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  2. Prism correction - Wikipedia

    en.wikipedia.org/wiki/Prism_correction

    Prism dioptres. Prism correction is commonly specified in prism dioptres, a unit of angular measurement that is loosely related to the dioptre. Prism dioptres are represented by the Greek symbol delta (Δ) in superscript. A prism of power 1 Δ would produce 1 unit of displacement for an object held 100 units from the prism. [2]

  3. Vertex distance - Wikipedia

    en.wikipedia.org/wiki/Vertex_distance

    Vertex distance. Vertex distance. Vertex distance is the distance between the back surface of a corrective lens, i.e. glasses (spectacles) or contact lenses, and the front of the cornea. Increasing or decreasing the vertex distance changes the optical properties of the system, by moving the focal point forward or backward, effectively changing ...

  4. Autorefractor - Wikipedia

    en.wikipedia.org/wiki/Autorefractor

    The majority of autorefractors calculate the vision correction a patient needs (refraction) by using sensors that detect the reflections from a cone of infrared light. These reflections are used to determine the size and shape of a ring in the retina which is located in the posterior part of the eye.

  5. Optical contact bonding - Wikipedia

    en.wikipedia.org/wiki/Optical_contact_bonding

    Optical contact bonding. Gauge blocks wrung together and held horizontally. The blocks are held together solely by the adhesion of their extremely flat surfaces, which is so strong that it easily supports their weight. Optical contact bonding is a glueless process whereby two closely conformal surfaces are joined, being held purely by ...

  6. Refractometer - Wikipedia

    en.wikipedia.org/wiki/Refractometer

    The refractometer is used to help identify gem materials by measuring their refractive index, one of the principal properties used in determining the type of a gemstone. Due to the dependence of the refractive index on the wavelength of the light used ( i.e. dispersion ), the measurement is normally taken at the wavelength of the sodium line D ...

  7. Contact lens - Wikipedia

    en.wikipedia.org/wiki/Contact_lens

    Contact lenses are ocular prosthetic devices used by over 150 million people worldwide, and they can be worn to correct vision or for cosmetic or therapeutic reasons. In 2010, the worldwide market for contact lenses was estimated at $6.1 billion, while the US soft lens market was estimated at $2.1 billion. [3]

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