A Buying Guide For Eyeglasses
Created Exclusively by Eyeglass.com, © 2012
Can you explain the sizing of eyeglass frames?
Eyeglass frame sizes traditionally come in three dimensions, measured in millimeters, which can typically be found either on the inside of the frame temple or on the nose bridge.
An example of an eyeglass frame size is: 48-20-145
The first measurement (48 in this case) refers to the horizontal width of one lens at its widest point.
The second measurement (20) refers to the width of the nose bridge, the metal or plastic piece that connects the two lenses.
The third measurement (145) refers to the entire length of one temple, the piece that extends from the front of the eyeglass frame to behind your ear.
You can fit into a variety of glasses sizes depending on the style of the frames, and most frames are at least somewhat adjustable. Keep in mind that just because 48-20-145 may have been a nice fit in one frame, 48-20-145 in another frame may fit you completely differently due to small discrepancies in the frame design. These dimensions are foremost a resource for opticians in laboratories but they are also the only eyeglass frame sizing available to the public, which is why it is readily used. Use the frame dimensions as a loose guideline to find the perfect fit.
What are the basic types of frame styles?
There are many different types of frames, highlighted below are the three most basic types: rimless, semi-rimless, and rimmed.
Rimless eyeglasses have become increasingly popular over the last couple of years, although rimmed eyeglasses are the most common. Rimless eyeglasses have no metal or plastic material surrounding the lenses. The temples and nose-bridge are typically drilled and mounted straight onto the lenses through screws, bolts, or gromets. Therefore, rimless glasses must use durable lenses, polycarbonate or trivex, to withstand the drilling and prevent chipping. Rimless glasses are known for their light weight, but the lenses are generally more expensive and the glasses more delicate than other styles. For an example of a rimless frame click here.
Semi-Rimless eyeglasses typically have metal or plastic material around the upper part of the lenses, leaving the bottom part of the lens rimless. Like rimless frames, polycarbonate or trivex lenses are strongly suggested to withstand drilling on the lenses. However, with semi-rimless, as an alternative to drilling, the eyeglasses can be held in place by a filament, similar to fishing line, which goes into the grove making it invisible. Aesthetically, with semi-rimless glasses, the framed rim follows the eyebrows so it is not as noticeable but the naked edge is on the bottom where it is more visible, making the semi-rimless a trendy style. For an example of a semi-rimless frame click here.
Rimmed eyeglasses are the most common. They have material, either plastic or metal or a combination of the two, all the way around the lens. Rimmed glasses are classically more durable and not as delicate as the other options because the lenses are more protected. Rimmed glasses are also a good option for people who have a strong prescription because they are better at hiding the thickness of the lens. For an example of a rimmed frame click here.
Keep all of these factors in mind when picking out eyewear to match your style, budget, and prescription!
How do I know which lens material to choose?
When it comes to choosing lens material, it is important to keep in mind their advantages and disadvantages. The lens materials highlighted below are regular plastic (CR-39), polycarbonate, trivex, and glass.
Regular plastic, also known as CR-39, is the material that most lenses are made out of. CR-39 is typically used in full-rimmed frames and covers the middle range of almost all prescriptions. CR-39 has the best clarity next to glass and tends to be the least expensive out of the lens materials. However, regular plastic is slightly more fragile than polycarbonate and trivex and with CR-39, the higher the prescription, the thicker the plastic. If you have a low prescription, for example between -2 and +2 or if you can function without your glasses, then chances are that CR-39 is fine for you and you would be wasting your money to pay for thinner lenses. Unlike polycarbonate, regular plastic lenses are cast, which means that they pour liquid plastic into a mold and it’s cured through chemistry to form a solid lens but it’s not under any pressure.
Polycarbonate is a type of plastic that is thinner and lighter than the other materials and the most shatter resistant of all of the materials besides trivex. Therefore, polycarbonate can be used for all types of eyeglasses: rimmed, rimless, and semi-rimless. Polycarbonate is highly recommended anyone under 18, active kids, athletes, or anyone in a labor-intensive work environment. One of the reasons that polycarbonate is shatter resistant is that it is really soft, so it must have a scratch coating. You cannot get polycarbonate without scratch-coating. Therefore, if you are charged for scratch-coating when buying polycarbonate lenses, it’s an unnecessary charge. Polycarbonate was the original material for bullet-proof vests, which is why it is good for safety lenses. So imagine you have a screw-driver, and you hit the lens as hard as you can, it would simply stick in the polycarbonate. Whereas in any other material, the screw-driver could crack the lens. On the downside, polycarbonate does tend to scratch a little easier than regular plastic and is slightly more expensive. Polycarbonate lens is molded under high pressure in an injection molding machine so a disadvantage is that the vision you get through the lens is slightly worse than CR-39 and trivex which are not cast molded. For most people they would never notice this different, but for those who are very sensitive, they might want to consider CR-39 or trivex over polycarbonate.
Trivex is a new formula of polycarbonate and one of the newest types of lenses. Trivex has almost all of the attributes of polycarbonate, but it is slightly more expensive, lighter in weight, and has more stability for drilling for semi-rimless and rimless. Polycarbonate is also slightly thinner than trivex and available in a wider selection of lens designs. Trivex, like CR-39, is cast not molded, so there is better optical clarity.
Glass is the material that all lenses were originally made out of, however the heaviness of glass and the cost of manufacturing has led to a shift towards plastic materials for frame lenses. Glass is so heavy that it puts pressure on the nose and can even leave marks on the skin. It takes special equipment to make glass lenses and few labs carry the equipment, therefore glass lenses tend take longer to manufacture. Some people report clear transmission with glass because the light transmission is actually better than plastic. Although, scratch coatings can be very good for plastics, some people feel that glass is more scratch-resistant. Glass tends to be the most stable material; it doesn't flex and has almost no distortion.
Note: There are three kinds of prescriptions: - and +. The majority of people have a – prescription, meaning they are near-sighted. The stronger the negative (-) prescription, (-1.0 is relatively low, -8.5 is very high), the thicker the edge of the lens is. As the lens gets bigger because of the width of the frame, the edge also gets bigger. Therefore, it is possible that if you have a high prescription and are near-sighted, getting a smaller frame (with a reduced width) could shed some money off the total price of the glasses. For those who are near-sighted, the stronger the positive (+) prescription, (+1 is relatively low, +8.5 is very high), the thinner the lenses are on the edge and the thicker it is in the center. The main effect of having a strong positive prescription is that because a plus lens actually magnifies, it makes your eyes look bigger behind the lenses and getting a thinner material will not change that, no matter what material you use.
Overall, the differences in material are related to thickness, visual acuity, and impact resistance. So, when choosing a lens material, keep in mind the type of frame you want, your prescription, and your budget.
How can I save money when buying prescription sunglasses?
Summer sun begs sunglasses and if someone needs prescription lenses in their sunglasses the cost can get pretty high. Since the choices can seem daunting and too technical, we have come up with a simple buying guide for prescription sunglasses.
Prescription Sunglasses are a mix of fashion and health - safety and fun. From a medical standpoint, it is important to block the part of the light spectrum that can be harmful. Evidence correlates UV exposure to cataracts, macular degeneration, and other eye health issues. The good news is that certain lenses and coatings block portions of the light spectrum. Understanding what the choices are can protect eyesight and save money.
Light is measured in nanometers, for example, the visible spectrum is between 390 and 750 nanometers. The portion of the spectrum that can be most harmful is UVA 320-400 nanometers. Much of the harmful light is not visible to the human eye, but can still cause serious harm. When nonprescription sunglass lenses are marked UV 400 that means they block up to 400 nm and are safe to wear. A question often asked at eyeglass.com is, "How do you know when sunglasses block harmful UV light?" according to founder Jim Morrison.
Here is a trick, wear sunglasses with polycarbonate (poly) lenses, the material automatically blocks the dangerous spectrum. No coating needed. If a patient is charged extra for UV coating on poly lenses it is unnecessary. It would be like ordering a sandwich and being charged extra for the bread. Similarly, polycarbonate lenses are impact resistant without any further treatment. In fact, several states require opticians to use polycarbonate lenses for sports and children under 18.
Another trick with poly lenses is that they automatically come with a scratch coating, so don't pay extra for that either. Poly lenses are also thinner than standard lenses. So, why don't all Rx sunglasses lenses come with polycarbonate? Although poly has a scratch coating they are still not as scratch resistant as standard plastic and poly is more expensive to make and harder to process. Poly may not be the best lens material choice for wearers who are not so careful with their glasses. And one more detail, poly lenses don't have the same visual clarity as standard plastic lenses. This last point is somewhat subjective. According to eyeglass.com's licensed optician, Lorenzo Rodgers of Bay View Opticians, "The science is real, poly doesn't have the better light transmission, but most people can not tell the difference. That being said, if you are sensitive and notice slight vision changes, avoid polycarbonate lenses."
Poly has UV blocking, thinness, impact resistant, and scratch coating included. The negative is that poly is still scratch prone, more expensive, and has lower visual clarity than other plastic or glass lenses. Just when a buyer thought they could translate glasses lingo, another term pops up - anti-reflective coating. What once seemed like a cosmetic option is now considered a wise, medical choice. AR coating on a sun lens, especially on the backside of the lens, reduces UV exposure by keeping unfiltered light from bouncing off the back lens and into a person's eyes. Additionally, backside anti-reflective coating helps with enhancing visual clarity.
When it comes to tinted lenses the color does make a difference. Grey colored lenses have the least effect on natural color, brown sun lenses are soothing and yellow does not shade much but helps with contrast and is therefore good for sports sunglasses.