How to Read Your Prescription?
Mar 03,2025 | Y
Decoding your eye prescription is key to finding the perfect colored contact lenses. This guide breaks down terms like OD, OS, Sphere, Cylinder, and Axis, helping you choose lenses that enhance your look while meeting your vision needs.
OD and OS: What Do They Mean?
When you first look at your eye prescription, you might notice the abbreviations OD and OS instead of “right eye” and “left eye.” These terms come from Latin and are commonly used in optometry:
- OD (Oculus Dexter): Refers to your right eye.
- OS (Oculus Sinister): Refers to your left eye.
- Occasionally, you may also see OU (Oculus Uterque), which refers to both eyes.
The Three Main Components of Your Prescription
Your prescription provides detailed information about the correction your eyes need. It typically includes three main components: Sphere (SPH), Cylinder (CYL), and Axis. Here’s what each one means:
1. Sphere (SPH)
The Sphere indicates the lens power needed to correct nearsightedness or farsightedness:
- A negative number (e.g., -2.50) means you are nearsighted (difficulty seeing far away).
- A positive number (e.g., +1.75) means you are farsighted (difficulty seeing up close).
This power is consistent across the entire lens.
2. Cylinder (CYL)
The Cylinder is used to correct astigmatism, which occurs when the cornea or lens of your eye has an irregular shape. Unlike the Sphere, the Cylinder adjusts specific areas of the lens to address these irregularities.
3. Axis
The Axis is a number between 0° and 180° that indicates the orientation of the cylindrical correction. It ensures the lens is positioned correctly to align with your eye’s shape and correct astigmatism.
Glasses vs. Contact Lenses: Adjusting Your Prescription
If you’re switching from glasses to contact lenses, your prescription might need adjustments. Contact lenses sit directly on the surface of your eye, unlike glasses, which are positioned a short distance away. This difference affects the lens power required for clear vision.
Here’s a general adjustment chart for converting glasses prescriptions to contact lens prescriptions:
| Glasses Prescription | Contact Lens Adjustment |
| ≤-4.00 | No adjustment needed |
| ≤-5.00 | Subtract 0.25 |
| ≤-7.00 | Subtract 0.50 |
| ≤-8.00 | Subtract 0.75 |
| ≤-9.00 | Subtract 1.00 |
| ≤-10.00 | Subtract 1.25 |
| ≤-11.00 | Subtract 1.50 |
| ≤-12.00 | Subtract 1.75 |
Tips for Use:
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Reference Only: This chart is for general guidance. Always consult your optometrist or eye care professional for an accurate prescription.
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Choose Closest Match: If the calculated contact lens prescription doesn’t match an available option, select the closest available power.
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Personal Adjustments: Individual factors like astigmatism or eye curvature may require further adjustments.
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Consult a Professional: Always confirm your prescription with an optometrist for accuracy.
How to Adjust Contact Lens Prescription for Astigmatism?
Formula: Recommended Contact Lens Power = Original SPH + (CYL ÷ 2)
Example Calculation
| Original Prescription | SPH (Spherical Power) | CYL (Astigmatism) | Recommended Prescription |
|---|---|---|---|
| Right Eye (OD) | -1.50 | -0.50 | -1.75 |
| Left Eye (OS) | -2.00 | -1.00 | -2.50 |
Calculation Process:
- Right Eye (OD): -1.50 + (-0.50 ÷ 2) = -1.75
- Left Eye (OS): -2.00 + (-1.00 ÷ 2) = -2.50
Important Notes
- If your astigmatism (CYL) is greater than -2.00, we recommend using specialized Toric lenses for better vision correction.
- We currently do not offer Toric lenses. If you have high astigmatism, please consult your optometrist for professional advice.
- This method is only suitable for mild astigmatism and should be used under the guidance of a professional optometrist.
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