What Is Lens Index?
Lens index — also called refractive index — is a number that describes how efficiently a lens material bends light. The higher the index, the more light is bent by the material per millimeter of thickness. This means that for the same corrective power, a higher-index lens requires less material, resulting in a thinner, lighter lens.
The index is expressed as a decimal — for example, 1.50, 1.61, 1.67, or 1.74. The standard index for regular plastic lenses (called CR-39) is 1.50. Everything above that is considered a "high index" material.
Why does thickness matter? Because a thick lens does not just look cosmetically unappealing — it can also distort your vision at the edges (peripheral aberrations), add unwanted weight to your nose and ears, and magnify or minify your eyes in ways that look unnatural to others. Thinner lenses solve these problems at a cost premium.
The 4 Common Lens Indexes Compared
The following table summarizes the key differences between the four most commonly available lens indexes.
| Index | Thickness vs 1.50 | Typical Abbe Value | Weight Reduction | Recommended SPH Range | Price Premium |
|---|---|---|---|---|---|
| 1.50 | Baseline (standard) | 58 (excellent) | Baseline | ±0.00 to ±3.00 | $0 (base) |
| 1.61 | ~20% thinner | 36 (very good) | ~15% lighter | ±3.00 to ±5.00 | +$20–$50/lens |
| 1.67 | ~30% thinner | 32 (good) | ~25% lighter | ±5.00 to ±8.00 | +$50–$100/lens |
| 1.74 | ~40% thinner | 32–34 (good) | ~35% lighter | Above ±8.00 | +$100–$200/lens |
What Is Abbe Value?
Abbe value (named after German physicist Ernst Abbe) measures a lens material's tendency to produce chromatic aberration — the separation of white light into its component colors at the edges of a lens. This can appear as color fringing, particularly when you look through the peripheral areas of a lens.
The higher the Abbe value, the clearer and more optically pure the vision. Here is how the indexes compare:
| Lens Index | Abbe Value | Optical Quality Rating | Notes |
|---|---|---|---|
| 1.50 (CR-39) | 58 | Excellent | Best optical clarity; industry benchmark |
| 1.53 (Trivex) | 43–45 | Very Good | Impact-resistant; great for active lifestyles |
| 1.59 (Polycarbonate) | 30–31 | Good | Highly impact-resistant; used for children's glasses and safety glasses |
| 1.61 | 36 | Very Good | Good balance of thinness and optical quality |
| 1.67 | 32 | Good | Moderate color fringing at edges for some wearers |
| 1.74 | 32–34 | Good | Thinnest available; some color fringing possible |
For most people, the difference between 36 and 58 Abbe is imperceptible in daily life. However, people who are very sensitive to optical distortions, or who do a lot of night driving, may notice slight color fringing with 1.67 and 1.74 lenses.
Which Index for Your Prescription?
The right lens index depends primarily on your prescription strength. The decision tree below helps you choose, but your optician may also recommend a specific index based on your frame choice and pupillary distance.
By Sphere (SPH) Value
| Your SPH Prescription | Recommended Index | Why |
|---|---|---|
| ±0.00 to ±2.50 | 1.50 | Minimal thickness; best optical clarity at lowest cost |
| ±2.75 to ±4.00 | 1.61 | Noticeably thinner without sacrificing optical quality |
| ±4.25 to ±6.00 | 1.61 or 1.67 | 1.67 preferred for round or semi-rimless frames |
| ±6.25 to ±8.00 | 1.67 | 1.67 provides meaningful thickness reduction |
| ±8.25 to ±10.00 | 1.67 or 1.74 | 1.74 gives best cosmetic result; 1.67 more affordable |
| Above ±10.00 | 1.74 | The only index that keeps lenses manageable in thickness |
By Cylinder (Astigmatism) Value
High astigmatism (CYL) also increases lens thickness, particularly in the axis perpendicular to your astigmatism meridian. If your CYL is above -2.00, consider moving up one index level compared to what your SPH alone would suggest.
| Your CYL Value | Index Adjustment | Example SPH + Adjustment |
|---|---|---|
| CYL 0 to -1.00 | No adjustment | Follow SPH-only recommendation |
| CYL -1.25 to -2.00 | Consider +1 index level | SPH -3.00 + CYL -1.50 → use 1.61 or 1.67 |
| CYL -2.25 and above | Move up +1 index level | SPH -4.50 + CYL -2.50 → use 1.67 minimum |
The Trade-offs of High Index Lenses
Going to a higher index is not a free upgrade. Here are the trade-offs to consider:
Optical Clarity
As index increases, Abbe value decreases. This trade-off is unavoidable — it is a physical property of how high-index materials behave optically. In practice:
- 1.50 (Abbe 58): Best optical clarity. Color separation is essentially zero. The gold standard for vision quality.
- 1.61 (Abbe 36): Very good. Most wearers cannot distinguish this from 1.50 in everyday use.
- 1.67 (Abbe 32): Good. A small percentage of sensitive wearers notice slight color fringing at the lens edges, especially with large frames.
- 1.74 (Abbe 32-34): Good. Similar to 1.67. Anti-reflective coatings can help reduce perceived chromatic aberration.
Cost
High index lenses cost significantly more than standard lenses. Here is a typical price comparison:
| Lens Index | Single Vision Upcharge | Progressive Upcharge | Notes |
|---|---|---|---|
| 1.50 (CR-39) | $0 | $0 | Standard included with most frames |
| 1.61 | $20–$50 | $40–$80 | Best value for mild-to-moderate prescriptions |
| 1.67 | $50–$100 | $80–$150 | Mid-range premium for moderate-to-strong Rx |
| 1.74 | $100–$200 | $150–$300 | Maximum thinness for extreme prescriptions only |
Weight
One common misconception is that high index lenses are always lighter. This is only true for high prescriptions. For mild prescriptions (SPH ±2.00), a 1.50 lens is already thin enough that a 1.61 or 1.67 lens will not be meaningfully lighter — you are just paying for a slightly thinner lens.
Frame Choice Matters
Your frame style significantly affects how thick your lenses will look, regardless of index. This is one of the most underappreciated factors in lens selection.
Full-Rim vs. Rimless Frames
| Frame Type | Thickness Impact | Recommendation |
|---|---|---|
| Full Rim (plastic or metal) | Hides lens edges completely | Can use 1.50 or 1.61 even with moderate Rx; frame conceals thickness |
| Semi-Rimless | Partially exposes lens edge | Use 1 index level higher than SPH alone would suggest |
| Rimless | Lens edges fully exposed | Use highest practical index for any Rx above ±3.00; thickness is completely visible |
Frame Size and Lens Thickness
The physical size of your frame lenses directly affects how thick they will be. A larger lens requires more material at the edges, especially for myopic (minus) prescriptions where the thinnest part is the optical center and the edges are the thickest.
- Small frames (lens width under 46mm): Minimize thickness regardless of index. Best choice for strong prescriptions.
- Medium frames (47–52mm): Standard choice. Use the index recommended by your SPH value.
- Large frames (53–58mm): Increase effective thickness by 10-20% vs. small frames. Consider moving up one index level.
- Oversized frames (59mm+): Significantly increases edge thickness for minus prescriptions. Only use with high index lenses if your Rx is moderate or stronger.
If you have a strong prescription and want large fashion frames, you will need 1.67 or 1.74 lenses to avoid extremely thick edges. Alternatively, choosing smaller frames can reduce the required index level.
Price Comparison by Retailer
Lens index pricing varies significantly between retailers. The table below shows approximate index upcharges (per lens) at major online retailers as of early 2026.
| Retailer | 1.61 Upcharge | 1.67 Upcharge | 1.74 Upcharge |
|---|---|---|---|
| Zenni Optical | $12.95 | $22.95 | $49.95 |
| Warby Parker | $25 | $50 | $100 |
| EyeBuyDirect | $15 | $25 | $55 |
| LensCrafters (in-store) | $40–$80 | $80–$150 | $150–$300 |
| Costco Optical | $25–$40 | $50–$75 | $80–$120 |
Online retailers consistently offer lower prices on high index lenses than brick-and-mortar stores. However, in-store purchases include professional fitting and adjustments, which some wearers prefer.
When NOT to Upgrade to a Higher Index
There are situations where upgrading to a higher index is not worth the cost:
- Mild prescriptions (SPH ±0 to ±3.00): The cosmetic difference between 1.50 and 1.61 is negligible. You are paying extra for almost no benefit.
- Reading glasses or computer glasses: These are typically used for short periods. Optical quality (higher Abbe) matters more than thinness.
- Children's glasses: Kids' frames are small, so even moderate prescriptions rarely need high index lenses. Additionally, polycarbonate (1.59) is preferred for impact resistance regardless of index.
- Backup or spare glasses: If you are ordering a spare pair, save money with 1.50 lenses unless your prescription is moderate or stronger.
- Frames with thick rims: Acetate or thick plastic frames hide lens edges completely, eliminating the main cosmetic benefit of high index lenses.
High Index Lenses and Progressive Addition Lenses (PALs)
If you need progressive lenses (multifocal) with a strong prescription, the case for high index lenses is even stronger. Progressive lenses already have multiple optical zones with varying thickness across the lens surface. A stronger ADD power combined with a strong distance prescription can create very uneven thickness profiles.
For progressive lens wearers:
- SPH above ±3.00 with ADD above +1.50: Consider 1.67 minimum
- SPH above ±6.00 with any ADD: 1.67 or 1.74 recommended
- High-index progressive lenses also tend to have wider corridor designs that work better in smaller frames
Digital freeform progressive lenses (which are surfaced using CNC technology to optimize the optical design for your specific prescription and frame) are especially well-paired with high index materials because the digital optimization can partially compensate for the lower Abbe value.
Summary: Choosing the Right Lens Index
The right lens index is a balance of three factors:
- Prescription strength: The primary driver. Use the tables above as a guide.
- Frame style: Rimless and semi-rimless frames need higher indexes. Larger frames increase effective thickness.
- Budget: 1.61 offers the best balance of thinness, optical quality, and cost for most people who do not qualify for 1.50.
When in doubt, ask your optician. They can calculate the approximate edge thickness for any combination of prescription, index, and frame size — and advise whether a higher index is genuinely worth the upgrade for your specific situation.