Eyeglass Lens Index Guide | Generated by AI
Understanding Refractive Indices in Eyeglass Lenses: 1.56, 1.60, and 1.67
The numbers 1.56, 1.60, and 1.67 refer to the refractive index (often just called “lens index”) of the material used in eyeglass lenses. This is a measure of how efficiently the lens material bends light to correct your vision. A higher refractive index means the lens can bend light more effectively, allowing for thinner and lighter lenses—especially important for stronger prescriptions where lenses would otherwise become bulky.
Here’s a quick breakdown of each:
| Lens Index | Common Use Case | Thickness Benefit | Typical Prescription Range |
|---|---|---|---|
| 1.56 | Standard plastic lenses (e.g., polycarbonate alternatives) | Baseline thickness; good for everyday wear | Low to moderate (up to about -4.00 to -6.00 diopters for myopia) |
| 1.60 | Mid-index lenses (e.g., Trivex or improved plastic) | About 15-20% thinner than 1.56 | Moderate (around -4.00 to -8.00 diopters) |
| 1.67 | High-index lenses (e.g., advanced polycarbonate) | 30-50% thinner than 1.56; up to 40% thinner than standard for high prescriptions | High/strong (over -6.00 to -10.00+ diopters) |
These indices are for single-vision lenses (correcting one field of vision). Higher indices like 1.67 are pricier and may have slightly more chromatic aberration (color fringing), but coatings can minimize this.
Why 1.67 Is Associated with High or “Deep” Myopia
A 1.67 index doesn’t “mean” high myopia—myopia (nearsightedness) is defined by your prescription strength in diopters (e.g., -6.00 or higher is considered high myopia). Instead, it’s recommended for high/deep myopia because:
- Strong negative prescriptions (like -8.00) require lenses that curve more at the edges to focus light properly, making them thick and heavy with standard materials (e.g., 1.56 index).
- A higher index like 1.67 bends light sharper, so the lens doesn’t need as much material to achieve the same correction. This results in thinner edges (up to half the thickness of a 1.50 index lens for the same prescription), reducing weight, distortion, and the “coke-bottle” look.
In short: For mild myopia (-2.00), a 1.56 lens is fine and affordable. But for deep myopia (-7.00+), 1.67 (or even 1.74) makes the glasses practical and stylish by keeping them slim.
How It Makes Thinner Eyeglasses
- Physics basics: Light bends more in denser materials (higher index = denser). For myopia, the lens diverges light; a high-index material does this with less bulk.
- Example: At -5.00 diopters, a 1.56 lens might be 4mm thick at the edge, while 1.67 could be ~2.5mm—noticeably slimmer and lighter.
- Trade-offs: Higher indices can be more brittle and reflective (anti-reflective coatings help), but they’re ideal if comfort and aesthetics matter.
If your prescription is known, an optician can recommend the best index. Always get a professional fitting for the thinnest possible result.
References
- Lens index guide for glasses: What index is best for me?
- High-index lenses: Transform thick glasses to thin glasses
- 1.56 vs 1.6 vs 1.67 vs 1.74 Lenses: How to Choose
- How to Choose the Refractive Index of Lenses for Different Degrees of Myopia
- What is the meaning of lens 1.56