Prism Thinning Essay

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Prism-Thinning Progressive lenses give the wearer the closest thing to natural vision. Having no visible line identifying the lens as multifocal is an appealing cosmetic benefit, in order to ensure that the spectacle wearers enjoy the superior cosmetics that they expect with their progressive lenses, the thickness and weight of these lenses has to be significantly minimized using a technique known as prism-thinning. Prism-thinning (also called equi-thinning) is the process of grinding vertical prism into a progressive lens blank in order to minimize the thickness difference between the top and bottom edges of the lens as well as to reduce the overall thickness of the lens. Most commonly, prism-thinning involves grinding base down prism into a progressive lens. In some cases base up prism may be appropriate. Although base down prism is added to the lens, the real objective is to remove base up prism from the lens to eliminate the excess thickness from the upper edge of the lens blank. In addition it balances the thickness difference between the top and bottom of the lens blank. Also, reduces the center thickness of progressive lenses with high hyperopic prescriptions or high addition powers. This overall reduction in lens thickness also makes the lens lighter in weight. This procedure offers two important benefits to the spectacle wearer. First, thinner lenses with more consistent edge profile that offers better cosmetics and second, lighter-weight lenses that are more comfortable to wear. In order to avoid creating a vertical prismatic imbalance, equal vertical prism is ground into both lenses with the same magnitude and

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