What Is a Lens Index?
The lens index (also called refractive index) is a number that describes how efficiently a lens material bends light. A higher index means the material bends light more efficiently — so the lens can be made thinner while still providing the same optical correction.
1.50 (Standard Plastic / CR-39)
The baseline. Lightweight, excellent optical clarity, and affordable. Suitable for prescriptions up to approximately ±2.00D. Beyond that, lenses become noticeably thick at the edges.
1.60 (High Index)
Recommended for prescriptions in the ±2.00 to ±4.00 range. Noticeably thinner and lighter than 1.50. Anti-reflective coatings are standard and essential at this index.
1.67 (Higher Index)
Ideal for prescriptions from ±4.00 to ±6.00. Significantly thinner — many people with higher prescriptions move to this index for aesthetic and comfort reasons.
1.74 (Ultra-High Index)
The thinnest plastic lens available. Recommended for very high prescriptions (±6.00 and above). These are more expensive and more fragile — handle with care and use quality frames.
Practical Guidance by Prescription
- Up to ±2.00: 1.50 is fine
- ±2.00 to ±3.00: 1.56 or 1.60
- ±3.00 to ±5.00: 1.60 or 1.67
- ±5.00 and above: 1.67 or 1.74
Don't Forget Coatings
A higher-index lens without coatings performs worse in some ways — higher-index materials inherently reflect more light. An anti-reflective (AR) coating is essential for 1.60 and above.