THIN IS IN

High-index, demystified: 1.67 vs 1.74, when thinner is worth the money, and how to cheat thickness for free.

High-index lenses do one thing: bend light more efficiently, so less material is needed to hit your prescription. The number — 1.67, 1.74 — is the refractive index. Higher number, thinner lens. Standard plastic sits around 1.50, so jumping to 1.67 cuts noticeable thickness, and 1.74 cuts more. But thinner is not automatically better, and the price jumps are real.

Here's the honest breakdown. For mild to moderate prescriptions (roughly up to ±3.00), high-index is mostly cosmetic — your lenses are already reasonably thin, and the money buys you millimeters. Between ±3.00 and ±6.00, 1.67 is the sweet spot: visibly thinner, lighter on the nose, worth it for most wearers. Past ±6.00, 1.74 earns its price — at those powers, standard lenses get genuinely thick and heavy, and high-index is the difference between glasses you wear and glasses you tolerate. One caveat: higher index means lower Abbe value, meaning slightly more chromatic fringe at the edges. Pair high-index with good anti-reflective coating and the trade-off mostly disappears.

But the cheapest thickness reduction isn't a material at all — it's the frame. Smaller lens openings mean thinner edges, because lens thickness grows with diameter. Round and oval shapes hide edge thickness better than big rectangles. Full rims conceal the edge entirely; rimless and semi-rimless put it on display. Center the prescription in the frame — decentration adds thickness — and consider aspheric designs, which flatten the curves and slim the profile further.

So the formula: right index for your power, small frame, full rim, aspheric design. Do all four and even a strong prescription can look like off-the-shelf glasses. *Talk to your eye doctor about which index your prescription actually needs.*

"The thinnest lens is a small frame away. Material is only half the trick."