A prescription for glasses contains valuable information about your visual needs and vision correction. For those who have little or no optical knowledge, how a prescription for a pair of glasses is written looks like a bunch of messy symbols, letters and numbers. Every ingredient in the prescription for glasses represents a very important value that tells your ophthalmologist a lot about your eye, vision and vision correction needs.


Sphere (SPH)

Cylinder (CYL)



Right Eye (OD)





Left Eye (OS)





Pupillary Distance



OD: Stands for “oculus dextrus”, Latin word for your right eye.

OS: Stands for “oculus sinister”, Latin word for the left eye.

Sphere (SPH): This indicates the lens power, prescribed to correct nearsightedness or farsightedness.

If there is a minus sign (–) in front, you are nearsighted

If there is a plus sign (+) in front, you are farsighted

Cylinder (CYL): It shows the lens power for astigmatism. The absence of this column means either you have no astigmatism, or it's very small that it is not necessary to correct it.

If the number has a minus sign (–), you have a nearsighted astigmatism

If the number has a plus sign (+), you have a farsighted astigmatism

Cylinder power is always after sphere power in an eyeglass prescription.

Axis: he axis shows the location of the sphere and cylinder powers on the lens. It ranges from 1-180.

PD: Stands for “pupillary distance”, the distance between your pupils.

ADD: This is the additional reading lens power for the lower segment on your progressive lenses.

Prism Correction: This correction is for those who either have exotropia or esotropia.


If there is a CYLINDER, there must be an AXIS.

If there is an AXIS, there must be a CYLINDER.

CYLINDER values must be either both positive or both negative values.

If it says “SPH” or “SPHERE” for you CYLINDER, that means that there is only a correction for your sphere, not that they have the same value.

If you order progressive/bifocal lenses, your prescription must have an ADD value.

If you have an Rx for progressive lenses but want to order single vision lenses for reading, then you will have to convert your Rx by simply adding the ADD values to your SPH, and that’ll be your new SPH.

For single vision for distance lenses, you can ignore your ADD values and just use the rest of the Rx normally