Understand SPH, CYL, Axis, BC, DIA & why toric lens prescriptions look different.
Cylinder and Axis
If your prescription includes Cylinder and Axis, you have astigmatism — and your contact lenses must be specially designed to correct it.
Astigmatism prescriptions can look confusing at first, but once you understand what each number means, they become simple and predictable.
This guide explains every part of an astigmatism prescription and shows you how to choose the right toric contact lenses based on your own numbers.
Example of a Toric Prescription
A typical astigmatism contact lens prescription looks like this:
–2.50 / –1.25 × 180
This includes:
- Sphere (SPH) – overall correction
- Cylinder (CYL) – astigmatism amount
- Axis – direction of astigmatism
When ordering contacts online, you will also see:
- Base Curve (BC)
- Diameter (DIA)
- Brand (mandatory for contacts)
Below we’ll explain each part in detail.
1. Sphere (SPH)
Your basic nearsighted or farsighted correction.
The Sphere value shows how much power your lenses need to correct nearsightedness or farsightedness.
SPH Format:
- A minus sign (–) means nearsighted (myopia)
- A plus sign (+) means farsighted (hyperopia)
- The number indicates the strength
Examples:
- –3.00 SPH → nearsighted
- +2.25 SPH → farsighted
- 0.00 SPH → neither (rare)
Astigmatism exists in addition to this correction.
2. Cylinder (CYL)
The amount of astigmatism you have.
Cylinder shows the difference in curvature between the steepest and flattest parts of your cornea.
CYL is always a negative number for soft toric lenses.
Common CYL ranges in prescriptions:
- –0.50
- –0.75
- –1.25
- –1.75
- –2.25
- –2.75 (some brands)
Higher CYL = stronger astigmatism
Example:
A person with –1.25 CYL has more astigmatism than someone with –0.75 CYL.
3. Axis
The orientation (angle) of your astigmatism, measured in degrees.
Astigmatism isn’t the same in all directions — your cornea is shaped differently along certain angles.
The Axis shows where the astigmatism curvature is located.
Axis is always between 0 and 180 degrees.
Examples:
- 180° (horizontal meridian)
- 90° (vertical meridian)
- 45° (diagonal/oblique)
The axis does not represent power — it simply tells the lens how to align with your eye.
CYL + Axis Always Work Together
If your prescription includes a CYL number, it must include an Axis.
Example:
-1.25 CYL × 180
-0.75 CYL × 90
-2.25 CYL × 45
This pair tells the lens two things:
- How much correction is needed
- Where to place it
This is why toric lenses use stabilization designs — the orientation must remain constant.
4. Base Curve (BC)
How the lens fits your eye.
BC describes the curvature of the back of the contact lens.
Common BC values:
- 8.4
- 8.5
- 8.6
- 8.7
Manufacturers design each brand with its own BC — you don’t choose your BC; your optometrist does.
5. Diameter (DIA)
The overall size of the lens.
Soft contact lenses typically have a DIA of:
- 14.0
- 14.2
- 14.5
The base curve and diameter together determine fit — critical for toric lens stability.
6. Brand (Mandatory for Contacts)
Unlike glasses, contact lens prescriptions are brand-specific.
That’s because:
- Each brand has its own curvature
- Materials vary
- Stabilization design differs
- Lens thickness varies
Two brands with the same SPH/CYL/Axis can still feel and perform differently.
Your prescription may say:
Brand: Acuvue Oasys 1-Day for Astigmatism
or
Brand: Biofinity Toric
When ordering online, you must choose the brand listed unless your doctor approves a switch.
Putting the Numbers Together
Here’s a full toric prescription example:
SPH: –2.00
CYL: –1.25
Axis: 180
BC: 8.6
DIA: 14.5
Brand: Precision1 for Astigmatism
This means:
- Nearsighted by –2.00
- Astigmatism of –1.25 strength
- Astigmatism is horizontal (180°)
- Needs the fit of a specific brand
Why Toric Lens Prescriptions May Not Match Your Glasses Prescription
Your glasses prescription might show:
- –2.00 SPH
- –1.50 CYL
- 180 Axis
But your contact lens prescription might be:
- –1.75 SPH
- –1.25 CYL
- 180 Axis
- BC: 8.6
- DIA: 14.5
- Brand: MyDay Toric
This is normal because:
- Contacts sit directly on the eye
- Glasses sit 10–12 mm away
- Manufacturers offer preset CYL/Axis options
- Stabilization design affects fit
Contacts require a fitting — not just a copy of the glasses prescription.
How to Tell If You Need Toric Contact Lenses
You need toric lenses if:
✔ Your prescription includes CYL
✔ CYL is –0.50 or higher
✔ You have fluctuating clarity with regular lenses
✔ Your Axis is listed
✔ Your optometrist has recommended toric lenses
If your prescription says something like:
–2.25 / –0.75 × 180
You absolutely need toric lenses.
High Cylinder (High-CYL) Astigmatism
Many brands now offer CYL levels up to:
- –2.25
- –2.75
Some specialty brands go even higher.
People with high astigmatism benefit most from:
- Precision1
- MyDay
- Biofinity Toric XR
Understanding Stability & Rotation
Toric lenses must stay aligned.
If they rotate, vision instantly blurs.
Signs of rotation:
- Text looks “tilted”
- Vision is clear, then suddenly soft
- Clarity changes after blinking
Solutions:
- Try a different toric brand
- Adjust axis
- Choose daily lenses for better hydration
Reading Your Prescription When Buying Contact Lenses Online
You will need:
- Brand name
- Sphere (SPH)
- Cylinder (CYL)
- Axis
- Quantity (boxes per eye)
- Optional: Add-ons like shipping insurance
Online retailers will guide you through each dropdown.
Frequently Asked Questions
Can I use my glasses prescription for contacts?
No — you need a contact lens exam and fitting.
Why does my Axis change?
Your corneal shape can shift slightly over time.
Is a higher CYL worse?
It’s simply a stronger correction — not harmful.
My toric lenses blur sometimes — why?
Probably rotation or dryness. A different brand may fix it.
Do toric lenses cost more?
Yes. They require more complex manufacturing.
Conclusion
Understanding your astigmatism prescription is the key to choosing the right toric contact lenses. Once you know how SPH, CYL, Axis, BC, and DIA work, buying contacts online becomes simple and stress-free.