MICHAEL / Eyewear Answers & Calculators
Do I need 1.61, 1.67, or 1.74 high-index lenses for my prescription?
Direct answer:For prescriptions within ±3.00 D, 1.56 (US$10/pair) or 1.61 (US$15/pair) is already slim; between ±4.00 D and ±6.50 D, 1.67 Thin High-Index (US$55/pair Single Vision) delivers the best thickness-to-price value; upgrade to 1.74 Ultra High-Index (US$100/pair Single Vision) when your power exceeds ±6.50 D (supported down to -20.00 / +16.00 D), and pair strong powers with a 40–44 mm frame.
Side-by-Side Comparison: 1.56, 1.61, 1.61 Pro, 1.67 and 1.74
Refractive index measures how efficiently the lens resin bends light. Higher numbers use less material at the outer edge (for minus nearsighted prescriptions) or center (for plus farsighted prescriptions):
| Refractive Index | Recommended Power | Max Supported SPH Range | Single Vision Clear Pair | Progressive Clear Pair |
|---|---|---|---|---|
| 1.56 Standard | 0.00 to ±3.00 D | -8.00 to +6.00 D (SV) | US$10 (US$5 + US$5) | US$60 (US$35 + US$25) |
| 1.61 High-Index | ±2.00 to ±4.50 D | -10.00 to +8.00 D (SV) | US$15 (US$5 + US$10) | US$65 (US$35 + US$30) |
| 1.61 Pro Extra-Hardened | ±2.00 to ±5.00 D | -10.00 to +8.00 D (SV) | US$30 (US$5 + US$25) | US$80 (US$35 + US$45) |
| 1.67 Thin High-Index | ±4.00 to ±6.75 D | -12.00 to +9.00 D (SV) | US$55 (US$5 + US$50) | US$95 (US$35 + US$60) |
| 1.74 Ultra High-Index | ±6.50 D and stronger | -20.00 to +16.00 D (SV Clear) | US$100 (US$5 + US$95) | US$144 (US$35 + US$109) |
Why Frame Width Matters Just as Much as 1.67 vs. 1.74
On concave nearsighted (-) lenses, edge thickness grows rapidly with lens diameter. Putting a -6.00 D 1.67 lens into a compact 42 mm round full-rim acetate frame often produces a cleaner, thinner edge than putting a pricier 1.74 lens into an oversized 54 mm wire frame. Full-rim cellulose acetate eyewires (~4 mm thick) also conceal most of the bevelled edge from side view.
Follow-Up Questions Buyers Ask
Is 1.74 worth the US$45 upgrade over 1.67 for a -4.50 D prescription?
Usually no. Around -4.00 D to -5.50 D, 1.67 Thin High-Index (US$55/pair in Single Vision Clear) already removes most visible edge bulk, while 1.74 (US$100/pair) shaves off roughly an extra fraction of a millimetre. Save 1.74 for powers past ±6.50 D or wider frame choices.
Do 1.67 and 1.74 high-index lenses come with anti-reflective coating included?
Yes. High-index resins reflect slightly more surface light when uncoated, which is why every MICHAEL 1.61, 1.67 and 1.74 package includes our standard green anti-reflective and scratch-resistant base coating at US$0 extra.
Can I order 1.74 lenses in Polarized Sunglasses or Standard All-Day Progressives?
Under our confirmed lens schedule, 1.74 Ultra High-Index is available on Single Vision and Upgrade/Advanced Progressive packages in Clear, Blue-Light, Photochromic and Photochromic + Blue-Light. Colored Sun, Polarized, Standard-tier Progressive and Office Progressive packages top out at 1.67 Thin High-Index.
Clinical & Regulatory References
- Nearsightedness (Myopia): Dioptre Strength & Corrective Lenses ↗ (NIH National Eye Institute (NEI)) Covers myopia dioptre progression and why stronger concave prescriptions require higher-refractive-index materials.
- 21 CFR § 801.410: Impact-Resistant Ophthalmic Lenses Regulation ↗ (U.S. Food & Drug Administration (eCFR)) Establishes federal impact-resistance standards for consumer prescription optical resin lenses.