You have just had your eye test and you are holding a prescription that looks like a maths problem. Here is what it all means.
SPH (Sphere)
This is the main power of your lens. A minus number means you are short-sighted — you see close things clearly but distant things are blurry. A plus number means you are long-sighted — distant things are clearer but close work is harder. The bigger the number, the stronger the prescription.
CYL (Cylinder) and Axis
These two numbers together describe astigmatism — a slight irregularity in the shape of your cornea that causes blurring at certain angles. Many people have mild astigmatism and do not even know it. The Axis number (0–180) tells the lens manufacturer which direction to orient the correction.
ADD
This appears on prescriptions for reading glasses or progressive lenses. It is an additional magnification for close-up vision, typically prescribed for people over 40.
PD (Pupillary Distance)
The distance between your pupils in millimetres. This number ensures the optical centre of your lens lines up exactly with your eye. Getting this wrong causes eye strain even with a correct prescription.
OD and OS
Latin abbreviations — OD means right eye (oculus dexter), OS means left eye (oculus sinister). Your two eyes almost always have different prescriptions.
If you have questions about your prescription, our optometrists at Vision Rabbit are happy to walk you through it. Understanding your own vision is the first step to taking care of it.