Have you ever looked at your eyeglass prescription and thought, “What do all these numbers mean?” Don’t worry—you’re not alone! Eyewear prescriptions may seem like a secret code, but once you break it down, it’s actually pretty straightforward.
In this blog, we’ll explain what those numbers and abbreviations mean, how your prescription may change over time, and how glasses and contact lens prescriptions differ. We’ll even help troubleshoot common issues, so you always get the clearest, most comfortable vision possible.
Understanding Your Eyeglass Prescription
A typical eyeglass prescription will include a table with abbreviations like SPH, CYL, AXIS, and ADD. Here’s what each means:
SPH (Sphere)
What it means: The amount of correction (in diopters) needed for nearsightedness or farsightedness.
- Negative (-) values: You’re nearsighted (can see close-up, but not far away)
- Positive (+) values: You’re farsighted (can see far away, but not close-up)
Example:SPH: -2.50 means you need a -2.50 diopter lens to correct distance vision.
CYL (Cylinder)
What it means: This corrects astigmatism, which is when the cornea is shaped more like a football than a basketball, causing blurry or distorted vision.
- Can be positive (+) or negative (-)
- If this field is blank, you probably don’t have astigmatism
Example:CYL: -1.00 indicates mild astigmatism correction is needed.
AXIS
What it means: The angle (from 0° to 180°) at which the astigmatism correction should be applied. It works in conjunction with CYL.
Example:AXIS: 90 means the astigmatism correction is applied vertically.
ADD
What it means: The additional magnifying power needed for reading or close-up vision, typically for people with presbyopia (age-related near vision loss).
- Commonly found in progressive, bifocal, or reading prescriptions
- Always a positive (+) number
Example:ADD: +2.00 provides +2 diopters of magnification for near tasks like reading.
Other Notations You Might See:
- OD = Right eye (from Latin oculus dexter)
- OS = Left eye (oculus sinister)
- OU = Both eyes (oculus uterque)
- PD = Pupillary Distance – the space between the centers of your pupils, used to align lenses accurately
How Prescriptions Change with Age
It’s perfectly normal for your vision to evolve over time. Here’s how your prescription may change with age:
Children (0–18)
- Vision is still developing
- Myopia (nearsightedness) may progress rapidly, especially during growth spurts
- Regular checkups are critical to monitor changes
Adults (18–40)
- Vision tends to stabilize, but screen strain or long hours at a computer may cause eye fatigue
- Astigmatism may develop or worsen subtly
Middle Age (40–60)
- Presbyopia usually begins around age 40
- You may notice you’re holding books farther away or need reading glasses
- Many people switch to bifocals or progressives during this stage
Seniors (60+)
- Higher risk of age-related eye diseases like cataracts, glaucoma, and macular degeneration
- Prescription changes may become more frequent
- Regular comprehensive eye exams are essential
Glasses vs. Contact Lens Prescriptions: What’s the Difference?
You can’t use your glasses prescription to order contacts—and vice versa. Here’s why:
| Feature | Glasses Prescription | Contact Lens Prescription |
|---|---|---|
| Distance from Eye | Lenses sit about 12mm from your eyes | Lenses sit directly on the cornea |
| Includes | SPH, CYL, AXIS, ADD | SPH, CYL, AXIS, ADD + Base Curve (BC), Diameter (DIA), Brand |
| Fitting | One size fits all | Must match corneal shape and size |
| Brand Specific? | No | Yes — contact lenses must match FDA-approved brands and fits |
Your optometrist must measure your eye’s curvature to determine the right base curve and diameter for your contacts. Wearing the wrong size can lead to discomfort or eye health issues.
Troubleshooting Common Prescription Issues
Experiencing discomfort or blurry vision even with new glasses or contacts? Here are some common issues and what to do:
1. Headaches or Eye Strain
Cause: Incorrect prescription, frame misalignment, or wrong pupillary distance
Fix: Return to your eye doctor for a re-check. Adjust frame fit or prescription as needed.
2. Blurry Vision with New Glasses
Cause: Normal adjustment period (especially with progressives or new prescriptions)
Fix: Give it 1–2 weeks. If it doesn’t improve, consult your optometrist.
3. Dizziness or Depth Perception Issues
Cause: Often due to switching to multifocal lenses or a big prescription jump
Fix: Try gradual wear, especially in the first few days. If symptoms persist, your optician may adjust the lens position.
4. Dry or Irritated Eyes with Contacts
Cause: Lens fit issues, dryness, overwear
Fix: Use rewetting drops, take breaks, or switch to daily lenses. Visit your doctor if discomfort continues.
5. One Eye Sees Sharper Than the Other
Cause: PD misalignment, prescription mismatch between lenses
Fix: Return the glasses to your provider for measurement verification and lens recheck
Final Thoughts
Your eyeglass or contact lens prescription is more than just numbers—it’s a detailed formula customized to give you the best vision possible. Understanding it helps you make smarter eyewear choices, recognize when something feels off, and know what changes to expect over time.
Need help interpreting your current prescription or choosing the right glasses or contacts? Schedule an eye exam with your optometrist, or visit us for expert guidance on fit, style, and comfort.