1.56 vs. 1.61 vs. 1.67 vs. 1.74 Lenses: Which Lens Index Should You Choose?

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.

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

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 Standard Index 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 High Index Lenses

Best for: Moderate prescriptions around ±2.00 to ±5.00.

1.61 High Index lenses provide a thinner and lighter alternative to 1.56 Standard Index 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 1.56 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 Ultra High Index 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 Standard Index lenses for prescriptions up to approximately ±2.00.
• Choose 1.61 High Index lenses for prescriptions around ±2.00 to ±5.00.
• Choose 1.67 High Index lenses for prescriptions around ±5.00 to ±7.00.
• Choose 1.74 Ultra High Index 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 High Index lenses for a thinner appearance, particularly when choosing a larger frame or when the prescription also includes significant astigmatism.

Is the thinnest lens always best? Not necessarily. Higher-index materials generally have a lower Abbe value, which means some wearers may notice slightly more color fringing (faint rainbow edges around bright objects) when looking through the outer parts of the lens. For mild prescriptions, the thickness savings from a higher index are often small, so a lower index may be the more practical choice. For strong prescriptions, the thinner profile usually outweighs this trade-off.

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. Minus (nearsighted) lenses are thickest at the edges, while plus (farsighted) lenses are thickest in the center.
• 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 pupillary distance (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. Our guide on how to choose glasses for a high prescription covers frame size, shape and material in more detail.

How to Choose Your Lens Index When Ordering from Youtop Optical

Lens index is selected as part of your lens options, so you don't need to decide it before you start shopping:

1. Pick a frame. Check its measurements against our Eyeglass Frame Size Guide. If your prescription is strong, a smaller full-rim frame (for example, acetate) helps hide edge thickness.
2. Select your lenses on the product page. After choosing your lens type, you can choose your lens index there. Prescription lenses start from $29.99. The price depends on your lens type (single vision, progressive or non-prescription) and goes up as you choose a thinner, higher index, and you'll see the price of each option as you select your lenses.
3. Match the index to your prescription. Use the ranges above, or the index chart in our Complete Eyeglass Lens & Prescription Guide.

To see what happens after you order, read How We Make Your Glasses. If you're still unsure which index suits your prescription and frame, contact us before ordering and we'll help you decide.

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 1.56 Standard Index or 1.61 High Index lenses, while stronger prescriptions may benefit more noticeably from 1.67 High Index or 1.74 Ultra 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.