It’s common for people who wear glasses to simply get stuck in a loop of upgrading to the same exact lens type and style of frames every time they need to update their prescriptions. However, sticking to what’s familiar isn’t always necessarily what’s best for our vision, comfort or budget. One of the first things to do when considering a lens change or upgrade is to identify what’s not working about the current lens situation. For instance, you may be tired of replacing cracked lenses every time you misplace them. Or if you’re an avid jogger or cyclist, you might need lenses that protect you from harmful UV rays. You may even dislike the added UV coating that is necessary for the specific lens type you use. You may also simply suspect that a “blur” issue is minimizing the optical performance of your lens.
It’s possible that you’re simply using lenses that are not the optimal option for your frames, prescription intensity or lifestyle needs. Luckily, glasses wearers have options – Glass, Plastic CR-39, Polycarbonate, High-index 1.67, and High-index 1.74.
The two most widely preferred lensesare CR 39 and polycarbonate. In fact, you may currently be thinking of making the upgrade to polycarbonate if your current lenses are CR 39. Is it worth the upgrade? Let’s explore the pros, cons and considerations to keep in mind as you choose between CR 39 and polycarbonate lens options.
CR-39 Lenses
CR-39 lenses are considered to be the most basic and mainstream option. They are actually a more lightweight, easily maintained alternative to actual glass lenses. Unfortunately, true glass lenses are known to drop and shatter rather easily due to their very heavy and fragile nature. You may not actually be able to tell the difference between glass and CR 39 lenses with a quick glance. The optical quality is extremely similar. The big difference is that a CR lens is about half the weight of a glass lens. What’s more, the CR option is much more resistant to shattering. The other obvious benefit is that CR 39 is generally a much cheaper option than anything that will offer comparable results. Here’s a rundown of the pros of going with a CR 39 lens option:
- Affordable.
- Lighter than glass.
- Good optic clarity.
- Relatively easy to tint.
- UV coating can be applied.
- Scratch-resistant coating can be applied.
- Low distortion from dispersion or chromatic aberration.
The CR 39 design is also proven. In fact, these lenses have been popular since 1947. Of course, this won’t be the right lens for everyone. There are some factors that simply make a CR lens a less than ideal fit for some glasses wearers. Here’s a rundown of the cons of the CR lens:
- UV protection is not inherent.
- Scratches somewhat easily.
- Cannot be used for rimless and semi-rimless glasses.
- Only recommended for those with “weak” prescriptions (under +/-4.00D).
- Heavier than other plastic options.
The bottom line on the CR-lens is that it is a great option for many. However, it’s not necessarily a universal option that’s going to provide maximum benefit for all glasses wearers. It’s definitely a suitable option for those with lighter prescriptions who are looking for “fashion” glasses. It’s still important to review options for upgrading to something slightly more durable and versatile
Polycarbonate Lenses
It’s worth giving polycarbonate a glance if it’s time to upgrade your lenses. Like CR-39, polycarbonate has been a popular choice for decades. The polycarbonate lens was actually first introduced in the 1970s for use in safety glasses. The lens material was actually developed for use in helmet visors used by the Air Force prior to being used on the commercial market. Polycarbonate was a popular option for “civilian” glasses by the 1980s. It is considered to be a premier option for lenses today.
Polycarbonate
offers a higher index of refraction than CR-39. The breakdown is 1.586 versus 1.498. This means that a wearer can get a measurably thinner lens using the exact same prescription. The other big benefit to polycarbonate is that it has a notably higher level of impact resistance than CR-39. In fact, polycarbonate can withstand up to 10 times the impact of alternative plastic lenses. That doesn’t mean that a polycarbonate lens is indestructible. It simply means that there’s a better chance of a lens maintaining its integrity against certain types of impact. This is one of the reasons why you’ll see polycarbonate preferred by people who work in rigorous environments or play sports. This type of lens is also commonly used in professional or safety glasses. Additionally, it is a popular option for children’s frames.
Polycarbonate also earns points over something like CR-39 because of the way it naturally blocks UV light. That means that glasses wearers can avoid the extra processing time and costs associated with having a UV coating applied. The last major perk related to polycarbonate has to do with style. This is generally the preferred option for rimless frames. That’s because the crack-resistance and pliability of this lens type actually makes the process of drilling holes a little easier for technicians. There is generally less risk of lenses cracking during the fitting process if the lenses are made from polycarbonate. That doesn’t mean polycarbonate is always the only option for rimless frames. However, this material is simply a good fit for rimless designs. Here’s a little list of why polycarbonate lenses are great:
- Affordable.
- Lighter than Plastic CR-39.
- Works for most prescriptions.
- Relatively easy to tint.
- Available in all prescriptions and lens options – like polarized and transitions.
Polycarbonate certainly offers many advantageous features and qualifies. However, that doesn’t make it the perfect fit for everyone. Here’s a rundown of some of the potential cons to remember when considering a polycarbonate lens:
- More expensive than CR-39.
- May be prone to more visual disturbances/blur than CR-39.
- Almost always requires the application of a scratch-resistant coating.
It is important to cover the detail that polycarbonate is often associated with blur or reduced optic quality for some wearers. It’s important to discuss a very basic understanding of how lenses perform to understand why this is the case. This blurring effect that is sometimes experienced with polycarbonate is caused by something called chromatic aberrations. Those aberrations are the results of polycarbonate’s Abbe value of 30. The Abbe value of a lens is the expressed measurement for how widely that lens is able to disperse wavelengths of light as light passes through. It is simply a consequence of the composition of polycarbonate. It’s certainly important to know about this as you move toward making an informed decision about upgrading your prescription lenses. However, it’s also important to know that many people actually adapt very nicely after making the switch to polycarbonate.
Upgrading to polycarbonate is going to provide an automatic advantage for some. For instance, it’s worth strongly considering this lens option for anyone who spends a lot of time cycling, running or training in any capacity. Lens options that are less durable than polycarbonate simply don’t bring the vigor and resiliency needed. Unfortunately, that means a constant cycle of having lenses replaced.
