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2. Prism correction - Wikipedia

   en.wikipedia.org/wiki/Prism_correction

   Prentice's rule is a formula to calculate the amount of prism correction in a lens based on decentration and lens power. It can be used for prescribing, tolerance control, or determining unprescribed prism in eyeglasses.

3. Eyeglass prescription - Wikipedia

   en.wikipedia.org/wiki/Eyeglass_prescription

   Learn how to interpret and write an eyeglass prescription that includes sphere, cylinder and axis components. Sphere and cylinder specify the power of the lenses, and axis defines the orientation of the cylinder relative to horizontal and vertical.

4. Subjective refraction - Wikipedia

   en.wikipedia.org/wiki/Subjective_refraction

   Subjective refraction is a clinical examination to determine the best corrected visual acuity for a patient. It involves using trial lenses, a Snellen chart, a pinhole occluder and a duochrome test to measure spherical and cylindrical refractive errors.

5. Prism cover test - Wikipedia

   en.wikipedia.org/wiki/Prism_Cover_Test

   The prism cover test (PCT) is an objective method to measure ocular misalignment or deviation of the eye. It involves using prism bars, occluder, and targets to neutralise the deviation and record the angle and base of the prism.

6. Refractive error - Wikipedia

   en.wikipedia.org/wiki/Refractive_error

   Refractive error, also called ametropia, is a problem with focusing light on the retina due to the shape of the eye and/or cornea. Learn about the common types (nearsightedness, farsightedness, astigmatism, presbyopia), causes, diagnosis, and treatment options.

7. Progressive lens - Wikipedia

   en.wikipedia.org/wiki/Progressive_lens

   The addition value prescribed depends on the level of presbyopia of the patient. In general the older the patient, the higher the addition. They are also known as multifocal lenses, progressive addition lenses (PAL), varifocal lenses, progressive power lenses, graduated prescription lenses, or progressive spectacle lenses.