Understanding Your Prescription
Everything you need to know about your glasses prescription, explained simply.
Your prescription is simply a set of instructions
Those numbers on your prescription might look intimidating, but they're really just instructions. They don't tell us whether your eyes are "good" or "bad." They simply describe how light needs to be focused so you can see clearly. Once you understand what each number means, your prescription becomes much less mysterious.
Your prescription at a glance
Every glasses prescription follows the same basic format. Your right and left eye are listed separately, while each column contains a different measurement that helps determine how your lenses should be made. Some measurements will appear on every prescription, while others are only included if they're needed.
You don't need to memorise every abbreviation, but understanding the basics will make it much easier to read your prescription, compare changes over time and confidently order glasses online.
Let's look at what each of those measurements actually means.
What the numbers mean
SPH (Sphere)
Every glasses prescription contains an SPH value. This is the main lens power that corrects either short-sightedness (minus values) or long-sightedness (plus values), helping you see clearly.
CYL & AXIS
Most people also have a CYL and AXIS value. These work together to correct astigmatism.
Astigmatism simply means that your eye isn't perfectly spherical. Instead of focusing light evenly, it bends differently in different directions. The CYL value tells us how much correction is needed, while the AXIS tells us exactly where that correction should be placed.
If you don't have astigmatism, these boxes may be left blank or simply show DS.
ADD
From around the age of 45, most people begin to notice that reading becomes more difficult. This is called presbyopia and happens naturally as the eye's focusing system ages.
The ADD value is an additional reading power added to your prescription. It is combined with your distance prescription to make single vision reading glasses or varifocal lenses.
As your reading addition increases (often around +2.00), you may also begin to notice that intermediate tasks such as computer work or seeing the dashboard in the car become more difficult.
PD (Pupillary Distance)
Unlike the other measurements, your PD isn't actually part of your prescription. It's a separate measurement that records the distance between the centres of your pupils in millimetres.
Your optician may include it on your prescription, but they don't always, as it's used to position your lenses correctly within your chosen frames rather than determine your lens power.
If you don't have your PD measurement, don't worry. We can help you measure it accurately before your glasses are made, ensuring your lenses are centred correctly for the clearest and most comfortable vision possible.
Did you know?
Your CYL value may be written as either a plus (+) or minus (-) number.
They're simply two different ways of writing exactly the same prescription. Converting between them changes the SPH, CYL and AXIS values together, but the finished lenses remain identical.
Common Questions
Will wearing my glasses make my eyes weaker?
This is one of the biggest myths we hear, but thankfully it isn't true.
Wearing your glasses doesn't weaken your eyes or make them become dependent on lenses. Your prescription changes naturally over time, whether you wear your glasses every day or leave them in a drawer.
What often happens is much simpler. Once you've experienced clear, comfortable vision, you're much more aware of how blurred things look without your glasses. Taking them off doesn't make your eyesight worse – it simply removes the correction you've become used to.
Not wearing the correct prescription may also leave you working harder to focus, which can contribute to headaches, eye strain and tired eyes.
Is my prescription considered strong?
±0.25 to ±2.00 = Mild prescription
±2.25 to ±5.00 = Moderate prescription
Above ±5.00 = Strong prescription
Remember, a stronger prescription doesn't necessarily mean poorer eye health. It simply means your lenses need to provide more correction to bring your vision into focus.
Why are my two eyes different?
Perfectly normal.
Very few people have exactly the same prescription in both eyes. Each eye develops independently, so it's common for one eye to require a little more correction than the other.
How often should my prescription change?
For many adults, prescriptions remain stable for several years, while others change regularly over time. That's why regular eye examinations are important — not just to update your glasses, but to monitor the health of your eyes.
Your prescription is only part of the story
Your prescription tells us how to create lenses that help you see clearly, but it's only one part of finding glasses you'll love wearing.
The right frame size, lens design and accurate positioning all play an important role in how comfortable and natural your finished glasses will feel. That's why we don't simply ask you to upload a prescription and hope for the best.
Instead, we guide you through each step, helping you choose frames that suit you and collecting any additional measurements needed to ensure your glasses are made as accurately as possible.
Whether you're buying your first pair online or replacing an old favourite, we're here to make the process simple, straightforward and enjoyable.
Need a hand choosing your glasses?
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