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Positive Cylinder converter

Sphere Cylinder Axis

Why are some presciptions written with + cylinder and others in - cylinder? How do I convert?

Some ophthalmologists and a few older optometrists write prescriptions in plus cyl form. Many years ago, refracting instruments and spectacle lenses were ground with the cylinder correction on the convex, front surface and hence the rationale for plus cy l notation. During the last 20 years or so, most refracting instruments and nearly all spectacle lenses have been ground with the cyl correction on the concave, rear surface. There are resulting subtle optical effects between these two lens manufacturing techniques and is more pronounced in higher powers. Optical purists would prefer that if your optical correction is measured in minus cyl, then your spectacle lenses should be ground in that manner and visa versa. Most optometrist consider plus cyl lens es archaic as they are difficult to find as stock lenses, although they can certainly be custom fabricated.

Using the converter above can translate +ve cylinder to -ve version. It's fast and easy.

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