How to Read Your Eye Prescription

If you’ve ever looked at your eye prescription and thought it resembled a secret code – you’re not alone. Terms like SPH, CYL, and AXIS can feel confusing at first glance.

But here’s the good news: once you understand what each part means, your prescription becomes simple – and even empowering.

Let’s break it down clearly so you know exactly what your numbers means and how they affect your vision.

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What is an Eye Prescription?

Your eye prescription is a set of measurements that tells us how to correct your vision using glasses or contact lenses. It identifies common refractive errors like:

• Myopia (short-sightedness) – blurry distance vision
• Hyperopia (long-sightedness) – blurry near vision
• Astigmatism – distorted or blurred vision at all distances

Each eye is measured separately, which is why you’ll usually see:

• OD (Right Eye)
• OS (Left Eye)

The 3 Key Numbers Explained

Let’s focus on the most important parts of your prescription: SPH, CYL, and AXIS.

1. SPH (Sphere): Your Main Vision Power

SPH tells you the strength of your prescription in diopters (D).

• A minus (-) value means you are short-sighted (myopic)
• A plus (+) value means you are long-sighted (hyperopic)
• A value of 0.00 means no correction is needed

Example:

• -2.00 SPH = mild short-sightedness
• +1.50 SPH = mild long-sightedness

The higher the number, the stronger the prescription.

2. CYL (Cylinder): Astigmatism Correction

CYL measures how much astigmatism you have.

Astigmatism occurs when the front surface of your eye (cornea) isn’t perfectly round, causing blurred or distorted vision.

• If CYL is blank or 0.00, you likely don’t have astigmatism.
• If it has a value, you need additional correction

Example:

• CYL -1.00 = mild astigmatism
• CYL -2.50 = stronger astigmatism

3. AXIS: The Direction of Astigmatism

AXIS works together with CYL.

It tells us the orientation (angle) of your astigmatism – measured from 0 to 180 degrees.

• It’s not a strength, but a direction
• Without AXIS, CYL cannot be applied correctly

Example

• AXIS 90 = vertical orientation
• AXIS 180 = horizontal orientation

Think of it like setting the angle of a camera lens – it ensures your vision is corrected precisely.

A Simple Prescription Example

Here’s what a typical prescription might look like:

What this means:

Right eye (OD): 

• Short-sighted (-2.00)
• Moderate astigmatism (-1.00)
• Axis at 180 degrees

Left eye (OS):

• Mild short-sighted (-1.50)
• Mild astigmatism (-0.50)
• Axis at 90 degrees

Other Terms You Might See

While SPH, CYL, and AXIS are the core components, your prescription may also include:

ADD (Addition)

Extra magnification for reading or close work – common over age 40.

PD (Pupillary Distance)

Distance between your pupils – ensures lenses are centred correctly.

Prism

Used to correct eye alignment issues like double vision.

Why Understanding Your Prescription Matters

Knowing how to read your prescription helps you:

• Make confident decisions when buying glasses
• Understand changes in your vision over time
• Communicate better with your optometrist
• Avoid costly mistakes when ordering lenses online

Most importantly, it gives you control over your eye health.

Your eye prescription isn’t just a set of numbers – it’s a personalised map of your vision.

Once you understand SPH, CYL, and AXIS, everything becomes much clearer (literally and figuratively).

If you’re unsure about your prescription or noticing changes in your vision, the best step is always a comprehensive eye test.

Need Help Understanding your Prescription?

If you’re in Adelaide and want a personalised explanation, we’re always happy to walk you through your results and ensure you’re seeing your best.