null

Stop Right There: Your Eyeglasses Script Won't Work for Contact Lenses

9th Jul 2025

eyeglasses-vs-contact-lens-prescription-lensesonline-nz

Just picked up your new glasses prescription and thinking about grabbing some contacts for summer? Hold up, mate.

You can't use your glasses prescription to buy contact lenses. 

This is the number one mistake we see Kiwis make, and it's a fast track to wasted money and potentially damaged eyes. Let's sort this out properly.

It's All About Distance and Design

1. Distance Changes Everything

Picture this: holding a magnifying glass right on a page versus holding it 12mm away. A completely different effect, right?

Your glasses sit 12mm from your eyes. Contacts sit directly on them. This gap (called vertex distance) completely changes the power needed to focus light properly.

If your prescription is stronger than ±4.00, this difference is massive and must be calculated by an optometrist.

2. Contacts Are Medical Devices, Not Just Lenses

Beyond the power calculation, contacts must fit your exact corneal shape. Get this wrong and you're looking at:

  • Discomfort (like wearing shoes two sizes too small)
  • Reduced oxygen flow
  • Blurry vision
  • Risk of infection

Your glasses script has zero information about how a lens should fit your eye.

Eyeglasses vs. Contact Lens Prescription

Glasses Prescription Covers:

  • Sphere (SPH): Your main vision correction
  • Cylinder (CYL): Astigmatism correction power
  • Axis: Angle of astigmatism correction

Contact Lens Prescription Adds:

  • Base Curve (BC): Exact curvature to match your cornea
  • Diameter (DIA): Lens width for proper coverage
  • Brand & Material: Chosen for your eye's specific oxygen and moisture needs

The Astigmatism Headache: Why Your Numbers Don't Exist

Here's where most Kiwis hit a wall:

Your cylinder power isn't made - Got -0.50 cylinder on your glasses script? Most soft contacts aren't manufactured with this power. An optometrist must clinically decide how to compensate.

Your axis is too precise - Glasses can be made to exact angles like 93°. Contacts are mass-produced in set steps (usually multiples of 10: 70°, 80°, 90°). Your optometrist chooses the closest fit that actually works.

The Right Way Forward: The Contact Lens Fitting

Step 1: The Fitting

A dedicated appointment where your optometrist:

  • Measures your Base Curve and Diameter
  • Assesses your eye health and tear film
  • Determines the right brand and material

Step 2: Trial Period

You'll wear trial lenses for about a week to ensure they stay comfortable and your vision remains clear throughout normal daily wear.

Step 3: Official Prescription

After successful trials, you get your final contact lens prescription. By law, you must be given a copy. This is what you need to order contact lenses from us.

Feeling Stuck? Let's Make It Easy

We know this can seem complicated when all you want is to order your lenses. Got a prescription but not sure what to do next? Email us at sales@lensesonline.co.nz with a clear photo of your prescription, and we'll check it for free and tell you straight up if it's for glasses or contacts, and what your next step is.

Resources: