CR-39: The Oldest and Still the Undefeated King of Optical Lenses

My journey into the world of eyewear didn’t start with a medical textbook; it began with a paintbrush. Back in 1996, I walked into a local optical shop simply to help them design and paint advertising posters. To support my education, I stayed on to work part-time. That split-second decision reshaped the next three decades of my life.

I spent my first six months behind the sales counter, learning how to connect with people and understand their visual struggles. But my heart was drawn to the back of the shop—the lens edging workshop.

In the late 1990s, heavy glass lenses were still the dominant mainstream choice, but lightweight plastic resin lenses were just beginning to disrupt the market. The very first resin material I laid my hands on was what we in the trade affectionately called "White Lenses" (Uncoated Clear Lenses). Back then, anti-reflective coatings were an absolute luxury. These raw, uncoated lenses possessed a breathtaking, water-like transparency. While natural glass always carried a faint yellowish-brown or pale green tint, this new resin was brilliantly, flawlessly white.

That material was CR-39.

In those days, automatic lens-edging machines were rare, expensive luxuries. Crafting a pair of glasses required raw human skill. To shape a CR-39 resin lens, we didn't press a button on a computer; we used specialized hand-shears (scissors) to carefully snip the circular lens into the rough shape of the frame. One wrong snip, and the lens was ruined. We then stood at a manual grinding wheel for hours, meticulously shaping and smoothing the edges by hand until it snapped perfectly into the rim.

For the older glass lenses, the process was even more tense—we used a diamond-tipped glass cutter to score the surface, snapped the excess away piece by piece, and slowly ground down the razor-sharp perimeter.

This intense, tactile training taught me a fundamental lesson: a great pair of glasses is not mass-produced by a machine; it is born from the precise harmony of a craftsman’s hands and the material he holds.

It is crucial to understand a major distinction that corporate marketing often blurs: CR-39 is not the only definition of a resin lens; it is simply the glorious pioneer of the organic resin family. Today, factories churn out dozens of newer plastic materials with higher refractive indexes to make lenses thinner, but in the realm of pure physics, newer does not mean better.

When commercial optical chains sell you a lens today, they talk about thinness or unbreakable hardness. True optical experts talk about the Abbe Value.

Named after the physicist Ernst Abbe, this physical constant measures the optical clarity and color dispersion of a material. The higher the Abbe value, the lower the chromatic aberration (color blurring and distortion at the outer edges), and the more relaxed your eyes will be.

Look at how the physics stack up against the physical limit of nature:

Over the years, the market has introduced newer materials like Polycarbonate, hyping them up as "space-age" upgrades because they are tough enough to survive a hammer blow. But as any material scientist will tell you, hardness and toughness are two entirely different concepts that exist in a delicate trade-off.

While Polycarbonate is highly impact-resistant, it is optically flawed, soft, easily scratched, and possesses an incredibly low Abbe value that forces your brain to constantly fight peripheral distortion—leading to chronic eye fatigue and headaches.

In daily optical clarity, all new materials are a compromise in front of CR-39.

Of course, to be completely transparent with you, CR-39 is not a magical solution for every single person. In physics, every material has its limitations. CR-39 possesses a low refractive index of 1.50, meaning it is strictly suitable only for low to moderate prescriptions.

If you have a very strong prescription (high myopia or astigmatism), crafting your lenses out of CR-39 would result in edges that are far too thick and heavy for comfort. For these higher prescriptions, advanced High-Index Resin lenses (such as premium MR-8 or polyurethane-based materials with indexes of 1.60, 1.67, or 1.74) become necessary. These modern, high-index organic resins use complex chemical structures to bend light more efficiently, allowing the lenses to be incredibly thin and lightweight. While they sacrifice a small amount of Abbe value compared to CR-39, they represent the absolute best, most comfortable compromise for high prescriptions.

When I opened my independent practice and later founded TAKEMOTO, I carried the spirit of that 1996 workshop with me. I chose to reject commercial trend-chasing. For anyone within low to moderate prescription ranges, CR-39 remains my absolute gold standard. It honors the core purpose of eyewear: to grant you the most flawless, comfortable, and natural vision possible.

Artisan eyewear isn't about using the newest industrial plastic; it's about knowing which time-tested materials truly respect the human eye.