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2. Prism correction - Wikipedia

   en.wikipedia.org/wiki/Prism_correction

   Prism dioptres. Prism correction is commonly specified in prism dioptres, a unit of angular measurement that is loosely related to the dioptre. Prism dioptres are represented by the Greek symbol delta (Δ) in superscript. A prism of power 1 Δ would produce 1 unit of displacement for an object held 100 units from the prism. [2]

3. Zenni Optical - Wikipedia

   en.wikipedia.org/wiki/Zenni_Optical

   www .zennioptical .com. Zenni Optical (formerly 19dollareyeglasses.com) is an American online retailer of prescription glasses and sunglasses. Founded in 2003 by Tibor Laczay and Julia Zhen, it is based in Novato, California . The company sells more than 2,000 types of prescription glasses and sunglasses as well as 45 types of contact lenses.

4. History of optics - Wikipedia

   en.wikipedia.org/wiki/History_of_optics

   History of optics. Modern ophthalmic lens making machine. Optics began with the development of lenses by the ancient Egyptians and Mesopotamians, followed by theories on light and vision developed by ancient Greek philosophers, and the development of geometrical optics in the Greco-Roman world. The word optics is derived from the Greek term ...

5. 10 Great Sites to Buy Cheap Eyeglasses Online - AOL

   www.aol.com/10-great-sites-buy-cheap-140036394.html

   Warby usually takes five to 10 business days to ship your order, with home try-ons arriving in about five days. 2. Zenni Optical. Probably one of the cheapest online eyewear stores out there ...

6. Crown glass (optics) - Wikipedia

   en.wikipedia.org/wiki/Crown_glass_(optics)

   Crown glass is a type of optical glass used in lenses and other optical components. It has relatively low refractive index (≈1.52) and low dispersion (with Abbe numbers between 50 and 85). Crown glass is produced from alkali-lime silicates containing approximately 10% potassium oxide and is one of the earliest low dispersion glasses .

7. Bifocals - Wikipedia

   en.wikipedia.org/wiki/Bifocals

   Bifocals. A bifocal lens with areas of differing magnification. Bifocals with separate lenses. In this case, the Swedish ethnologist Jan-Öjvind Swahn [ sv]. Bifocals are eyeglasses with two distinct optical powers. Bifocals are commonly prescribed to people with presbyopia who also require a correction for myopia, hyperopia, and/or astigmatism .