The Disadvantages of a High Index Lens

Written by nelly morrison
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The Disadvantages of a High Index Lens
High index lenses are thinner and lighter. (BananaStock/BananaStock/Getty Images)

High index lenses are made from special glass or plastic that refracts light in a different way from conventional lenses. The stronger the prescription, the more refractive ability the lens must have. Generally this makes prescription lenses very thick. High index lenses have more refractive power so they do not have to be as thick. These types of lenses are thinner and lighter than conventional lenses; however, high index lenses do come with a downside.

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Suitability

According to "Eyecare Professional Magazine," with some prescriptions, there would be little or no advantage in having a high index lens, because the weight and thickness benefits between a high index lens and a conventional lens would be minimal. It's important to choose the material of high index lenses according to need. High index lenses made from glass are very brittle and not suitable for children or people involved in sports.

Abbe Value

Ernst Abbe was a German mathematician and physicist who discovered that lenses made from different materials have varying amounts of chromatic aberration. This is called the Abbe value: the higher the Abbe value, the least amount of distortion when looking through the lens. Standard glass lenses have a high Abbe value, but high index lenses have a lower Abbe value. Cosmetically high index lenses may be more attractive, but they do not correct vision as well as standard lenses.

Antireflective Coating

Conventional lenses reflect 8 per cent of light, while high index lenses reflect up to 50 per cent of light. This high percentage can lead to eye fatigue and make night driving difficult. With an antireflective coating, you can solve this problem. Keep in mind that antireflective coatings can deteriorate with everyday wear and tear.

Cost

High index lenses cost more to manufacture because they have more refractive ability. High index lenses can also be made from polycarbonate. Polycarbonate is tougher and ideal for children and sports enthusiasts; however, the material has a low Abbe value and costs more. Another option is Trivex, developed in 2001. It is very tough, but comes with a significantly higher price tag than conventional lenses.

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