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  2. Corrective lens - Wikipedia

    en.wikipedia.org/wiki/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.

  3. Eyeglass prescription - Wikipedia

    en.wikipedia.org/wiki/Eyeglass_prescription

    Invert the sign of cylinder value. Add 90° to axis value, and if the new axis value exceeds 180°, subtract 180° from the result. For example, a lens with a vertical power of −3.75 and a horizontal power of −2.25 could be specified as either −2.25 −1.50 × 180 or −3.75 +1.50 × 090.

  4. Prism correction - Wikipedia

    en.wikipedia.org/wiki/Prism_correction

    A lens which includes some amount of prism correction will displace the viewed image horizontally, vertically, or a combination of both directions. The most common application for this is the treatment of strabismus. By moving the image in front of the deviated eye, double vision can be avoided and comfortable binocular vision can be achieved ...

  5. Subjective refraction - Wikipedia

    en.wikipedia.org/wiki/Subjective_refraction

    Step 1: Using the +/-0.50DS on the confirmation set to determine the initial best sphere correction. Step 2: Presenting the 0.50JCC initially @ 90deg to determine any presence of astigmatism on that axis. Step 3: The axis of the JCC must straddle the axis of the correcting cylinder in the trial frames, in both flip positions.

  6. Refractive error - Wikipedia

    en.wikipedia.org/wiki/Refractive_error

    Refractive errors are typically measured using three numbers: sphere, cylinder, and axis. Sphere: This number denotes the strength of the lens needed to correct your vision. A "-" indicates nearsightedness while a "+" indicates farsightedness. Higher numbers indicate more power in either direction. Cylinder: This number denotes the amount of ...

  7. Astigmatism - Wikipedia

    en.wikipedia.org/wiki/Astigmatism

    Hopefully, after this, the eye will focus all light on the same location at the retina, and the patient's vision will be less blurred. [medical citation needed] In against-the-rule astigmatism, a plus cylinder is added in the horizontal axis (or a minus cylinder in the vertical axis).