OCT 08

High Index Lenses Disadvantages

The benefits of high index lenses are hard to overlook. Due to the chemical makeup of the material from which they are created, high index lenses have more refractive power than standard plastic or glass. This means that stronger prescriptions are lighter and thinner when formed from high index material. And when the subject is eyeglasses, weight and thickness can mean a lot.

So What Are the Disadvantages of High Index Lenses?

  1. Higher Cost
  2. Abbe Value (or Distortion Factor)
  3. More Brittle (in Glass Form)
  4. Negligible Benefit (in Some Instances)
  5. More Reflective

1. Higher Cost
High index lenses, whether in glass or plastic form, are noticeably more expensive than traditional plastic or glass lenses. Even within the high index spectrum, prices range dramatically; a 1.90 high index lens, for example, is about three times the cost of a 1.67 high index lens. The expense is primarily due to the added cost of the manufacturing process which, of course, is passed along to consumers.

2. Abbe Value
The “Abbe Value” is a measurement of lens distortion. It’s named after German physicist and mathematician Ernst Abbe, who discovered that different materials yield different levels of chromic aberration. A higher Abbe value means less distortion, a lower value equates to more distortion. 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.

3. More Brittle
1.74 high index and above is only available in glass, and high index glass lenses are relatively brittle. If one is not a careful handler of glasses – you know who you are! – glass high index lenses are probably not the best choice.

4. Negligible Benefit
The positive qualities of high index lenses apply to a large group of corrective eye-wear consumers but not to all. If your prescription is a relatively weak one, the weight and thickness variations between standard lenses and high index lenses would not vary all that much. If high index lenses cannot offer you a noticeable reduction in weight or increase in appearance, they may not be worth the higher cost to you.

5. More Reflective
High index lenses reflect a considerably higher percentage of light than standard lenses. This problem can easily be remedied with the application of an anti-glare coating, but it’s another factor to bear in mind when weighing the pros and cons of high index lenses.

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