What the numbers on your prescription mean
Optometrists write prescriptions in a shorthand nobody explains to you at the counter. Here is what each abbreviation stands for, so the paper in your hand stops being a cipher.
This page defines terms. It does not give advice. It cannot tell you what your eyes need, whether a number is high or low, or what to order. Only the eye doctor who examined you can do that. If something here does not match what you were told, believe them, not us.
- Sphere
- The main lens power, measured in diopters. A minus sign means nearsighted, where distance is blurry. A plus sign means farsighted. The further from zero, the stronger the lens.
- Cylinder
- The extra power that corrects astigmatism, which is when the eye is shaped more like a football than a basketball, so light focuses unevenly. A blank or zero here means no astigmatism correction.
- Axis
- A number from 1 to 180 that says at what angle the cylinder correction sits. It is an orientation, not a strength. Axis only appears when there is a cylinder value.
- Add
- Extra magnifying power in the lower part of the lens for close work. It appears on bifocal, trifocal and progressive prescriptions, and is always a plus number.
- Pupillary distance
- The distance between the centres of your pupils in millimetres. It positions the optical centre of each lens in front of each eye. Sometimes written as one number, sometimes as two (one per eye).
- Right eye and left eye
- OD is the right eye and OS is the left, from the Latin oculus dexter and oculus sinister. OU refers to both eyes. Each eye gets its own row because they rarely need the same correction.
- Prism and base
- A less common addition that shifts where the image lands, used when the eyes do not align the way they should. Base is the direction of that shift: up, down, in or out.
SPH
Example: -2.25 is a nearsighted prescription.
CYL
AXIS
ADD
PD
OD / OS
PRISM / BASE