OD, OS, BC...What Your Contact Lens Script Is Actually Saying

23rd Sep 2025

Lensworld.com.au OD, OS, BC...What Your Contact Lens Script Is Actually Saying

Just got your first contact lens prescription, and it looks like a jumble of numbers and letters — OD, OS, BC, DIA? Don’t worry, it’s not as complicated as it seems.

Here’s a simple breakdown of what each part means and why it matters for your eyes.

Glasses vs Contact Lens Prescriptions

First things first: you can’t use your glasses prescription to buy contact lenses.

Glasses sit a short distance away from your eyes, while contacts sit directly on them. Because of that, contact lens prescriptions include extra measurements to make sure the lens actually fits, not just corrects your vision.

What the Numbers and Letters Mean

Here’s a breakdown of the main abbreviations you’ll see:

Abbreviation	Stands for	What it means	Example
OD	Oculus Dexter	Right eye	−2.75
OS	Oculus Sinister	Left eye	−3.00
SPH / PWR	Sphere / Power	Strength of correction. − = nearsighted; + = farsighted.	−2.75
CYL	Cylinder	Astigmatism correction (if needed)	−0.75
AXIS	Axis	Angle (0–180°) for astigmatism	180
BC	Base Curve	Curve of lens to match cornea	8.6
DIA	Diameter	Size of lens (mm)	14.0
ADD	Addition	Extra near power (multifocals)	+1.50
Brand	Lens type/material	Specific lens design/manufacturer	Acuvue Oasys

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

Ready to Order?

Once you’ve made sense of your prescription, buying contact lenses online in Australia is pretty straightforward. Visit https://www.lensworld.com.au/ and do the following:

Choose your lenses – e.g. Acuvue Oasys, Dailies Total 1, or whichever brand your optometrist prescribed.
Select your Base Curve (BC) – this number 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 multifocal lenses.
Pick quantity per eye – how many boxes you’d like for the left and right.
(Optional) Set up a subscription – you can schedule automatic reorders so you don’t run out.

Confirm and checkout – your lenses are shipped straight to your door. Copy the numbers exactly as they appear on your prescription slip.

Why Fit Matters (Base Curve & Diameter)

Those “extra” numbers — base curve and diameter — are what make a contact lens prescription different from glasses.

If the BC is wrong, the lens might feel too loose or too tight.

If the DIA is off, the lens may not cover your eye properly, which can affect comfort and clarity.

It’s not just about how sharp you can see but also about keeping your eyes safe and healthy.

How Long Does a Prescription Last in Australia?

Most contact lens prescriptions are valid for 12 months. After that, you’ll need a check-up before reordering.

It’s partly a legal requirement, but it also gives your optometrist a chance to make sure your eyes are still healthy and your vision hasn’t changed.

Common Questions About Contact Lens Prescriptions

Can I swap contact lens brands if the power is the same?

Not without your optometrist’s approval. Different brands have unique shapes and materials, so even with the same power, the fit and comfort may be very different.

Why are my left and right eyes different?

Very normal — most people’s eyes need different corrections.

What happens if I order the wrong base curve?

The lenses might still go in, but they may feel uncomfortable, move too much, or blur your vision. Always stick to the BC your optometrist prescribes.

The Takeaway

Your contact lens prescription isn’t as complicated as it first looks. Once you know what OD, SPH, BC and DIA stand for, you’ll be able to read it and order your contact lenses online easily.

And remember: in Australia, you’ll always need a valid contact lens prescription to buy lenses, whether online or in-store. If in doubt, just ask your optometrist — they’ll happily walk you through it.