The Basics of Eyeglasses
For most people, eyeglasses remain the preferred choice for vision correction, despite innovations in contact lenses and vision correction surgery. Eyeglasses are both a means of vision correction and a fashion item, and there are more choices than ever in frame and lens materials and frame styles, shapes and colors. Options abound, including hypoallergenic frame materials for people with sensitive skin and frames made with highly flexible metal alloys, which reduce the possibility of breakage. Spring hinges are another popular feature for added durability, especially for children’s eyewear.
Often the best choice is to select more than one pair of eyeglasses to complement your lifestyle and wardrobe. Multi-colored inlays, composite materials, designer emblems, and enhancements such as insets of precious stones are popular features in many of today’s frame styles. Rimless styles are an understated way to wear eyeglasses without obvious frames. In these styles, plastic or metal temples attach directly to the lenses rather than onto a rim surrounding the lenses.
You also have many options when choosing lenses for your eyeglasses. Popular eyeglass lens designs and materials include:
Aspheric lenses, which have a slimmer, more attractive profile than other lenses and eliminate that magnified, “bug-eye” look caused by some prescriptions.
High index lenses, which are made of special plastic materials that enable the lenses to be noticeably thinner and lighter than regular glass or plastic lenses.
Polycarbonate lenses are thinner, lighter and up to 10 times more impact-resistant than regular plastic lenses. These lenses are great for safety glasses, children’s eyewear, and for anyone who wants lightweight, durable lenses.
Photochromic lenses are sun-sensitive lenses that quickly darken in bright conditions, and quickly return to a clear state in ordinary indoor lighting.
Polarized lenses reduce glare from flat, reflective surfaces (like water) for greater viewing comfort outdoors and less eye fatigue.
Anti-reflective (AR) coating is beneficial for virtually all eyeglass lenses, particularly high index lenses that reflect more light than conventional glass or plastic lenses. AR coating eliminates distracting lens reflections and reduces glare for better visibility for night driving. Other lens coatings include scratch-resistant, ultraviolet treatment, and mirror coatings for sunglasses.
Presbyopia is the normal, age-related loss of near focusing ability that makes reading and other close-up tasks more difficult after age 40. The primary symptom of presbyopia is the need to hold reading material farther away to see it clearly. Eventually, presbyopia worsens to the point that bifocal or other multifocal eyeglass lenses are needed. Multifocal eyeglass lenses available for presbyopia correction include:
Bifocals : These lenses have two powers – one for distance and one for near – separated by a visible line.
Trifocals : These multifocal lenses have three powers for seeing at varying distances – near, intermediate and far – separated by two visible lines.
Progressive lenses : These lenses have many lens powers that gradually change with no visible lines. Because they have no lines, progressive lenses allow a smooth, comfortable transition from one distance to another.
If you’ve never needed glasses to see clearly prior to the onset of presbyopia, simple reading glasses with single vision lenses may be all you need to restore your near vision. But reading glasses are for near vision only, and objects across the room will appear blurred through the lenses.
When choosing eyeglasses, be sure to consider your appearance, personal taste and lifestyle as well as your eyeglass prescription needs. A professional optician can help you choose frames and lenses that both complement your appearance and satisfy your lifestyle and vision needs.
Each eyeglass frame material offers its own advantages and style features. For eyewear that fits every occasion in your life, consider purchasing more than one pair of glasses and choose a different frame material for each pair.
For example, you may want one pair of glasses with metal frames for a conservative, professional look for work. But on weekends, you may want something with more color or style, like a zyl frame in laminated colors, or a combination frame with a modern spin of a classic retro-style.
Most people who purchase eyeglasses prefer the timeless appearance of metal frames. There are many types of metal you can choose, and each has its own distinctive properties.
Stainless steel : This is an iron-carbon alloy that also contains chromium. Stainless steel frames are lightweight, strong, durable, flexible and corrosion-resistant. They can be produced in matte or polished finishes.
Titanium : This premium metal is very strong, durable, corrosion-resistant, and is 40% lighter than other metals. It’s also hypoallergenic, making it titanium frames an excellent choice for anyone with sensitive skin. Titanium frames are available in several colors.
Beta titanium : This is an alloy of predominantly titanium, with small amounts of aluminum and vanadium. These other metals in the alloy make beta titanium more flexible than frames made of pure titanium for easier fitting adjustments.
Memory metal : This is a titanium alloy composed of roughly 50 percent titanium and 50 percent nickel. Memory metal eyeglass frames are extremely flexible, and can be twisted or bended and still return to their original shape. This feature makes memory metal frames a great choice for kids and anyone who is hard on their glasses.
Beryllium :This lower-cost alternative to titanium resists corrosion and tarnishing, making it an excellent choice for anyone with high skin acidity or who spends a good amount of time in or around salt water. Beryllium frames also are lightweight, strong, flexible and are available in a wide range of colors.
Monel : This popular, inexpensive material is an alloy of nickel and copper. Monel is less costly than other metals, but – depending on the quality of the plating used – monel frames can cause skin reactions in some individuals over time.
Zyl : This very popular frame material (also called Zylonite or cellulose acetate) is a lightweight and relatively inexpensive type of plastic. Zyl frames are available in a wide variety of colors, including multi-colored models and frames with different layers of color.
Propionate : This is a nylon-based plastic that is strong, flexible, lightweight and hypoallergenic. Propionate often is used in frames for sports eyeglasses because of its durability.
Nylon : This frame material is still occasionally used. Nylon is strong, lightweight and flexible, but it can become brittle with age. For this reason, it has for the most part been replaced by nylon blends – polyamides, copolyamides and gliamides – which are more durable.
Combination frames Combination frames have both metal and plastic components. Popular in the 1950s and 1960s, combination frames have made a comeback recently, in a wide variety of colors that give classic models a more modern look.
Lens Options for Eyeglasses
Nearly everyone can benefit from thinner, lighter lenses. High-index plastic lenses can be up to 50 percent thinner than regular glass or plastic lenses, and they’re usually much lighter, too. Though high-index lenses are especially beneficial if you have a strong eyeglasses prescription, they can make a noticeable difference in the appearance of virtually any pair of glasses. High-index lenses bend light more efficiently than regular glass or plastic lenses, so less lens material is required to correct your vision.
There is a range of high-index lenses to choose from, each having a different price point based on how much thinner the lenses are compared with regular plastic lenses. All high-index lenses are classified by their “index of refraction” (or “refractive index”). Generally lenses with a higher index of refraction will be thinner (and usually more expensive) than lenses with a lower index. The index of refraction of regular plastic lenses is 1.50. The refractive index of high-index plastic lenses ranges from 1.53 to 1.74. Those in the range of 1.53 to 1.59 are about 20 percent thinner than regular plastic lenses, whereas 1.74 high index lenses are up to 50 percent thinner than regular plastic lenses.
High-index lenses are available in virtually all lens designs (single vision, bifocal, progressive, photochromic, etc.) and your professional optician can advise you regarding the combination of lens material and design that best fits your needs and budget. Note: High-index lenses reflect more light than regular glass or plastic lenses, so anti-reflective (AR) coating is highly recommended for these lenses (see below).
To make high-index lenses even more attractive, most of them have an “aspheric” design. This means that instead of having a round (or “spherical”) curve on the front surface, these lenses have a curve that gradually changes from the center to the lens to the periphery. This makes aspheric lenses noticeably flatter for a slimmer, more attractive lens profile. Aspheric lenses are particularly beneficial if you are farsighted. The flatter profile of aspheric lenses greatly reduces the magnified, “bug-eye” look caused by regular, highly curved lenses for farsightedness, and they greatly reduce the “bulge” of the lenses from the frame.
Because of their slim profile, aspheric lenses also have less mass, making them much lighter than conventional eyeglass lenses. Aspheric lenses also provide superior peripheral vision compared with conventional lenses. Note: Because they have flatter curves than regular lenses, aspheric lenses may cause more noticeable reflections. Anti-reflective (AR) coating is recommended for these lenses (see below).
Polycarbonate and Trivex lenses are special lightweight high-index lenses that offer superior impact resistance. These lenses are up to 10 times more impact resistant than regular plastic lenses, making them an ideal choice for children’s eyewear, safety glasses, and for anyone with an active lifestyle who wants a thinner, lighter, safer lens. Polycarbonate lenses have a refractive index of 1.59, making them 20 to 25 percent thinner than regular plastic lenses. They also are up to 30 percent lighter than regular plastic lenses, making them a good choice for anyone who is sensitive to the weight of eyeglasses on their nose.
Trivex lenses may be slightly thicker than polycarbonate lenses in some prescriptions, but they provide comparable impact resistance and, like polycarbonate lenses, they block 100 percent of the sun’s harmful UV rays.
All eyeglass lenses reflect some light, reducing the amount of light that enters the eye to form visual images. This can affect your vision, especially under low-light conditions such as driving at night. Lens reflections also cause glare, further reducing vision in these situations. The amount of light reflected from eyeglass lenses depends on the lens material. Conventional glass or plastic lenses reflect about 8 percent of incident light, so only 92 percent of available light enters the eye for vision. Thinner, lighter high-index lenses reflect up to 50 percent more light than regular glass or plastic lenses and therefore can cause more problems with glare unless something is done to reduce reflections.
Anti-reflective (AR) coating reduces lens reflections and allows more light to enter the eye for better night vision. Regardless of the lens material, eyeglass lenses with AR coating transmit more than 99 percent of available light to the eye. By eliminating surface reflections, anti-reflective coating also makes your lenses nearly invisible. This greatly improves the appearance of your eyewear and allows others to see your eyes, not the reflections in your glasses.
Be sure to use only products recommended by your optician when cleaning lenses with anti-reflective coating. Because AR coating eliminates reflections that hide small scratches, you’ll want to take care not to scratch AR-coated lenses, as scratches on these lenses may be more visible than scratches on uncoated lenses.
No eyeglass lenses — not even glass lenses — are scratch-proof. However, lenses that are treated front and back with a clear, hard coating are more resistant to scratching, whether it’s from dropping your glasses on the floor or occasionally cleaning them with a paper towel. Kids’ lenses, especially, benefit from scratch-resistant coatings.
Nearly all high-index lenses (including polycarbonate) come with a factory-applied scratch-resistant coating for added durability. This coating is optional for regular plastic lenses. However, to safeguard your eyewear investment, scratch-resistant coating should be considered for all eyeglass lenses. The only exception is glass lenses, which are naturally hard and scratch-resistant.
To further protect your eyeglasses from scratches, keep them in a protective case when you’re not wearing them. Also, never clean your lenses without first rinsing them with water or an approved cleaning solution. Rubbing a dry, dusty or dirty lens with a cleaning cloth or towel can cause scratches, even if the lens is treated with a scratch-resistant coating.
Just as you use sunscreen to keep the sun’s UV rays from harming your skin, UV treatment for eyeglass lenses blocks those same rays from damaging your eyes. Overexposure to ultraviolet light is thought to be a cause of cataracts, retinal damage and other eye problems. Most high-index lenses have 100 percent UV protection built-in. But with regular plastic lenses, a lens treatment is required for these lenses to block all UV rays. This UV treatment does not change the appearance of the lenses and is quite inexpensive.
Photochromic lenses are convenient indoor-outdoor eyeglass lenses that automatically darken to a sunglass shade outside when exposed to sunlight, and then quickly return to a clear state indoors. Photochromic lenses also provide 100 percent protection from the sun’s UV rays and are available in a wide variety of lens materials and designs, including bifocal and progressive lenses. The amount of darkening that most photochromic lenses undergo depends on how much UV radiation they are exposed to. As a general rule, these lenses won’t get as dark inside a car or truck because the glass windshield blocks out much of the sun’s UV rays that cause the lenses to change color. For driving on sunny days, polarized sunglasses usually are the best solution to reduce glare and improve visibility.
With so many new lens products available, it’s hard to know all your options and decide which lenses are best for you. A professional optician can make selecting your eyeglasses easy and fun and help you find the perfect eyewear for your personal style and vision requirements.
Discuss your visual needs with your optician!
Nearly everyone can benefit from specialty eyewear. Be sure to discuss your daily activities with your optician when shopping for eyewear to get the best specialty eyewear solutions for your specific needs.
Though your “everyday” glasses may serve you well for many activities, you can improve your comfort, performance and safety for other specific visual tasks with specialty eyewear. This is especially true if you wear bifocals or progressive lenses due to presbyopia. Here are a few examples of where specialty eyewear provides advantages over everyday glasses:
Eye strain, fatigue and muscle strains are common problems associated with prolonged computer use. “Computer glasses” have lenses that are specially designed to maximize your vision at the intermediate and close-up distances you use during computer work. Computer-specific eyewear will give you the best correction for these distances and reduce your risk of developing computer vision syndrome.
If you wear bifocals, you may find you have to tip your head back slightly to use the reading portion of the lens. This may be fine for some near vision tasks, but if you want to sit and read a novel, this head-back posture can cause neck discomfort and fatigue. Often, a pair of single vision reading glasses is a much better solution for prolonged reading and other prolonged near work, such as sewing or needlepoint.
Lawn mowers, power trimmers, grinding tools and other power tools all can cause serious eye injuries from high-speed projectiles. Even something as simple as hammering a nail can cause flying debris. Safety glasses are a must for these activities. Safety glasses that offer the best protection include polycarbonate lenses and a safety frame with side shields or a close-fitting wrap style.
Did you know that wearing specially-tinted eyeglass lenses can improve your visual acuity on the tennis court, golf course or on the slopes? Sport-specific eyewear can enhance performance by improving visual clarity while protecting your eyes from injury.
Driving glasses can have clear or tinted lenses. If you are under the age of 40 and do not have presbyopia, your everyday glasses usually will work fine for driving at night. But for daytime conditions, it’s wise to have a second pair of polarized lenses with a contrast-enhancing tint to reduce glare and improve visibility. If you are presbyopic, specially designed single vision or multifocal lenses can give you a better field of view for driving than your everyday progressive lenses. Two pairs of driving lenses are best: one pair of polarized sun lenses for daytime driving and a second pair with clear lenses for driving at night. Glasses for night driving should include anti-reflective (AR) coating to reduce the glare from streetlights and oncoming headlights and allow more light to reach your eyes for better vision on dark roadways.Source: Eyeglass Lens Coatings by AllAboutVision.com. Article ©2011 Access Media Group LLC. All rights reserved.