Understanding how to read your contact lens prescription is incredibly important. Without understanding the metrics displayed on your prescription, you’ll likely end up with a box of lenses that don’t aid your vision or fit your eye.

We’ve created this super handy guide to help you understand your contact lens prescription and order the right lenses online with ease.

Where Can I Find My Contact Lens Prescription?

Your contact lens prescription can be located in three different places:

  • On the prescription note given to you by your optician
  • On the individual lens packet
  • On the side of your contact lens box

If you cannot find the prescription note nor have a box in your possession, get in touch with your optician for an updated record.

How To Read Your Contact Lens Prescription

Now that you know where to locate your prescription, it’s time to understand what information is displayed on it. The information presented will vary depending on eye condition and brand, but as a general rule of thumb, you can expect to find the following:

Brand Name

Contact lens solutions and materials vary between brands and by wear (daily, monthly, two weekly) and type (multifocal, toric lenses, silicone hydrogel), so knowing which one you’re used to is essential. If you’re reading the prescription from the contact lens box or packet, you will likely see the brand name labeled at the top. For example, in the image above, you can see that the contact lens is from the 1 Day Acuvue Moist  (Acuvue) range from Johnson & Johnson.

What Does OD/OS Mean?

It’s perfectly normal to have a different prescription in each eye - but how do you figure out what lens goes in what eye? This is where OD/OS comes into play.

Oculus dexter (OD) means “right eye” in Latin and oculus sinister (OS) means “left eye”. These simple initials will help you to quickly understand your left and right eye prescriptions.

What Does OU Mean?

Alternatively, if your prescription is the same in both eyes, you might see oculus uterque (OS). This is Latin for “both”.

What Does Base Curve (BC) Mean?

All contact lens prescriptions will feature ‘BC’, which stands for the base curve. This refers to how curved your lens is. The base curve numbers tend to range from 8-10, with 10 being the flattest it can be.

Opticians will always try to get the lens to mimic the natural curve of your eye as much as possible.

What Does Diameter (DIA) Mean?

Another important measurement that all contact lens prescriptions will display is the diameter (DIA). The DIA refers to the width of the contact lens from edge to edge. It is typically measured in millimeters, and the size will vary depending on how much of the eye needs to be covered.

Power (PWR)/Sphere (SPH)/Dioptre (D)

The power (PWR)/sphere (SPH)/dioptre (D) relates to the strength of your contact lens. Contact lenses cover a whole range of strengths and prescriptions always increase by 0.25, meaning you’ll never struggle to get a lens suited to what you require.

A plus sign (+) refers to a long-sighted prescription, and a minus sign (-) refers to short-sightedness. The further away the strength is from 0, the stronger it will be.

Expiry Date

The final important thing to look out for on your contact lens prescription is the expiry date. This is usually displayed next to a little timer symbol.

The expiry date won’t be too much of an issue if you wear lenses regularly, but if you only wear them on occasion, it’s important to make sure that they’re still in date. Out of date lenses must be thrown out as they can potentially harm your eyes if worn.

How To Read Prescriptions for Astigmatism

Your contact lens prescription will look a bit different if you have astigmatism (our most popular astigmatism lense is the Acuvue Moist astigmatism) While it still features most of the metrics listed above, there will be two other measurements to look out for - Cylinder and Axis.

Cylinder (CYL)

The cylinder (CYL) refers to the type of astigmatism you have. Similarly to the PWR/SPH/D metric, it will increase by 0.25 depending on how curved your eye structure is. This metric will always be displayed in minus (-) figures.

Axis (AX)

The axis (AX) metric is used to define how much astigmatism correction you need. This metric will always be measured between 0-180 degrees and will help to focus power on the area of your eye which needs it the most.

How To Read Prescriptions for Presbyopia

Last, but by no means least, those who need presbyopia/multifocal correction will see another metric displayed on their prescription - Addition (ADD).

Addition (ADD)

The additional power (ADD) metric refers to how much power is needed to have clear vision at close range. The ADD prescription will always sit between 0.50 and 3.00, but some brands may refer to it as low, medium or high, instead.

The Differences Between Glasses and Contact Lens Prescriptions

As you can see, there are many measurements to be aware of when it comes to getting a perfectly fitting contact lenses. What’s important to remember, though, is that you cannot use a glasses prescription when ordering some contact lenses.

Glasses and contact lens prescriptions will never be identical; with lenses sitting on the surface of your eyes and glasses perched further away, the power of the lens will have to vary.

It is highly unlikely that you will see the base curve (BC) or diameter (DIA) on your glasses prescription as these metrics are not relevant.


1. What does a lens prescription mean?

Your contact lens prescription is written by your optometrist. It is decided based on various eye checks and helps to ensure your eye correction (whether glasses or lenses) works properly.

2. Is a contact lens prescription the same as glasses?

No, contact lens prescriptions are not the same as glasses prescriptions. This is because glasses sit away from your eyes while lenses sit directly on your eyes. This positioning changes the type of prescription needed.

3. Do lens prescriptions expire?

It’s perfectly normal for vision to worsen as you age, which is why opticians recommend yearly checkups. Prescription expiry will depend on where you live - be sure to get checked every year to ensure it’s up to date.

4. How do you convert glasses prescription to contact lenses?

Unfortunately, you cannot convert your glasses prescription to a contact lens one. You will need to visit your optician and carry out a contact lens check to get a suitable prescription.

Do You Need More Information Regarding Your Lens Prescription?

There you have it - your contact lens prescription, explained! If you require further assistance, do not hesitate to get in touch.