Decoding Your Astigmatism Prescription in 5 Minutes (What are CYL & AXIS?)

"Does this eye prescription look like a secret code? Worried you'll enter the wrong numbers and mess up your order?"

When you try to order toric (astigmatism) contact lenses online, it's easy to feel lost with unfamiliar terms like SPH, CYL, and AXIS. We've all been there.

But don't worry! By the end of this article, you'll be able to decode the important information about your eyes and order your perfect lenses with total confidence.

1. The Basics of Every Prescription: SPH, OD, & OS

Let's start with the most basic terms. If you know these, you're halfway there.

• SPH (Sphere):
  This is your main prescription power, often just called "power." A minus sign (-) indicates nearsightedness (myopia), while a plus sign (+) indicates farsightedness (hyperopia). The higher the number, the stronger the prescription.
  

  Example: "-2.50" means a standard level of nearsightedness.



• OD (Oculus Dexter):
  This is Latin for "Right Eye." Any information on the OD row is for your right eye.


• OS (Oculus Sinister):
  This is Latin for "Left Eye." Any information on the OS row is for your left eye.

💡 Quick Tip: If you get OD and OS mixed up, just remember that you "left" something "sinister" behind. It's a bit dark, but it works!

2. The Heart of Astigmatism: CYL & AXIS

Now for the key part: astigmatism. If you don't have astigmatism, this section on your prescription will be blank.

• CYL (Cylinder):
  This indicates the "amount" of astigmatism you have. It's always a minus (-) number, and the higher the number, the more significant your astigmatism is.
  

  Example: "-1.25" indicates a moderate amount of astigmatism.

  
  

  
  

  Choosing the correct CYL value is the first step to getting sharp, clear vision.

• AXIS:
  This indicates the "direction" or "orientation" of your astigmatism. It's a number between 0 and 180 degrees. Think of it as the angle where vision correction is needed on the lens.
  

  Example: "180" or "90" refers to the angle of the correction.

  
  

  
  

  【IMPORTANT】 Even a slight error in the AXIS can cause blurry vision. The values are typically in steps of 10, so never change the number on your prescription and always enter it exactly as written.

3. Let's Decode a Sample Prescription

Let's imagine you received the following prescription:

	SPH	CYL	AXIS
OD (Right)	-3.00	-0.75	180
OS (Left)	-3.25	-1.25	90

How do we interpret this?

• Right Eye (OD):
  Has a nearsightedness of -3.00 diopters, an astigmatism of -0.75 diopters, and a correction axis of 180 degrees.


• Left Eye (OS):
  Has a nearsightedness of -3.25 diopters, a slightly stronger astigmatism of -1.25 diopters, and a correction axis of 90 degrees.



Now you can confidently select the correct SPH, CYL, and AXIS values for each eye when ordering online!

4. Final Important Reminders

• Glasses and contact lens prescriptions can be different. Because contacts sit directly on your eye, the power can differ from your glasses prescription. Always use a prescription specifically for contact lenses.


• Keep your prescription up to date. Your vision can change, so it's best to visit your eye doctor at least once a year for a new check-up.


• If you want to dive deeper or read more medical details, referring to information from experts is always a great idea.

Learn More: "What Is Astigmatism?" - Check out this professional resource from the American Academy of Ophthalmology.
What Is Astigmatism? - American Academy of Ophthalmology



• No more hesitation in front of those confusing terms. Understanding your prescription is the first step to a clearer, more comfortable world.
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