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How to read your eye prescription
Next in this series: types of eyeglass lenses explained and buying glasses online in Pakistan.
Your prescription is a short list of numbers that tells a lab how to make your lenses. This guide explains each part in plain words. You can also type your numbers into our prescription decoder.
The parts of a prescription
| Term | What it means |
|---|---|
| OD | Right eye |
| OS | Left eye |
| OU | Both eyes |
| SPH (sphere) | The main lens power, measured in dioptres (D). A minus sign (-) means short sight, so distant things look blurry. A plus sign (+) means long sight, so close things can look blurry. |
| CYL (cylinder) | Extra power for astigmatism, where the eye is shaped more like a rugby ball than a football. If this box is empty, you have no astigmatism correction. |
| AXIS | The direction of the cylinder, from 1 to 180 degrees. It only appears when there is a CYL value. |
| ADD | Extra power for close work, used in reading, bifocal and progressive lenses. It is usually between +0.75 and +3.00. |
| PD | Pupil distance in millimetres, the gap between the centres of your pupils. Most adults are between about 54 and 74 mm. |
A worked example
| SPH | CYL | AXIS | |
|---|---|---|---|
| OD (right) | -2.00 | -0.50 | 180 |
| OS (left) | -1.75 | -0.25 | 170 |
PD 62 mm. This person is short-sighted in both eyes (the minus signs), has a small amount of astigmatism, and needs slightly more power in the right eye. There is no ADD, so a single vision lens is enough.
Reading the size of the numbers
- The further a number is from zero, the stronger the lens. -4.00 is stronger than -1.00.
- Strong prescriptions can make thick lenses. High-index lenses are thinner.
- It is normal for the two eyes to have different numbers.
How long is a prescription good for?
Many opticians suggest an eye test every one to two years, and sooner if your vision changes or you get headaches. Children are usually tested more often because their eyes are still changing. Book an eye test if you are unsure.
Next steps
- Measure your PD with our PD tool if it is not on your prescription.
- Choose a lens type, or try Which Lens Do I Need.
- Learn the difference between progressive and bifocal lenses.
- See how to order prescription glasses online.