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2. Vertex distance - Wikipedia

   en.wikipedia.org/wiki/Vertex_distance

   Since most refractions (the measurement that determines the power of a corrective lens) are performed at a vertex distance of 12–14 mm, the power of the correction may need to be modified from the initial prescription so that light reaches the patient's eye with the same effective power that it did through the phoropter or trial frame.

3. Prism correction - Wikipedia

   en.wikipedia.org/wiki/Prism_correction

   Individuals with nystagmus, Duane's retraction syndrome, 4th Nerve Palsy, and other eye movement disorders experience an improvement in their symptoms when they turn or tilt their head. Yoked prism can move the image away from primary gaze without the need for a constant head tilt or turn. [1] Prism correction is measured in prism dioptres. A ...

4. Ophthalmic trial frame - Wikipedia

   en.wikipedia.org/wiki/Ophthalmic_trial_frame

   A trial frame is a tool used by ophthalmic professionals like ophthalmologists and optometrists. It is basically an adjustable spectacle frame with multiple cells, used to hold corrective lenses , and other accessories in subjective refraction (finding the correct spectacle power) and retinoscopy .

5. Adjustable-focus eyeglasses - Wikipedia

   en.wikipedia.org/wiki/Adjustable-focus_eyeglasses

   Adjustable focus eyeglasses have one focal length, but it is variable without having to change where one is looking. Possible uses for such glasses are to provide inexpensive eyeglasses for people from low-income groups, developing countries, third world countries or to accommodate for presbyopia.

6. Astigmatism (optical systems) - Wikipedia

   en.wikipedia.org/wiki/Astigmatism_(optical_systems)

   Astigmatism causes difficulties in seeing fine detail. Astigmatism can be often corrected by glasses with a lens that has different radii of curvature in different planes (a cylindrical lens), contact lenses, or refractive surgery. [5] Astigmatism is quite common. Studies have shown that about one in three people suffers from it.

7. Dioptric correction - Wikipedia

   en.wikipedia.org/wiki/Dioptric_correction

   At the bottom of the image: the eyeglass. Dioptric correction [1] is the expression for the adjustment of the optical instrument to the varying visual acuity of a person's eyes. It is the adjustment of one lens to provide compatible focus when the viewer's eyes have differing visual capabilities.

8. Tilt (optics) - Wikipedia

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

   Piston and tilt are not actually true optical aberrations, as they do not represent or model curvature in the wavefront. Defocus is the lowest order true optical aberration. If piston and tilt are subtracted from an otherwise perfect wavefront, a perfect, aberration-free image is formed. Rapid optical tilts in both X and Y directions are termed ...

9. Aspheric lens - Wikipedia

   en.wikipedia.org/wiki/Aspheric_lens

   Lapping tool on a spindle below the lens, and mounting tool on a second spindle (swung out) uses pitch to hold the lens shown with its concave side down. The non-spherical curvature of an aspheric lens can also be created by blending from a spherical into an aspherical curvature by grinding the curvatures off-axis.