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Zenni Optical is an American company that sells prescription glasses, sunglasses, and contact lenses online. Founded in 2003, it has over 1,000 employees in China and the US, and offers low prices, diverse options, and themed glasses.
Bifocals are eyeglasses with two distinct optical powers, commonly prescribed to people with presbyopia. Benjamin Franklin is generally credited with the invention of bifocals, but there is some evidence that others may have come before him.
Learn how to interpret and write an eyeglass prescription that includes sphere, cylinder and axis components. Sphere and cylinder specify the power of the lenses, and axis defines the orientation of the cylinder relative to horizontal and vertical.
Prentice's rule is a formula to calculate the amount of prism correction in a lens based on decentration and lens power. It can be used for prescribing, tolerance control, or determining unprescribed prism in eyeglasses.
Unlike with bifocals, near-vision correction is achieved over the entire field of view, in any direction.Distance vision corrections are made by re-adjusting the lens for distance, instead of by tilting and/or rotating the head to view object through the best part of the lens for the distance.
Learn about glasses, also known as eyeglasses and spectacles, which are vision eyewear with clear or tinted lenses mounted in a frame. Find out about corrective, safety, sunglasses and other types of glasses, as well as their history and evolution.
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