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2. Astigmatism (optical systems) - Wikipedia

   en.wikipedia.org/wiki/Astigmatism_(optical_systems)

   Astigmatism (optical systems) An optical system with astigmatism is one where rays that propagate in two perpendicular planes have different foci. If an optical system with astigmatism is used to form an image of a cross, the vertical and horizontal lines will be in sharp focus at two different distances. The term comes from the Greek α- (a ...

3. Progressive lens - Wikipedia

   en.wikipedia.org/wiki/Progressive_lens

   Progressive lenses are corrective lenses used in eyeglasses to correct presbyopia and other disorders of accommodation. They are characterised by a gradient of increasing lens power, added to the wearer's correction for the other refractive errors. The gradient starts at the wearer's distance prescription at the top of the lens and reaches a ...

4. Visual acuity - Wikipedia

   en.wikipedia.org/wiki/Visual_acuity

   Eye examination for visual acuity. Visual acuity is a measure of the spatial resolution of the visual processing system. VA, as it is sometimes referred to by optical professionals, is tested by requiring the person whose vision is being tested to identify so-called optotypes – stylized letters, Landolt rings, pediatric symbols, symbols for the illiterate, standardized Cyrillic letters in ...

5. Eyeglass prescription - Wikipedia

   en.wikipedia.org/wiki/Eyeglass_prescription

   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.

6. Pentax (lens) - Wikipedia

   en.wikipedia.org/wiki/Pentax_(lens)

   1995: Pentax introduces the world’s first fish-eye zoom lens. That lenses was the F 17-28mm F3.5-4.5 Fish-eye Zoom. [1] 2000: Pentax develops and commercializes the world's first diffractive DVD/CD-compatible hybrid pickup lens. [1] 2009: Pentax introduces the world’s first autofocus fisheye lens. That lens is the DA 10-17mm ED (IF) Fish ...

7. Adjustable-focus eyeglasses - Wikipedia

   en.wikipedia.org/wiki/Adjustable-focus_eyeglasses

   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 ...