Pros and Cons for High Index Lenses
By their very nature and chemical makeup, high index lenses have distinct advantages over standard plastic or glass.
High Index Lenses: Pros and Cons
This does not mean, however, that high index lenses are without drawbacks. Today we’ll examine both the pros and cons of high index lenses and hopefully give you a better idea of whether or not they’re right for you.
High Index Material Advantages:
- Higher index results in less use of material
- Lighter than standard plastic or glass
- Thinner than standard plastic or glass
- Reduced edge size
- Allows for multiple single- and progressive-use designs
The first advantage on this list leads to many of the others, and gives high index lenses their name. The measurement of an index describes how much light is refracted, or bent, through the material. The higher the index rating, the less material required to make a lens in a particular prescription. And in the eye-wear world, less material is a huge advantage.
Because high index lenses can form prescriptions using less physical material, they provide lenses that are both lighter and thinner than identical lenses formed out of standard glass or plastic. If you have a very slight corrective prescription, you might not enjoy much of a boost here; however, the stronger your prescription gets, the more benefit you’ll receive. Lens that would be extremely thick and heavy if made of standard material can be considerably thinner and lighter if formed of high index material.
Reduced edge size also relates to the thinness of the high index lens. A thick standard glass or plastic lens will have edges that stick out from behind your frames. You may also require thicker, fuller frames to both support and disguise the exposed edges – thereby limiting your frame choices to styles you may not particularly enjoy. Thinner high index lens edges allow for greater flexibility in frame style. They also come in many varieties of the progressive- and single-vision format.
High Index Material Disadvantages
- Higher cost
- Abbe value
- More brittle and reflective
Perhaps the most obvious disadvantage is the higher cost of high index lenses, which can be significant. For example, a 1.90 high index lens (the highest “high index” rating available) costs about three times the amount of a 1.67 high index lens (the lowest “high index” rating available). The expense is due to the added cost of the manufacturing process and material waste that is associated with the more exacting process of forming, grinding, and finishing high index prescriptions. Not surprisingly, much of this added expense is passed along to you, the consumer.
Abbe value, which is a measurement of lens distortion, is also increased in high index lenses. High index lenses have a lower Abbe rating than identical prescriptions formed from standard material. So while the thinner, lighter high indexes offer cosmetic benefits, they do not surpass traditional lenses in vision quality.
Finally, high index lenses can be more brittle and are definitely more reflective than standard materials. 1.74 high index and above is only available in glass, and high index glass lenses are more brittle and easier to break than plastic. High index lenses also reflect a higher percentage of light than standard lenses. Because of this, an anti-glare coating is strongly recommended with the purchase of high index lenses.