of refractive index and lens density (respectable indications of cost). Other than for the crown glass, these are all plastic products.
|Lens Material||Refractive Index||Abbe Value||Key Features and Benefits|
|High-index plastics||1.70 to 1.74||36 (1.70) |
|The thinnest lenses available. |
Block 100 percent UV.
|High-index plastics||1.60 to 1.67||36 (1.60) |
|Thin and lightweight. |
Block 100 percent UV.
Less costly than 1.70-1.74 high-index lenses.
|Tribrid||1.60||41||Thin and lightweight. |
Significantly more impact-resistant than CR-39 plastic and high-index plastic lenses (except polycarbonate and Trivex).
Higher Abbe value than polycarbonate.
Downside: Not yet available in a wide variety of lens designs.
|Polycarbonate||1.586||30||Superior impact resistance. |
Blocks 100 percent UV.
Lighter than high-index plastic lenses.
|Trivex||1.54||45||Superior impact resistance. |
Blocks 100 percent UV.
Higher Abbe value than polycarbonate.
Lightest lens material available.
|CR-39 plastic||1.498||58||Excellent optics. |
|Crown glass||1.523||59||Excellent optics. |
Downsides: heavy, breakable.
Index Of Refraction
The index of refraction (or refractive index) of a spectacles lens product is a number that is a relative measure of how efficiently the material refracts (bends) light, which depends on how quick light travels through the product.
Particularly, the refractive index of a lens product is the ratio of the speed of light in a vacuum, divided by the speed of light in the lens product.
For example, the index of refraction of CR-39 plastic is 1.498, which suggest light journeys roughly 50 percent slower through CR-39 plastic than it does through a vacuum.
The greater the refractive index of a material, the slower light relocations through it, which results in greater bending (refracting) of the light rays. So the higher the refractive index of a lens product, the less lens product is needed to flex light to the exact same degree as a lens with a lower refractive index.
Simply puts, for a provided eyeglass lens power, a lens made of a product with a high refractive index will be thinner than a lens made from a product with a lower refractive index.
The refractive index of current spectacles lens materials ranges from 1.498 (CR-39 plastic) to 1.74 (a particular variety of high-index plastic). So for the same prescription power and lens design, a lens made of CR-39 plastic will be the thickest lens readily available, and a 1.74 high-index plastic lens will be the thinnest.
See also: Eye Exam: Time, Preparation and Cost
The Abbe value (or Abbe number) of a lens product is an unbiased step of how commonly the lens disperses various wavelengths of light as light go through it. Lens materials with a low Abbe worth have high dispersion, which can cause noticeable chromatic aberration — an optical mistake visible as colored halos around items, especially lights.
When present, chromatic aberration is most visible when browsing the periphery of glasses lenses. It is least visible when looking directly through the central optical zone of the lenses.
Abbe worths of glasses lens materials vary from a high of 59 (crown glass) to a low of 30 (polycarbonate). The lower the Abbe number, the most likely the lens material is to cause chromatic aberration.
Abbe number is called after the German physicist Ernst Abbe (1840-1905), who defined this beneficial procedure of optical quality.
In addition to selecting a lens material that has a high index of refraction, another way to give your lenses a slimmer, more appealing profile is to select an aspheric style.
Aspheric designs — where the lens curvature modifications gradually from the center of the lens to its edge — enable lens makers to use flatter curves when producing eyeglass lenses, without breaking down the optical performance of the lenses.
Due to the fact that aspheric lenses are flatter than standard (round) lens designs, they cause less unwanted zoom of the wearer’s eyes, for a much better appearance. In many cases, aspheric designs also enhance the clearness of the wearer’s peripheral vision.
Many high index plastic lenses are made with aspheric designs to optimize both the look and the optical efficiency of the lenses. With polycarbonate and CR-39 lenses, an aspheric design normally is a choice that increases the cost of the lenses.
Minimum Center Thickness (Or Edge Thickness)
The FDA has guidelines for impact resistance, so there’s a limitation to how thin an optical lab 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 fix farsightedness, the thinnest portion of the lens is at its edges.
Because of their superior effect resistance, polycarbonate and Trivex lenses that fix myopia can be produced to a center density of simply 1.0 mm and still pass the FDA impact-resistance requirement. Myopia-correcting lenses made from other materials typically have to be thicker in the center to pass the standard.
The size and shape of your eyeglass frames likewise will affect the thickness of your lenses, specifically if you have a strong prescription. Choosing a smaller sized, well-centered frame can significantly decrease the thickness and weight of your lenses, despite the lens material you select.
Usually, the thinnest lenses for your prescription will be aspheric lenses made of a high-index material, worn in a small frame.
Also read: Understanding Eye Prescriptions
Eyeglass Lens Treatments
For the most comfy, durable and best-looking glasses, the following lens treatments must be thought about vital:
Anti-scratch coating. All light-weight eyeglass lens materials (see table) have surface areas that are significantly softer and more susceptible to scratches and abrasions than glass lenses. The softest spectacles lens is also the one that is the most impact-resistant: polycarbonate. But all plastic and high-index plastic lenses require a factory-applied anti-scratch coating for appropriate lens toughness.
Most of today’s contemporary anti-scratch coatings (likewise called scratch coats or difficult coats) can make your spectacles lenses nearly as scratch-resistant as glass. But if you’re difficult on your glasses or you’re buying eyeglasses for your kids, inquire about lenses that consist of a guarantee versus scratches for a specific period of time.
Anti-reflective coating. An anti-reflective (AR) coating makes all eyeglass lenses better. AR finishings remove reflections in lenses that minimize contrast and clearness, particularly during the 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 likewise much less most likely to have glare spots in photographs.
Anti-reflective coating is especially essential if you choose high-index lenses, because the greater the refractive index of a lens material, the more light the lenses reflect. In fact, high-index lenses can show approximately 50 percent more light than CR-39 lenses, causing substantially more glare, unless AR coating is used.
UV-blocking treatment. Cumulative direct exposure to the sun’s damaging ultraviolet (UV) radiation over a person’s lifetime has actually been related to age-related eye issues including cataracts and macular degeneration.
For this reason, people ought to secure their eyes from UV start in early youth. Luckily, polycarbonate and almost all high-index plastic lenses have 100 percent UV defense built-in, due to absorptive attributes of the lens product.
But if you choose CR-39 plastic lenses, know that these lenses need an added coating used to supply equal UV protection afforded by other lens materials.
Photochromic treatment. This lens treatment enables eyeglass lenses to darken instantly in response to the sun’s UV and high-energy visible (HEV) light rays, and after that rapidly go back to clear (or almost clear) when indoors. Photochromic lenses are offered in virtually all lens materials and designs.
Cost Of Eyeglass Lenses And Eyeglasses
Depending upon the kind of lenses and lens treatments you select and the lens style you require, your glasses lenses can quickly cost more than the frames you pick — even if you select the current designer frames.
So how much will your glasses cost? That’s hard to say.
Inning accordance with Consumer Reports’ newest reader survey released in 2013, participants spent a mean of $244 out-of-pocket on their last set of prescription glasses. However this figure can be misleading.
The amount you spend for your next set of glasses will depend upon many factors, including your visual requirements, your fashion desires and whether you have vision insurance that covers a portion of the cost of your glasses.
Remember that if you pick high-end designer frames and aspheric, high-index progressive lenses with premium anti-reflective coating, it’s not unusual for the cost of your glasses to go beyond $800.
On the other hand, if you’re purchasing your child’s first pair of prescription spectacles with polycarbonate lenses for moderate myopia, the cost will be much closer to $200 for quality glasses, including a scratch-resistant guarantee.
To get the best value, it’s vital to comprehend the functions and benefits of the items you are thinking about and to pick carefully with the assistance of a trusted eye care company and/or eyeglasses retailer.
When Buying Eyeglass Lenses, There’s No Substitute For Expert Advice
Purchasing glasses lenses can appear difficult, but it does not need to be. The secret is getting accurate, impartial eyeglass lens information from sources you can trust. To discover an optometrist near you, click on this link.
For greatest fulfillment with your glasses, in addition to using this guide, follow this guidance echoed by Consumer Reports: During your eye exam, ask your optometrist which eyeglass lenses and lens treatments are best for your particular needs and glasses prescription.