Why Your Optician Keeps Talking About Lens Materials (And Why It Actually Matters)
When you order glasses, your optician asks you to choose a lens material. Most people shrug and pick whatever sounds reasonable. CR-39, polycarbonate, high-index, Trivex — the names don't mean much if nobody explains the tradeoffs. But the material you choose affects how thick your lenses are, how clear they look, how heavy they feel on your face, and how well they hold up over time.
Here's what each option actually does, and when each one makes sense.
CR-39: The Standard That Still Works
CR-39 is the original plastic lens material, developed in the 1940s and still widely used. It has excellent optical clarity — meaning the image you see through the lens is sharp and undistorted. It's also the most affordable option.
The tradeoff is thickness. CR-39 has a lower refractive index (1.50), which means lenses need to be thicker to achieve the same prescription power as higher-index materials. For prescriptions up to about +/- 2.00, this isn't noticeable. Beyond that, lenses start getting visibly thick, especially at the edges for nearsighted prescriptions.
Good for: Low to moderate prescriptions, backup pairs, budget-conscious orders where optical quality matters most.
Polycarbonate: Impact Resistance First
Polycarbonate is significantly more impact-resistant than CR-39. It's the standard for children's glasses, safety eyewear, and sport frames for this reason. It's also thinner than CR-39 at the same prescription (refractive index 1.59) and inherently blocks UV light without needing a separate coating.
The downside is optical quality. Polycarbonate has a higher Abbe value dispersion, which in plain terms means it can create more chromatic aberration — slight colour fringing at the edges of your vision, especially with stronger prescriptions. Most people don't notice this, but if you're sensitive to optical quality or have a high prescription, it can be bothersome.
Good for: Kids, athletes, anyone in a work environment where eye protection matters, rimless or semi-rimless frames that need a tough lens.
Trivex: The Best of Both (Almost)
Trivex was developed as an improvement over polycarbonate. It matches polycarbonate's impact resistance but offers better optical clarity (lower chromatic aberration). It's also the lightest lens material available, which makes a real difference in all-day comfort, especially with larger frames.
The tradeoff is cost — Trivex lenses are typically more expensive than both CR-39 and polycarbonate. They're also slightly thicker than polycarbonate at the same prescription, though the difference is minimal.
Good for: Anyone who wants the safety of polycarbonate with better optics, people sensitive to lens weight, drill-mount (rimless) frames.
High-Index: Thin Lenses for Strong Prescriptions
High-index lenses (1.67 and 1.74 are the most common) bend light more efficiently, meaning they can achieve the same prescription power with less material. The result is noticeably thinner, lighter lenses — especially important for prescriptions beyond +/- 4.00 where standard materials produce thick, heavy lenses.
Higher refractive index does come with more light reflection off the lens surface, which is why anti-reflective coating is essentially mandatory with high-index lenses. Without it, you get distracting reflections and reduced contrast. The lenses are also more brittle than polycarbonate or Trivex, so they're not ideal for sport frames or young children.
Good for: Moderate to strong prescriptions where thickness and weight are concerns, anyone who wants the thinnest possible profile.
1.67 vs 1.74: Is the Upgrade Worth It?
For most people, 1.67 high-index provides a good balance of thinness and value. The jump to 1.74 gives you roughly 10-15% thinner lenses, which is noticeable primarily with very strong prescriptions (beyond +/- 6.00). Below that threshold, the visual difference between 1.67 and 1.74 is minimal, and the cost difference is significant.
What About Glass?
Actual glass lenses still exist and offer the best scratch resistance and optical clarity of any material. But they're heavy, they shatter (creating a safety hazard), and very few labs still process them. Glass lenses are essentially a specialty item now, occasionally used for very specific applications but not recommended for everyday wear.
How We Choose at the Lab
When an optician sends us a lens order, the material choice is already made — but we see patterns in what works well. Strong prescriptions in CR-39 come back thick and heavy. Polycarbonate in high prescriptions sometimes gets complaints about edge distortion. High-index without anti-reflective coating always looks worse than it should.
The material choice isn't just about what's "best" in the abstract. It's about matching the material to the prescription strength, the frame type, the patient's lifestyle, and their visual sensitivity. A proper recommendation considers all of these.
If you're an optician looking for a lab that can advise on material selection or process specialty lens orders, get in touch. We work with the full range of materials and can help you find the right match for your patients.