High-index lenses: do you need 1.67 or 1.74?
What high-index lens numbers mean, when 1.67 or 1.74 is worth it, and why frame size matters more than you think. A plain-English guide from Phoenix opticians.
If your prescription is strong, someone has probably offered you high-index lenses. The numbers sound technical, so here is what they actually mean.
What the number means
The index is how strongly a material bends light. Standard plastic is about 1.50. The higher the number, the less material it takes to do the same job, so the lens can be thinner. 1.67 and 1.74 are the two most common high-index plastics.
When it is worth it
- Under about plus or minus 3.00: standard plastic, Trivex or polycarbonate is usually fine.
- Around -4.00 to -8.00: 1.67 is the sweet spot for most people.
- Past about -8.00: 1.74 starts to make a visible difference at the edges.
Try our lens thickness tool to see how your prescription compares across materials.
The thing nobody tells you
For a minus prescription, edge thickness grows fast with frame width. A smaller, rounder frame in 1.67 can end up thinner than a big frame in 1.74. That is why we talk about frames and lenses together, not separately. It is a big part of what we do for complex prescriptions.
Always add anti-reflective coating
Higher index materials reflect more light. Without a good anti-reflective coating, high-index lenses can look shiny and show more glare. We consider it part of the lens, not an extra.
