Understanding Your Glasses Prescription, No Jargon
Your eye doctor handed you a prescription covered in codes and numbers, and none of it makes sense. That is normal, and it takes only a few minutes to fix.
Every line on a prescription describes exactly what your eyes see, and what they need in order to see clearly. Once you crack the code, you choose your glasses with confidence, you check that nothing was left out, and you know exactly what to ask your optician for. Here is the plain-language guide, line by line.
The key points
- OD is your right eye, OS your left. Each eye has its own values, and they are often different.
- The sign in front of the first number tells you almost everything: minus for myopia, plus for hyperopia.
- The addition only appears with presbyopia, usually from your forties onward.
One eye at a time: OD and OS
A prescription is always read one eye at a time. OD comes from the Latin oculus dexter, the right eye. OS, oculus sinister, sometimes written OG in French, is the left eye. Your two eyes rarely correct in the same way, which is why each line has its own numbers. If only one line is filled in, your correction is identical on both sides, which is rarer than people think.
Sphere, cylinder, axis: the three columns that count
The sphere (marked SPH) measures the power of the correction, expressed in dioptres. A number preceded by a minus corrects myopia, blurry distance vision. A number preceded by a plus corrects hyperopia, strain in near vision. The higher the number, the stronger the correction. A -1.00 is a light correction, a -6.00 a strong one.
The cylinder (CYL) and the axis always go together. They correct astigmatism, that slight irregularity in the curve of the eye that makes the image a little distorted. The cylinder gives the power, the axis gives the orientation, on a scale from 0 to 180 degrees. If those boxes are empty, you simply are not astigmatic.
To understand the differences between myopia, hyperopia, astigmatism and presbyopia in depth, our dedicated guide covers each condition with concrete examples.
The addition: the line for presbyopes
From your forties onward, the eye struggles to focus up close. This is presbyopia, a natural process, not an illness. Your prescription then adds a value, the addition (sometimes marked ADD), always preceded by a plus. It shows the extra power needed to read a menu or a phone screen.
An addition often means a choice of lenses: reading lenses alone, or progressive lenses that combine distance and near vision on a single surface. We break this choice down in our article on single vision or progressive lenses.
Pupillary distance: the number that is often missing
One last marker, absent from many prescriptions yet essential for fitting: the pupillary distance, the distance in millimetres between the centres of your two pupils. It ensures that the optical centre of each lens sits right in front of your pupil. A poorly measured distance tires the eyes, even with the right correction. At Maison Mata, we measure it in store as a matter of course, free of charge.
How long does a prescription stay valid
The rules vary from country to country, but a glasses prescription almost always has an expiry date, often one to three years, shorter for children and for strong corrections. Once that period is over, a new exam is needed, because eyesight changes. If yours is getting old, an eye exam resets the clock before you order anything.
A prescription you can read is already half of a great pair. The rest is our craft.
Come and decode it with us
Bring your prescription into one of our stores in Bali. Our opticians read it through with you, measure your pupillary distance and point you toward the right lenses, no more, no less. Workshop know-how, at an accessible price.
Find your nearest Maison Mata store
This article is for information only and does not replace the advice of an ophthalmologist or a qualified optician. For any question about your eyesight, consult a health professional.