Contact Lens Prescriptions Explained: Decode Yours in Minutes

You've just had an eye test and walked out with a new prescription for contact lenses. But when you look at it, it's like reading a foreign language: OD –2.75 | CYL –0.75 | AXIS 180 | BC 8.6 | DIA 14.0.

What's it all mean? Can you use it to buy contact lenses online? And why can't you just use your glasses prescription instead?

Here's what you need to know – with the specific info that matters.

Decode Your Prescription Fast

Use this quick reference to match your contact lens order to your prescription.

Quick rule: Match all parts of your prescription (SPH, CYL, AXIS, BC, DIA, Brand) when buying.

Ready to Buy?

Once you’ve decoded your prescription, ordering online in New Zealand is easy. Visit LensesOnline.co.nz and enter the following details:

• Choose your lenses - e.g. 1-Day Acuvue Moist, Acuvue Oasys.
• Select your Base Curve (BC) – this sets how the lens fits your eye.
• Enter your Sphere / Power (SPH / PWR) – the plus or minus number that corrects your vision.
• Add any other values – such as CYL and AXIS for astigmatism, or ADD for multifocals.
• Pick quantity per eye – how many boxes you’d like.
• (Optional) Choose a subscription – set up automatic re-orders so you never run out.

Confirm and checkout – your lenses will be shipped directly to you.

Just copy the numbers exactly as they appear on your prescription slip.

New Zealand Prescription Rules

How long they last: Most optometrists make contact lens prescriptions expire after 12 months. Glasses prescriptions usually last 2 years.

Your rights: You're entitled to a copy of your prescription. It's in the Health & Disability Commissioner's Code of Rights.

The legal bit: All contact lenses in NZ are regulated as medical devices by Medsafe. Even coloured or cosmetic ones need a prescription.

Situations You Might Face

“My BC is 8.6 but I only see lenses available in 8.7 - is that ok?” Say your prescription says BC 8.6 but the shop only has 8.7. That tiny 0.1 difference might make a big difference, it can affect how they fit. Check with your optometrist first.

“My optometrist prescribed a brand that’s out of stock - can I pick another?”

Don't just grab another brand with the same numbers. Different brands have different materials and shapes, even when the specs look identical.

However, some brands are ‘white labels’ so the name provided might be specific to that optometrist chain. There may be the original version available.

“I accidentally ordered –2.50 instead of –2.75.” - Even being 0.25 off can make things blurry. Always double-check those numbers match exactly.

Why Your Glasses Prescription Won't Work

Glasses and contact lens prescriptions aren't the same thing. Here's why:

Distance matters: Your glasses sit about 12mm away from your eyes. Contacts sit right on your eye. That changes how strong they need to be, especially if you've got a strong prescription.

Missing info: Glasses prescriptions don't tell you the base curve or diameter – and you need those for contacts to fit properly and safely.

Brand specifics: Contact prescriptions often specify the exact brand and material. Glasses ones don't.

Bottom line: your glasses prescription won't cut it for ordering contacts.

Getting the Right Fit

Base curve and diameter: Get these wrong and your lenses might feel uncomfortable, move around, or make your vision blurry. 

Brand differences: Two different brands can feel completely different, even with identical numbers on paper.

Don't use expired prescriptions: Old prescriptions increase your risk of poor fit and eye infections.

Special Types of Prescriptions

Got astigmatism? You'll see CYL (cylinder strength) and AXIS (which way it's oriented) on your prescription.

Need reading help, too? That's presbyopia. Look for ADD values (usually +0.75 to +2.50) and sometimes D/N notation (dominant/non-dominant eye).

Want coloured lenses? In NZ, these are still medical devices. You need a valid prescription even if your vision's perfect.

Common Questions

Can I switch brands if the numbers are the same? Nope. Different brands can fit very differently because of how they're made. Ask your optometrist first.

Do I need a prescription for coloured lenses in NZ? Yes. Medsafe treats them as medical devices, even the ones that don't correct your vision.

Can I buy contact lenses online?

Yes. You can buy contact lenses online in New Zealand, but only if you have a valid, up-to-date prescription from an optometrist.

When ordering from us, you’ll need to enter your prescription details (SPH, CYL, AXIS, BC, DIA, and brand). 

How long's my prescription good for? Usually 12 months, but check the expiry date that's printed on it.

What happens if I get the wrong base curve or diameter? Your lenses might feel uncomfortable, move around too much, or blur your vision. Getting the fit wrong can also be bad for your eye health.

You Might Also Want to Read

• Guide to Transitioning from Glasses to Contact Lenses — what to expect when making the switch.
• Eyeglasses vs Contact Lens Prescription NZ — a deeper look at the differences and why they matter in New Zealand.
• Can Contact Lenses Expire? Hidden Risks of Using Old Lenses — why expiry dates are more than just a formal requirement.
• Claim Back Your Lenses: Do Not Miss Out on Insurance Benefits — how insurance might help cover or refund your lenses.

References:

• https://www.medsafe.govt.nz/medicines/policy-statements/definition-of-med.asp
• https://www.hdc.org.nz/media/550hs5ih/code-of-rights_online_5-sept-2022.pdf
• https://precision.myalcon.com/au/prescription-101/