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A Fresnel lens (/ ˈ f r eɪ n ɛ l,-n əl / FRAY-nel, -nəl; / ˈ f r ɛ n ɛ l,-əl / FREN-el, -əl; or / f r eɪ ˈ n ɛ l / fray-NEL [1]) is a type of composite compact lens which reduces the amount of material required compared to a conventional lens by dividing the lens into a set of concentric annular sections.
Schachar—Ronald A. Schachar has proposed in 1992 what has been called a "rather bizarre geometric theory" [36] which claims that focus by the human lens is associated with increased tension on the lens via the equatorial zonules; that when the ciliary muscle contracts, equatorial zonular tension is increased, causing the central surfaces of ...
Adjustable focus lenses, like single-focus lenses, also reduce image-jump and spatial distortion in the field of view associated with traditional multi-focal lenses. Additionally, the ideal near-vision correction can be achieved with precision, because the variable lenses emulate the focusing action of the youthful (non-presbyopic) eye.
An Intraocular lens (IOL) is a lens implanted in the eye usually as part of a treatment for cataracts or for correcting other vision problems such as short sightedness and long sightedness; a form of refractive surgery. If the natural lens is left in the eye, the IOL is known as phakic, otherwise it is a pseudophakic lens (or false
Some dental loupes are flip-type, which take the form of two small cylinders, one in front of each lens of the glasses. Other types are inset within the lens of the glasses. Dental caries, also known as cavities, are most accurately identified by visual and tactile examination of a clean, dry tooth. [9]
Objects resembling lenses date back 4000 years although it is unknown if they were used for their optical properties or just as decoration. [6] Greek accounts of the optical properties of water-filled spheres (5th century BC) were followed by many centuries of writings on optics, including Ptolemy (2nd century) in his Optics, who wrote about the properties of light including reflection ...
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