When you go to the eye doctor and get your brand new prescription, the fun task of selecting your new eyewear begins. But picking out your frame is only part of the work involved in getting your new eyewear ordered. The more difficult, yet more important, decisions involve your lenses.
The frame you select is mainly cosmetic, but the lenses and options you choose to go in those frames can affect the way that you see the world.
You will be offered a vast array of lenses and options to select from, and, depending of your prescription, you will most likely be given, at a minimum, the choice between plastic (CR-39) or polycarbonate (aka, “poly”) lenses. Which ones should you choose?
This decision is part cosmetic, part optical/visual, part price, and part durability. Let’s address these issues one at a time:
- Cosmetic- Unless your prescription is fairly minimal (the sphere “sph,” or first number on your prescription, is less than a -2.00), you will notice that polycarbonate lenses are thinner than plastic lenses. In a thick, plastic frame, this difference may not be noticeable, but in a thin wire, rimless, or semi-rimless style, the difference will be more obvious. Generally, we recommend you start considering a thinner lens option at a prescription of around -2.50 or above. Lenses for patients with a (+) prescription will find that their lenses are thicker in the center and thinner around the edges (unlike patients with a (-) prescription, whose lenses are thin in the middle and thicker around the edges), and so the “polycarbonate = thinner” concept does not apply to them.
- Optical/Visual- Because polycarbonate is a denser type of plastic material than “standard”/CR-39 plastic lenses, it can actually slow down light passing through the lens more than the standard plastic lens, causing what is known as “chromatic aberrations” around the edges of the lenses. Chromatic aberration is when a lens begins split light into its component colors like a prism. So some wearers of polycarbonate lenses notice a color “halo” around light colored objects, the horizon, etc. This is quite uncommon, and even someone who notices it initially can usually adjust to the lenses simply by wearing them for a week or two straight.Plastic lenses, because they are thicker, tend to be heavier than a polycarbonate lens in the same exact prescription, so someone with a higher prescription should seriously consider this lens type for the sake of their nose!Polycarbonate lenses, even clear ones, are 100% UV protectant.
- Price- Because polycarbonate is considered an “upgraded” lens option, it usually costs a bit more than plastic. Many insurances will either cover this upgrade, or give a discount on it, especially for individuals under the age of 18.
- Durability- Because, as we mentioned earlier, polycarbonate is more dense than plastic, it tends to be much more scratch resistant. All polycarbonate lenses are hard coated as part of the finishing process of manufacturing the lens. It also tends to crack less than plastic lenses, so people getting semi-rimless (no frame on the bottom part of the lens) or rimless/drill mount glasses should consider polycarbonate at a minimum (although high-index lenses and trivex lenses are actually better for the drill mount frame styles).
We recommend that children and people who have active/hazardous jobs or hobbies should be in polycarbonate or trivex lenses exclusively. The reason for this is that, given the right conditions, a plastic lens could shatter into a patient’s eyes, while a polycarbonate or trivex lens is shatter-resistant, and is therefore safer.
We hope that this helps make your lens selection process a bit easier! Stay tuned for upcoming editions of “Eyeglass Lens Options” where we will discuss topics including Anti-Reflective (AR) Coatings, Trivex Lenses, the Pros and Cons of Transitions Lenses, and more!