Eyeglass Prescription Positive Cylinder Conversion

Ophthalmologists and a few older optometrists (different types of eye doctors), write astigmatism prescriptions with positive (+) cylinders. This is because many years ago the instruments used to measure and cut lenses were only able to do so in positive increments.

Nowadays the majority of labs, including ours, cut lenses in the negative (-), and require that any positive (+) cylinder prescriptions be converted into the negative (-) equivalent. Rest assured this conversion does not alter the type or quality of the vision correction that your doctor prescribed you. The conversion will affect (change) the SPH, CYL, and AX parameters in your prescription, but will result in the exact same vision correction you were fit for by your doctor.

We automatically perform this conversion if the prescription you enter is written with a positive (+) cylinder, but if you would like to get the conversion of your positive cylinder prescription, you can do so by using the Positive Cylinder Conversion tool.