When purchasing single vision eyeglasses, wearers with higher prescription-strength should be aware that a large frame with a wider lens is not recommended while smaller and narrower lens width will contribute to a thinner edge, lighter weight and greater comfort.
a. Applying higher index lenses (1.61 indexes and above) can solve the problem of having a thick edge on the Negative lens or a thick center of the Positive lens. These higher index lenses are not only thinner and lighter but being aspheric will effectively perfect your vision effect and wearing comfort.
b. For the farsighted wearers (There is
in front of SPH value) who want to select the higher index lens above the 1.61 index, please avoid choosing big frame with wide lens because the higher index positive lens is with a smaller diameter (55mm) which might be insufficient to be polished based on the frame with wild lens, the frame with the lens width of 50mm or shorter is recommended.
c. For the wears that have a comparatively small PD (the distance between your pupils is less than 58mm), please pay more attention to the total width of the size as a larger frame may not match your PD. A smaller frame with a lens width of 50mm or lower should be considered as the first choice in order to make sure the accuracy of 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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