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A prescription of −1.00 +0.25 × 180 describes a lens that has a horizontal power of −1.00 D and a vertical power of −0.75 D. Only ophthalmologists write prescriptions in + cylinder. An optometrist would write a prescription in - (minus) cylinder. All spectacle and contact lenses would be made in minus cylinder.
With the photochromic material dispersed in the glass substrate, the degree of darkening depends on the thickness of glass, which poses problems with variable-thickness lenses in prescription glasses. With plastic lenses, the material is typically embedded into the surface layer of the plastic in a uniform thickness of up to 150 μm.
Transitions Optical is a U.S.-based company known for manufacturing photochromic lenses, which darken on exposure to specific types of light. The company was founded in 1990. [1] In 1991, Transitions Optical became the first company to commercialize and manufacture plastic photochromic lenses. [2]
The gradient starts at the wearer's distance prescription at the top of the lens and reaches a maximum addition power, or the full reading addition, at the bottom of the lens. The length of the progressive power gradient on the lens surface depends on the design of the lens, with a final addition power between 0.75 and 3.50 dioptres.
Reading glasses are single vision lenses designed for near work and include over the counter glasses. They come in two main styles: full frames, in which the entire lens is made in the reading prescription, and half-eyes, style glasses that sit lower down on the nose. [2]
The post This Is What Those Numbers on Your Glasses Mean appeared first on Reader's Digest. The numbers on your eyewear are more important than you think—an optometrist tells us why. The post ...
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