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  2. Vertex distance - Wikipedia

    en.wikipedia.org/wiki/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 the power of the lens relative to ...

  3. Intraocular lens power calculation - Wikipedia

    en.wikipedia.org/wiki/Intraocular_lens_power...

    The aim of an accurate intraocular lens power calculation is to provide an intraocular lens (IOL) that fits the specific needs and desires of the individual patient. The development of better instrumentation for measuring the eye 's axial length (AL) and the use of more precise mathematical formulas to perform the appropriate calculations have ...

  4. Focal length - Wikipedia

    en.wikipedia.org/wiki/Focal_length

    The optical power of a lens or curved mirror is a physical quantity equal to the reciprocal of the focal length, expressed in metres. A dioptre is its unit of measurement with dimension of reciprocal length, equivalent to one reciprocal metre, 1 dioptre = 1 m −1. For example, a 2-dioptre lens brings parallel rays of light to focus at 1 ⁄ 2 ...

  5. Snellen chart - Wikipedia

    en.wikipedia.org/wiki/Snellen_chart

    In the most familiar acuity test, a Snellen chart is placed at a standard distance: 6 metres. At this distance, the symbols on the line representing "normal" acuity subtend an angle of five minutes of arc, and the thickness of the lines and of the spaces between the lines subtends one minute of arc. This line, designated 6/6 (or 20/20), is the ...

  6. Eyeglass prescription - Wikipedia

    en.wikipedia.org/wiki/Eyeglass_prescription

    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. If an eye examination indicates that corrective lenses are appropriate, the prescriber generally ...

  7. Optic equation - Wikipedia

    en.wikipedia.org/wiki/Optic_equation

    In number theory, the optic equation is an equation that requires the sum of the reciprocals of two positive integers a and b to equal the reciprocal of a third positive integer c: [1] {\displaystyle {\frac {1} {a}}+ {\frac {1} {b}}= {\frac {1} {c}}.} Multiplying both sides by abc shows that the optic equation is equivalent to a Diophantine ...

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