The short answer: High-index lenses use a denser material that bends light more, so a strong prescription is ground thinner and lighter than standard plastic. The higher the index number, from 1.50 up to 1.74, the thinner the lens at the same power. They matter most for strong prescriptions, where they cut the thick-edge look and the weight on your nose.
What the index number means
Index of refraction measures how much a material bends light. A higher number bends light more, so less material does the same correction. Standard plastic sits at 1.50. Move up the scale and the lens gets thinner for the same prescription. The stronger your prescription, the more that thinning shows.
Which index for which prescription
| Index | Best for |
|---|---|
| 1.50 (standard) | Low prescriptions, up to about 2 diopters |
| 1.57 to 1.59 | Mild to moderate, around 2 to 4 |
| 1.60 to 1.67 | Moderate to strong, 4 to 6 |
| 1.74 | Strong prescriptions, 6 and up |
The trade-offs
Thinner lenses cost more as the index climbs. High-index materials also reflect more light, so the lens shows more glare unless you add anti-reflective coating. Pair the two and the lens looks nearly invisible. Skip the coating and you trade thickness for shine. See anti-reflective coating for why they belong together.
Who needs them
If your prescription is mild, standard 1.50 or 1.59 lenses stay thin enough and cost less. If your prescription is strong and your current lenses bulge at the edges or weigh on your nose, high-index is the fix. A smaller frame helps too, because less lens means less thickness at the rim.
From our test bench. We cut the same strong prescription in 1.50 and 1.67 and measure the edge. The 1.67 lens came out clearly thinner at the rim and lighter on the scale. In a thin metal frame that was the gap between lenses sitting flush and lenses standing proud of the rim. Strong prescriptions are where the money shows.
FAQ
Are high-index lenses worth it?
For strong prescriptions, yes. They cut thickness and weight that standard lenses cannot. For mild prescriptions the difference is small and standard lenses are the better value.
Do high-index lenses need anti-reflective coating?
They benefit from it more than any other lens, because the dense material reflects more light. Adding AR removes that extra glare and makes the thin lens look clear.
What is the thinnest lens available?
1.74 is the thinnest common index. It suits the strongest prescriptions and costs the most. Above a certain power it is the only option that keeps lenses slim.
Part of Sunglasses Lenses Guide · Related: anti-reflective coating · Browse eyeglasses · Last updated: August 5, 2026
