Difference between revisions of Severe myopia
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===Opt for lenses with a high refractive index=== | ===Opt for lenses with a high refractive index=== | ||
The higher the [https://en.wikipedia.org/wiki/Refractive_index refractive index] (''n''), the smaller the difference in front-back curvature needs to be for a lens to reach a given minus strength. Opting for high-''n'' glass reduces the thickness of the lens edges and lowers the volume of the glass in the lens. This reduces weight, but less so than the volume reduction because the high refractive index is achieved by admixing lead in the glass[https://en.wikipedia.org/wiki/Lead_glass]: | The higher the [https://en.wikipedia.org/wiki/Refractive_index refractive index] (''n''), the smaller the difference in front-back curvature needs to be for a lens to reach a given minus strength. Opting for high-''n'' glass therefore reduces the thickness of the lens edges and thereby significantly lowers the volume of the glass in the lens. This reduces weight, but less so than the volume reduction because the high refractive index is achieved by admixing lead in the glass[https://en.wikipedia.org/wiki/Lead_glass]: leaded glass weight more per unit volume. | ||
There are disadvantages: | There are disadvantages: | ||