1.67 high index lenses are a type of prescription eyeglass lens made from a material that bends light more efficiently than standard plastic, resulting in lenses that are roughly 25% thinner and up to 30% lighter. They’re one of the most popular upgrades for people with moderate to strong prescriptions who want glasses that don’t look thick or feel heavy on their face.
How the Refractive Index Works
Every lens material has a refractive index, a number that describes how effectively it bends light. Standard plastic lenses (called CR-39) have a refractive index of 1.50. The higher the number goes, the less material is needed to achieve the same corrective power. High index lenses range from 1.53 to 1.74, with 1.67 sitting near the top of that range.
A 1.67 lens does the same job as a standard 1.50 lens. It corrects your vision identically. The difference is purely physical: because the material bends light more efficiently, the lens can be ground thinner, especially at the edges for nearsighted prescriptions or at the center for farsighted ones. That reduction in bulk also cuts weight. The density of 1.67 material is about 1.42 grams per cubic centimeter compared to 1.32 for standard plastic, but because the lens itself is so much thinner, a finished 1.67 lens ends up roughly 25 to 30% lighter overall.
Who Benefits Most From 1.67 Lenses
The stronger your prescription, the more difference you’ll notice. In standard plastic, strong prescriptions produce thick, heavy lenses with noticeable edge bulge. 1.67 lenses are generally recommended for prescriptions in the range of +/-7.00 to +/-9.00 for sphere correction and +/-3.25 to +/-4.00 for astigmatism correction. If your prescription falls below about +/-4.00, a 1.60 index lens may give you enough thinning at a lower cost, and you won’t see a dramatic visual difference by going higher. If your prescription is above +/-9.00, you might benefit from stepping up to 1.74, the thinnest option available.
Frame choice also matters. If you prefer large frames, thinner lenses become more important because lens thickness increases toward the edges. People who want lightweight, comfortable glasses for all-day wear also tend to appreciate the weight reduction, even at moderate prescriptions.
1.67 vs. 1.74: Is the Upgrade Worth It?
This is one of the most common questions people have when shopping for high index lenses. The honest answer: the physical difference is small. In most frames, the thickness difference between 1.67 and 1.74 is less than half a millimeter. Unless you have a very strong prescription or are using a rimless frame where the lens edge is fully exposed, the visual difference is hard to spot.
Where you will notice a difference is in price. 1.74 lenses typically cost around $100 more than 1.67 lenses. On the optical quality side, 1.67 actually has a slight advantage: it produces less chromatic aberration (color fringing), which means marginally clearer vision at the edges of your lenses. For most people, 1.67 hits the sweet spot between thinness, weight, optical quality, and cost.
Optical Clarity and Color Fringing
One tradeoff with any high index material is a property measured by something called the Abbe value. This number describes how much a lens splits white light into its component colors, similar to a prism effect. Standard plastic has an Abbe value around 58. The 1.67 material has an Abbe value of about 33, which is noticeably lower.
In practice, this means you may see slight color fringing at the edges of objects, particularly in your peripheral vision. It looks like thin rainbow outlines along high-contrast edges. Most people with moderate prescriptions don’t find this bothersome, especially once they’ve worn the lenses for a few days and their brain adjusts. But if you’re particularly sensitive to visual distortions, or if your prescription is very strong, it’s worth knowing about. The effect is more pronounced at higher prescriptions because the lens curvature is more extreme toward the periphery.
Why Anti-Reflective Coating Matters
High index materials reflect more light than standard plastic. This is a direct consequence of the physics: the more a material bends light, the more light bounces off its surface instead of passing through. Without an anti-reflective coating, 1.67 lenses create several problems. Other people see bright reflections instead of your eyes. The reflected light bouncing around inside the lens reduces your visual clarity. Glare from oncoming headlights or overhead lighting becomes more intense, potentially causing discomfort, headaches, and eye fatigue. The increased surface reflection can also bounce more UV light into your eyes from behind.
For all of these reasons, anti-reflective coating is essentially non-negotiable with 1.67 lenses. Most optical shops include it automatically when you order high index, and online retailers almost always bundle it in. If you’re quoted a price for 1.67 lenses without anti-reflective coating, that’s a red flag.
Cost and Where to Buy
Pricing for 1.67 lenses varies widely depending on where you buy. At a brick-and-mortar optical shop, upgrading to 1.67 from standard plastic typically adds $100 to $250 to the cost of your lenses, depending on the brand and included coatings. Online retailers sell 1.67 lenses for significantly less, sometimes as low as $40 for the lens upgrade alone, though the total price depends on your prescription complexity and any additional coatings like blue light filtering or photochromic tinting.
If you’re buying through vision insurance, check whether your plan covers high index lenses or offers a discount. Many plans cover standard plastic and require you to pay the difference out of pocket for a high index upgrade. Even so, the $50 to $150 premium over standard lenses is often the single most noticeable upgrade you can make to your everyday glasses, particularly if you’ve been wearing thick, heavy lenses and didn’t realize a thinner option existed.
Durability Considerations
High index plastics are not as inherently impact-resistant as polycarbonate, a material commonly used in safety glasses and children’s eyewear. Research from the University of Waterloo testing ballistic impact resistance found that 1.67 lenses at a standard 2.0 mm center thickness withstood impacts at about 40 meters per second, with thicker versions performing better. For everyday wear, this level of durability is perfectly adequate. But if you need safety-rated eyewear or glasses for sports, polycarbonate or Trivex are better choices regardless of prescription strength.
1.67 lenses scratch at roughly the same rate as other plastic lens materials, so a scratch-resistant coating (usually included with anti-reflective coating) is a worthwhile addition. The material is also compatible with most frame types, including rimless and semi-rimless designs, though your optician may recommend a slightly thicker minimum edge to ensure the lens holds up where the drill holes or grooves are placed.