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  2. PRISM - Wikipedia

    en.wikipedia.org/wiki/PRISM

    PRISM is a code name for a program under which the United States National Security Agency (NSA) collects internet communications from various U.S. internet companies. [1][2][3] The program is also known by the SIGAD US-984XN. [4][5] PRISM collects stored internet communications based on demands made to internet companies such as Google LLC and ...

  3. 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]

  4. Corrective lens - Wikipedia

    en.wikipedia.org/wiki/Corrective_lens

    Corrective lens. A pair of contact lenses, positioned with the concave side facing upward. A corrective lens is a transmissive optical device that is worn on the eye to improve visual perception. The most common use is to treat refractive errors: myopia, hypermetropia, astigmatism, and presbyopia.

  5. Convergence insufficiency - Wikipedia

    en.wikipedia.org/wiki/Convergence_insufficiency

    The symptoms and signs associated with convergence insufficiency are related to prolonged, visually demanding, near-centered tasks. They may include, but are not limited to, diplopia (double vision), asthenopia (eye strain), transient blurred vision, difficulty sustaining near-visual function, abnormal fatigue, headache, and abnormal postural adaptation, among others.

  6. Accommodative convergence - Wikipedia

    en.wikipedia.org/wiki/Accommodative_convergence

    Accommodative convergence is that portion of the range of inward rotation of both eyes (i.e., convergence) that occurs in response to an increase in optical power for focusing by the crystalline lens (i.e., accommodation). [1] When the human eye engages the accommodation system to focus on a near object, signal is automatically sent to the ...

  7. Prism (optics) - Wikipedia

    en.wikipedia.org/wiki/Prism_(optics)

    Prism (optics) A familiar dispersive prism. An optical prism is a transparent optical element with flat, polished surfaces that are designed to refract light. At least one surface must be angled — elements with two parallel surfaces are not prisms. The most familiar type of optical prism is the triangular prism, which has a triangular base ...

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