The Lens Index number (1.57, 1.61, 1.67, 1.71 or 1.74) refers to the degree of refraction the lens provides. This means how much the light that enters the lens is refracted (bent) as it passes through the lens. Lens Index is also related to the thickness of the lens. The higher the index, the thinner the lens will be. People with higher prescriptions should choose high-index lenses. There will be a recommended lenses for your prescription.
PD is the distance between your two pupils in millimeters. Having a correct PD on your glasses ensures that you are looking through the ideal spot in your lenses. If there is no PD on your prescription, you can check it with your doctor or measure it yourself.
Sphere(SPH) refers to the refractive correction in the prescription. Minus(-) values are for nearsightedness, and Plus(+) values are for farsightedness. If "PL" or "Plano" is written for the either SPH on your prescription, then you should select "0.00".
CYL(Cylinder) & Axis
Cylinder(CYL) refers to astigmatism. It can be either positive(+) or negative(-). Axis is recorded as an angle in degrees, between 0°and 180°. Therefore, if there is a CYL value on your prescription, then there must be an Axis for it.
If "DS" or "SPH" is noted for the either CYL on your prescription, it means you have no astigmatism.
The number sometimes written as "NV" or "Reading Addition" refers to near vision and is used for multifocal lenses and readers.
Prism is power, measured in diopters, used to correct vision displacement, like double vision or an eye turn. Most eyeglass prescriptions do not have prism correction. A prescription with prism will have two values per eye: a Prism (power) and Base (direction).
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