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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.
A corrective lens is a device that improves visual perception by correcting refractive errors. Learn about the different types of corrective lenses, such as glasses, contact lenses, intraocular lenses, and their prescriptions, uses, and advantages.
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.
Learn about the different types of optical prisms, such as dispersive, reflective, beam-splitting and polarizing prisms, and how they refract, reflect or split light. Find out how prisms are made of transparent materials like glass, acrylic or fluorite, and how they can create spectra, images or polarizations.
Adjustable focus eyeglasses have one focal length, but it is variable without having to change where one is looking. Possible uses for such glasses are to provide inexpensive eyeglasses for people from low-income groups , developing countries , third world countries or to accommodate for presbyopia.
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.
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