Choosing the right lens index is an important part of ordering prescription glasses. The lens index determines how efficiently your lenses bend light and can affect the thickness, weight, and appearance of your glasses.
In this guide, we'll explain what lens index means, compare the different options available, and help you choose the best lens for your prescription.
Table of Contents
What Is Lens Index?
Lens index, also called refractive index, refers to how efficiently a lens bends light. A higher lens index allows the same prescription to be made using less lens material, resulting in thinner and often lighter lenses.
For stronger prescriptions, higher-index lenses can significantly reduce lens thickness and weight, creating a more comfortable and attractive pair of glasses.
However, the highest available lens index is not automatically the best choice for every prescription. Lower prescriptions usually do not require ultra-thin lenses, while stronger prescriptions may benefit more noticeably from a higher-index material.
Lens Index Comparison
| Lens Index | Best For | Recommended Prescription |
|---|---|---|
| 1.56 | Low prescriptions | Up to ±2.00 |
| 1.61 | Moderate prescriptions | Approximately ±2.00 to ±5.00 |
| 1.67 | Strong prescriptions | Approximately ±5.00 to ±7.00 |
| 1.74 | Very strong prescriptions | Approximately ±7.00 and above |
These prescription ranges are general guidelines. The best lens index may also depend on your cylinder value, frame size, lens shape, prescription type, and personal preferences.
Important: Your cylinder (CYL) value for astigmatism can also affect lens thickness. If your prescription includes a higher CYL value, you may benefit from choosing a higher-index lens even if your SPH value falls within a lower range.
Understanding Each Lens Index
1.56 Standard-Index Lenses
Best for: Lower prescriptions up to approximately ±2.00.
1.56 lenses are a reliable and affordable option for many everyday prescriptions. For lower prescriptions, they can provide a comfortable lens profile without the added cost of a higher-index material.
- Affordable everyday option
- Suitable for lower prescriptions
- Good balance of clarity and comfort
- Available with many common lens treatments
1.61 Mid-Index Lenses
Best for: Moderate prescriptions around ±2.00 to ±5.00.
1.61 lenses provide a thinner and lighter alternative to standard lenses, making them a popular choice for customers with moderate prescriptions who want improved comfort and appearance without moving to the highest lens indexes.
- Thinner than standard-index lenses
- Lighter and more comfortable for many prescriptions
- Good balance between price and performance
- Well suited to moderate prescriptions
1.67 High-Index Lenses
Best for: Strong prescriptions around ±5.00 to ±7.00.
1.67 high-index lenses are designed for stronger prescriptions where reducing thickness and weight becomes more important. They can provide a slimmer profile and a less noticeable lens edge compared with lower-index options.
- Noticeably thinner lens profile
- Reduced edge thickness for many nearsighted prescriptions
- Lighter than lower-index options in stronger prescriptions
- Improved cosmetic appearance
1.74 Ultra-High-Index Lenses
Best for: Very strong prescriptions of approximately ±7.00 and above.
1.74 lenses are our thinnest lens option and are designed for customers with very strong prescriptions who want the greatest practical reduction in lens thickness.
- Our thinnest lens material option
- Maximum practical reduction in thickness
- Helpful for very strong prescriptions
- Can improve comfort and appearance when paired with a suitable frame
Which Lens Index Should I Choose?
As a general guideline:
- Choose 1.56 lenses for prescriptions up to approximately ±2.00.
- Choose 1.61 lenses for prescriptions around ±2.00 to ±5.00.
- Choose 1.67 lenses for prescriptions around ±5.00 to ±7.00.
- Choose 1.74 lenses for prescriptions around ±7.00 and above.
These ranges are a starting point rather than strict rules. For example, someone with a prescription near ±4.00 may still prefer 1.67 lenses for a thinner appearance, particularly when choosing a larger frame or when the prescription also includes significant astigmatism.
If you're unsure which lens index is best for your prescription, don't worry. Our team reviews prescriptions before production to help ensure your selected lenses are suitable for your needs.
What Else Affects Lens Thickness?
Lens index is important, but it is not the only factor that determines how thick your finished lenses will be.
- Sphere (SPH): Stronger nearsighted or farsighted prescriptions generally require more lens power and may increase thickness.
- Cylinder (CYL): Higher astigmatism correction can add thickness in certain areas of the lens.
- Frame size: Larger or oversized frames usually require more lens material than smaller frames.
- Frame shape: Certain shapes may require the lens to be cut farther from its optical center.
- Pupillary distance: The relationship between your PD and the frame measurements can affect how much lens material must be removed.
- Frame style: Full-rim acetate frames may conceal thicker lens edges better than thin metal or rimless designs.
For stronger prescriptions, choosing a smaller, well-fitting frame can sometimes make as much difference as upgrading the lens index.
Final Thoughts
The right lens index can make your prescription glasses thinner, lighter, and more comfortable to wear. Lower prescriptions are often well served by standard or mid-index lenses, while stronger prescriptions may benefit more noticeably from 1.67 or 1.74 high-index options.
At Youtop Optical, we offer multiple lens index options so you can choose the right balance of clarity, comfort, appearance, and value. When your order is reviewed, our team can also check whether the selected lens option is appropriate for your prescription and frame.