How to Read Your Glasses Prescription: A Simple UK Guide
You have just had your eyes tested and walked away with a small piece of paper covered in numbers, abbreviations, and symbols. If it looks confusing, you are not alone - understanding how to read a glasses prescription is something many people in the UK find baffling the first time around.
The good news is that once you understand what each value means, your prescription makes complete sense. This plain-English guide explains every term you are likely to see on a UK glasses prescription - from SPH and CYL to ADD power and pupillary distance - so you can shop for prescription glasses online with full confidence.
What Does a UK Glasses Prescription Look Like?
A standard UK glasses prescription is usually laid out as a table with a row for each eye. You will see the right eye labelled as R or OD (from the Latin oculus dexter) and the left eye labelled as L or OS (oculus sinister). Some prescriptions also include a row labelled OU, which refers to both eyes together.
Here is what a typical UK glasses prescription might look like:
| Eye | SPH | CYL | AXIS | ADD | Prism | Base |
|---|---|---|---|---|---|---|
| R (Right) | -2.50 | -0.75 | 180 | +2.00 | - | - |
| L (Left) | -2.25 | -0.50 | 175 | +2.00 | - | - |
Not every column will always have a value. If a box is blank or shows DS (dioptre sphere) or Pl (plano), it simply means no correction is needed for that measurement in that eye. Let's go through each term one by one.
The Key Values on Your Glasses Prescription Explained
The sphere value is the most fundamental part of your prescription. It tells you the overall power of the lens needed to bring your vision into focus, measured in dioptres (D).
A negative SPH value (for example, -2.50) means you are short-sighted (myopic) - you can see things up close but have difficulty seeing clearly in the distance. The higher the negative number, the stronger the prescription needed.
A positive SPH value (for example, +1.75) means you are long-sighted (hyperopic) - you may find it easier to see things at a distance but struggle to focus on close objects. Again, the higher the number, the stronger the correction required.
If your SPH value is 0.00, Pl, or DS, it means no sphere correction is needed in that eye.
These two values work together and are both needed when you have astigmatism. You will never see one without the other.
Astigmatism occurs when the cornea or lens of the eye is not a perfect sphere - it is more like a rugby ball than a football. This causes blurred or distorted vision at all distances. It is extremely common and nothing to worry about.
The CYL (cylinder) value indicates the degree of astigmatism correction needed. Like the SPH value, it is measured in dioptres and can be positive or negative depending on how your optician records it.
The AXIS value is a number between 1 and 180, indicating the orientation - or angle - of the astigmatism in the eye. It tells the lens maker which direction to align the corrective power in the lens.
If the CYL column on your prescription is blank, contains DS, or shows 0.00, you do not have astigmatism that requires correction - and no AXIS value will be needed either.
The ADD value is the extra magnifying power added to the bottom portion of the lens to help with near vision - typically for reading, using a phone, or close-up work.
ADD is most commonly found on prescriptions for people over 40 who are experiencing presbyopia - the gradual reduction in the eye's ability to focus on close objects that comes with age. It is a natural part of getting older and affects almost everyone eventually.
The ADD value is always positive and is usually the same for both eyes. It typically ranges from +0.75 to +3.50. If your prescription includes an ADD value, it means your optician is recommending bifocal or progressive (varifocal) lenses - or that you may benefit from a separate pair of reading glasses.
Prism values are prescribed for people whose eyes do not align correctly - a condition where the eyes point in slightly different directions, causing double vision or eye strain.
The Prism value indicates the amount of prismatic correction needed, measured in prism dioptres (Δ). The Base value tells the lens maker the direction the prism should face - typically listed as Base In (BI), Base Out (BO), Base Up (BU), or Base Down (BD).
Prism correction is relatively uncommon. If your prescription does not include a prism value, this is perfectly normal - most people do not need one.
What Is Pupillary Distance (PD) and Why Does It Matter?
Your pupillary distance (PD) is the measurement in millimetres between the centre of your right pupil and the centre of your left pupil. It is a crucial measurement when ordering prescription glasses online because it ensures the optical centre of each lens aligns precisely with your eyes.
If the PD is incorrect, even a perfectly written prescription will not give you the clearest, most comfortable vision - particularly for distance correction and progressive lenses.
PD is usually recorded in one of two ways:
- Single PD - one combined measurement for both eyes together, typically between 54mm and 74mm for adults
- Dual PD (or monocular PD) - a separate measurement for each eye individually, for example 32mm (right) / 31mm (left)
In the UK, opticians are not legally required to include your PD on your prescription - some do, some do not. If yours is not included, you can ask your optician to measure and provide it. You can also measure it yourself at home reasonably accurately using a ruler and a mirror, though having it done professionally is always preferable for progressive lenses.
How Long Is a UK Glasses Prescription Valid For?
In the UK, a glasses prescription is typically valid for two years for adults. For children under 16, or for people with certain eye conditions, it may be valid for a shorter period - your optician will advise you on this.
It is worth keeping track of when your prescription was issued. Ordering glasses using an expired prescription is not recommended, as your vision may have changed in the meantime - and an incorrect prescription can cause eye strain and headaches.
If you are not sure whether your prescription is still valid, the simplest solution is to book a new eye test. Most high-street opticians and independent practices in the UK recommend a full eye examination every two years as standard.
Can I Use My Glasses Prescription to Order Online in the UK?
Yes - absolutely. Buying prescription glasses online in the UK is straightforward, legal, and can save you a significant amount compared to the high street. You simply need a valid prescription from a registered UK optician and your pupillary distance measurement.
At Urban Optics, you can add your prescription to any frame in our collection at checkout. We offer a wide range of lens types to match your needs:
- Single vision lenses - for distance or reading correction only
- Progressive and bi-focal lenses - for prescriptions with an ADD value
- Blue light lenses - ideal for screen use, available with any prescription
- Transition lenses - lenses that darken in sunlight
- Prescription sunglasses - your prescription built into sunglass frames
- Drive Safe lenses - designed to reduce glare specifically for driving
Free UK delivery is available on orders over £50, with free returns - so there is no risk in trying.
Tips for Ordering Prescription Glasses Online in the UK
If you are ordering prescription glasses online for the first time, here are a few things that will help the process go smoothly:
- Check your prescription date - make sure it is less than two years old before placing an order
- Have your PD ready - if it is not on your prescription, ask your optician or measure it yourself before ordering
- Consider the lens type you need - if your prescription includes an ADD value, you will need progressive or bifocal lenses rather than single vision
- Check the frame dimensions - particularly lens height if you are ordering progressive lenses, which need at least 28-30mm of vertical space
- Use virtual try-on - Urban Optics offers a virtual try-on tool so you can see how frames look on your face before buying
Understanding Your Prescription: A Quick Reference Summary
| Term | What It Means | What to Look For |
|---|---|---|
| SPH (Sphere) | Overall lens power | Minus = short-sighted, Plus = long-sighted |
| CYL (Cylinder) | Astigmatism correction strength | Blank or DS = no astigmatism |
| AXIS | Direction of astigmatism | Number between 1-180, always paired with CYL |
| ADD | Extra near vision power | Always positive - means you may need progressive/bifocal lenses |
| Prism / Base | Eye alignment correction | Uncommon - not present on most prescriptions |
| PD | Pupillary distance in mm | Essential for ordering online - ask optician if not listed |
| R / OD | Right eye | Always the first row on a UK prescription |
| L / OS | Left eye | Always the second row on a UK prescription |
Frequently Asked Questions
How do I know if I am short-sighted or long-sighted from my prescription?
Look at your SPH value. A negative number (e.g., -1.75) means you are short-sighted and struggle to see things in the distance. A positive number (e.g., +2.00) means you are long-sighted and may find close-up tasks more difficult.
What does it mean if my CYL column is blank?
It means you do not have astigmatism that requires correction. Your lenses will be made to the SPH value only, without any additional cylinder correction.
Do I need progressive lenses if my prescription has an ADD value?
Not necessarily - but it is the most common recommendation. An ADD value means your optician is prescribing additional near vision correction. You can get this as progressive lenses (varifocals), bifocals, or as a separate pair of reading glasses. Progressive lenses handle all distances in one pair, which most people find the most convenient option.
My optician did not include my PD on my prescription. What should I do?
Simply ask your optician to measure and provide it - they are required to do so if you request it. You can also measure your PD at home using a ruler and a mirror, or use an online PD measurement tool. For progressive lenses in particular, we recommend having this measured professionally.
How long is a glasses prescription valid for in the UK?
For most adults, a UK glasses prescription is valid for two years from the date of issue. If your prescription is older than this, you will need a new eye test before ordering prescription glasses.
Can I order glasses online from Urban Optics using my UK prescription?
Yes. Simply choose your frames, select your lens type, and enter your prescription details at checkout. If you have any questions about your prescription or which lens is right for you, our team is happy to help.
Ready to order prescription glasses online? Browse our full collection of frames and add your prescription at checkout - with free UK delivery over £50 and free returns.
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