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Eyeglass prescription. Using a phoropter to determine a prescription for eyeglasses. An eyeglass prescription is an order written by an eyewear prescriber, such as an optometrist, that specifies the value of all parameters the prescriber has deemed necessary to construct and/or dispense corrective lenses appropriate for a patient.
Corrective lenses are typically prescribed by an ophthalmologist or an optometrist. The prescription consists of all the specifications necessary to make the lens. Prescriptions typically include the power specifications of each lens (for each eye). Strengths are generally prescribed in quarter- diopter steps (0.25 D) because most people cannot generally distinguish between smaller increments ...
Prism correction is measured in prism dioptres. A prescription that specifies prism correction will also specify the "base". The base is the thickest part of the lens and is opposite from the apex. Light will be bent towards the base and the image will be shifted towards the apex. In an eyeglass prescription, the base is typically specified as up, down, in, or out, but left and right are also ...
Vertex distance is important when converting between contact lens and glasses prescriptions and becomes significant if the glasses prescription is beyond ±4.00 diopters (often abbreviated D). The formula for vertex correction is , where F c is the power corrected for vertex distance, F is the original lens power, and x is the change in vertex distance in meters.
A lensis a transmissive opticaldevice that focuses or disperses a light beamby means of refraction. A simple lensconsists of a single piece of transparent material, while a compound lensconsists of several simple lenses (elements), usually arranged along a common axis. Lenses are made from materials such as glassor plasticand are ground, polished, or moldedto the required shape. A lens can ...
Adjustable focus eyeglasses are eyeglasses with an adjustable focal length. They compensate for refractive errors (such as presbyopia) by providing variable focusing, allowing users to adjust them for desired distance or prescription, or both. Current bifocals and progressive lenses are static, in that the user has to change their eye position ...
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