High Index Lenses: When Thinner Is Worth Paying For
If your prescription is stronger than -4.00 or +3.00, standard lenses get thick. The edges bulge out of the frame. High index lenses compress the same prescription into a thinner, flatter lens. Here is when the upgrade makes sense and when it doesn't.
What Is Lens Index?
Index measures how efficiently a lens material bends light. Higher index means the lens can be thinner while doing the same job. Standard plastic (CR-39) has an index of 1.50. High index starts at 1.61 and goes up to 1.74.
Every step up in index shaves about 15-20% off lens thickness. Someone with a -6.00 prescription could go from 6mm edge thickness in standard lenses to about 3.5mm in 1.67 high index. That is the difference between lenses that fit flush in the frame and lenses that stick out.
Index Comparison Table
| Index | Best For | Thickness vs Standard | Cost at Fytoo |
|---|---|---|---|
| 1.50 (Standard) | Mild Rx (-2.00 to +2.00) | Baseline | Free |
| 1.61 | -3.00 to -5.00 | ~20% thinner | $15-30 |
| 1.67 | -5.00 to -8.00 | ~35% thinner | $30-50 |
| 1.74 | -8.00 and stronger | ~45% thinner | $50-80 |
When to Upgrade
If your prescription is under -3.00, the thickness difference is barely visible. Save your money. Between -4.00 and -6.00, 1.61 or 1.67 is worth it if you care about how the glasses look from the side. Above -6.00, 1.67 or 1.74 is almost necessary to keep the lenses inside the frame.
Frame choice matters too. Thin metal frames expose lens edges. Thick acetate frames hide them. If you wear bold plastic frames, you can get away with a lower index. If you want rimless or thin titanium, go higher index.
Affiliate link · We earn a commission at no extra cost to you
FAQ
Is 1.74 high index worth it?
Only if your prescription is stronger than -8.00. The difference between 1.67 and 1.74 is small - maybe 10% thinner. Below -8.00, the extra cost is hard to justify. Above -8.00, every bit of thickness reduction helps with weight and appearance.
Do high index lenses have more glare?
Yes, slightly. Higher index materials reflect more light off the lens surface. That is why anti-reflective coating matters more with high index lenses - it cuts the reflections. Fytoo includes AR coating standard, so this is handled.
Can I get high index with progressives?
Yes. If you need both strong correction and multiple distances, high index progressives are the best combination. They cost more but the lens will be thin across all three zones.