Most people are aware that a higher prescription typically means thicker lenses. If you need a strong prescription to see clearly, you would have no choice but to wear thicker lenses, but that was before. Lens technology has evolved a lot in recent years and now, even those who require higher prescriptions can still wear thinner lenses, which are much lighter and more comfortable. All that’s needed is to choose a better lens index.
What Is Lens Index?
The lens index is a range of numbers that denote the thickness of a lens, with the number being inversely proportional to the thickness. That is, the higher the lens index number, the thinner the lens.
As prescription strength gets higher, the lenses have a tendency to become a lot thicker. To save people from the burden of wearing cumbersome eyeglasses, a higher lens index is usually applied to stronger prescriptions. This keeps the lens relatively thin despite the high prescription.
Common Types of Eyeglasses Lens Index
The lens index number for eyeglasses ranges from 1.5, which is the thickness of all standard or regular lenses, all the way to 1.9, which are the thinnest lenses available today. Of these numbers, there are four that stand out as they are the most commonly chosen by wearers of eyeglasses.
1.56 - Standard Index Lenses
Notably thinner and lighter than standard lenses, these are suitable for SPH +4.00, -4.00 prescriptions. These lenses are about 15% thinner than ordinary lenses and can be fitted into any kind of frame.
1.61 - Thin Lenses
Popularly known as super thin lenses, the 1.61 lenses are a popular choice among people who have a prescription strength from SPH +3.00, -+3.00 up to +6.00, -6.00, or even higher. These lenses are approximately 20% thinner than the standard 1.5 index, and are best for full-rim and semi-rim frames.
1.67 - Super Thin Lenses
For much stronger prescriptions like those that range from +6.25, -6.25 to +8.00, -8.00, eye doctors usually recommend the 1.67 lens index ultra-thin lenses. They are also suitable for correcting astigmatism from +3.25, -3.25 to +4.00, -4.00.
1.74 - Thinnest and Lightest Lenses
These high-index lenses are the thinnest and lightest lenses that are easily available from most optical shops and eyewear manufacturers. 1.74 lenses are so thin and lightweight that the wearer would barely feel the weight of the glasses.
Besides these popular types, there are also the 1.8 and 1.9 lenses, which are even thinner and lighter. These two varieties are reserved only for very strong prescriptions and are made of extremely thin glass material.
Why Are High Index Lenses More Expensive?
The higher the lens index, the more expensive it costs. Why is this so? Regular lenses are made of a plastic material called CR-39, and are the most affordable material for eyeglass lenses. However, this material is not capable of achieving the thinness of the high index lenses.
To produce high index lenses that are much thinner and lighter, manufacturers use a different kind of plastic material with more light bending capacity. These materials cost significantly more than the regular CR-39. Many users feel that the cost is worth it because, in addition to being thinner and lighter, high-index lenses are also more flattering to wear.
How to Choose the Right Lens Index?
The first criterion to consider in order to choose the right lens index is your prescription. As you can see from above, the various lens indexes are suitable for a specific range of prescription strength. While getting checked, you can ask your eye doctor what they think should be the appropriate lens index for your particular prescription.
For most prescriptions, people actually have no problem wearing glasses with a 1.5 lens index, particularly if their prescriptions are not that high anyway. Some don't even mind the thick lenses as the prescription gets higher. But if you want to wear a thinner and more comfortable lens, then high-index lenses are a great option.
Take note that the higher index lenses might not work for certain frame types, like rimless or semi-rimmed glasses. Very thin lenses can be extremely delicate and must only be fitted into full-rim glasses for safety.