The Complete High-Index Lens Guide: 1.50 vs. 1.60 vs. 1.67 vs. 1.74 Profiles

In materials science, the refractive index (n) describes how efficiently a transparent substance slows down and bends light waves compared to a vacuum (where n = 1.000). Water has an index of 1.333; crown glass has an index of 1.523.

In ophthalmic lens manufacturing, a higher index number means the material bends light more aggressively. Because light bends more sharply upon entering the material, less curvature and physical material are required to achieve the exact same dioptric prescription. A higher index directly translates into a thinner, flatter, and lighter lens.

Ophthalmic lenses are universally manufactured across four standard index tiers:

• 1.50 Standard Index (CR-39 Monomer): The baseline optical polymer invented by Columbia Resins in 1940. Offers the highest optical clarity (Abbe value 58), but is the thickest and heaviest profile. Ideal for mild prescriptions between Plano (0.00) and ±2.00D.
• 1.60 High-Index (MR-8 Polymer): Up to 20% thinner and 25% lighter than standard CR-39. Excellent tensile strength, making it the required choice for semi-rimless and drill-mount rimless frames. Ideal for prescriptions from ±2.00D to ±4.00D.
• 1.67 Ultra-Thin High-Index (MR-7 / MR-10): Up to 35% thinner than 1.50 lenses. Drastically reduces edge thickness in high negative prescriptions (-4.00D to -7.00D), preventing unsightly edge protrusion from stylish metal and acetate frames.
• 1.74 Ultra-High Index: The thinnest plastic optical substrate commercially available. Up to 50% thinner than standard lenses. Engineered specifically for severe prescriptions (-7.00D and above or +5.00D and above), eliminating the 'bug-eye' magnification effect in plus lenses and the 'minified eye' effect in strong minus lenses.

In optical physics, you never get something for nothing. As the refractive index of a polymer increases, its Abbe value decreases. Named after German physicist Ernst Abbe, the Abbe number measures how much a material disperses white light into its component rainbow colors (chromatic aberration).

A material with a high Abbe value (like CR-39 at 58 or MR-8 1.60 at 41) has almost zero color fringing. A material with a low Abbe value (like polycarbonate at 30 or 1.74 index at 33) can introduce subtle yellow-blue color fringes when looking through the extreme periphery of the lens. That is why 1.60 index (MR-8) is universally recognized by optometrists as the sweet spot—delivering exceptional thinness while preserving crystal-clear Abbe clarity.