1.80 High Index Glass Lenses
“Index.” You may have run into the term while shopping for glasses online or at the optometrist’s office. You may have heard your number referred to as a “high index.” So what exactly is the index, and how does it relate to your prescription?
High Index Glass Lenses: 1.80
Let’s start with the fact that corrective lenses work by refracting, or bending, incoming light waves. To do this, they are shaped into a particular curve; whatever curve your eye needs to best improve your vision. The index is simply the measure of this curve. Therefore, it is the term that identifies your particular prescription and dictates the degree to which your lenses will be ground.
Your index requirements are determined when you have your eye examination. The higher the index number, the smaller the curvature. And a smaller curve requires less overall lens material. So, the higher your index number, the thinner your lens can be.
Anything over 1.60 is considered “high index.” The highest index lens – and therefore the thinnest – is a 1.90. Today we’re examining 1.80 high index lenses, and here’s where the material your lens is made of comes into play. Plastic only goes as high as 1.74 index – so 1.80 lenses are only available in glass.
To make them, technicians start with a titanium-based glass. This material is best suited for producing the curve required for a 1.80 index. To achieve this curve, the glass is ground to 2.0mm thick at the center.
The biggest “knock” against glass lenses is their weight; they are typically at least twice as heavy as a plastic or polycarbonate lens. But having a higher index means you’ll need less material to obtain your ideal prescription. And glass also has certain properties that make it an excellent choice for eyewear. These include:
- Superior optical quality.
- Excellent scratch resistance, so much so that no scratch-resistant coating is required.
- Anti-reflective coatings adhere particularly well to glass lenses.
- Is often less expensive than comparable plastics or polycarbonates.
- Cleaner, less noticeable edge when used for bifocals or trifocals.
- Naturally more resistant to chemicals.
- Changes very little over time and will not yellow over the course of its lifespan.
So if you require a 1.80 index or other high index, don’t be put off by the fact that your lenses are only available in glass. It’s not necessarily a limitation. You’re simply exchanging certain benefits for others…and the benefits of glass may work particularly well for you.