You’ve had your eye exam and received a prescription for colored contact lenses. But the numbers and abbreviations on that card can look confusing. Understanding your prescription ensures you order the correct lenses — and avoid discomfort or eye strain.
Here’s a simple breakdown of every term you’ll see.
The Prescription Format
A typical contact lens prescription includes information for each eye (often labeled OD and OS).
| Abbreviation | Meaning |
|---|---|
| OD | Oculus Dexter – right eye |
| OS | Oculus Sinister – left eye |
| OU | Oculus Uterque – both eyes |
Key Numbers Explained
1. Power (PWR or SPH)
This is the lens strength needed to correct nearsightedness or farsightedness.
- Negative number (e.g., -2.00) – Nearsighted (can’t see far)
- Positive number (e.g., +1.50) – Farsighted (can’t see near)
- 0.00 or Plano – No vision correction needed (common for colored lenses)
Range typically: -20.00 to +20.00 in 0.25 steps.
2. Base Curve (BC)
The curvature of the lens’s inner surface, measured in millimeters. Typical values: 8.3 – 8.9 mm.
- If the lens is too flat (higher BC), it moves too much.
- If too steep (lower BC), it fits too tightly.
Most colored lenses have a standard BC of 8.6 mm. Your prescription may say “8.6” or a range like “8.4–8.7.”
3. Diameter (DIA)
The total width of the lens, edge to edge, in millimeters. Typical values: 13.8 – 14.5 mm.
- Smaller DIA (13.8–14.0) – More natural, less enlargement.
- Larger DIA (14.2–14.5) – Noticeable widening effect.
4. Cylinder (CYL) and Axis (AX) – For Astigmatism
If you have astigmatism, you’ll see extra numbers:
- CYL – The amount of astigmatism correction (e.g., -0.75, -1.25, -2.25)
- AX – The orientation of the cylinder, from 0° to 180° (e.g., 90, 160, 20)
Not all colored lenses come in toric (astigmatism) versions. If you have significant astigmatism, ask your doctor for brands that offer colored toric lenses.
5. Addition (ADD) – For Presbyopia
If you need multifocal or bifocal correction (typically age 40+), you’ll see an ADD value, usually +0.50 to +3.00. Colored multifocal lenses are rare but exist.
Sample Prescription
Here’s what a real prescription might look like:
| OD (Right) | OS (Left) | |
|---|---|---|
| Power (PWR) | -2.00 | -1.75 |
| Base Curve (BC) | 8.6 | 8.6 |
| Diameter (DIA) | 14.2 | 14.2 |
This person is mildly nearsighted, with the same BC and DIA for both eyes.
What If You Want Colored Lenses That Don’t Match Exactly?
Many popular colored lenses are only made in one BC (usually 8.6 mm) and one DIA (14.0–14.2 mm). If your prescribed BC is 8.4 or 8.7, some doctors say a 0.2 mm difference is acceptable because soft lenses flex slightly. But always ask your eye doctor first — do not assume.
For power, you can usually round to the nearest available step (e.g., -2.00 if your prescription is -1.90). Never change cylinder or axis on your own.
Why You Cannot Use a Glasses Prescription for Contacts
A glasses prescription sits 12 mm away from your eyes. A contact lens sits directly on your cornea. The power is different — especially for higher prescriptions or astigmatism. Always get a contact lens specific prescription.
Prescription Expiration
In most countries, contact lens prescriptions expire after 1–2 years. After that, you need a new eye exam. Wearing lenses with an expired prescription (even if the lenses are unopened) is not recommended — your eyes may have changed.
Quick Reference Card
| Symbol | Meaning | Typical Range |
|---|---|---|
| PWR / SPH | Correction power | -20 to +20 |
| BC | Base curve (fit) | 8.3 – 8.9 mm |
| DIA | Diameter (size) | 13.8 – 14.5 mm |
| CYL | Astigmatism correction | -0.25 to -2.75 |
| AX | Cylinder orientation | 0° – 180° |
| ADD | Multifocal addition | +0.50 to +3.00 |
The Bottom Line
Reading your colored contact lens prescription is easy once you know the terms. Focus on Power, BC, and DIA for most colored lenses. If you have astigmatism, you’ll need toric colored lenses — fewer options exist, so plan ahead. Keep your prescription current, and never borrow someone else’s. When in doubt, ask your eye doctor or optician to help you order.
Disclaimer: This guide is for educational purposes. Always follow the exact prescription provided by your licensed eye care professional.