How to Read Your Eye Prescription: A Detailed Guide

Understanding your eye prescription is essential when ordering glasses or contact lenses online. If you've ever looked at your prescription and felt confused by the abbreviations and numbers, don’t worry—you’re not alone! This guide will help you decode your prescription so you can order the right eyewear with confidence.

What’s on an Eye Prescription?

A standard eye prescription includes several measurements that determine the corrective power your lenses need. Here’s a breakdown of the key terms you’ll see:

1. OD & OS (Right & Left Eye)

• OD (Oculus Dexter) → Refers to your right eye
• OS (Oculus Sinister) → Refers to your left eye
• Some prescriptions also include OU (Oculus Uterque), meaning both eyes.

2. SPH (Sphere) – Nearsightedness or Farsightedness

The Sphere (SPH) number indicates the lens power needed to correct your vision:

• Negative (-) values → You are nearsighted (myopia), meaning distant objects appear blurry.
• Positive (+) values → You are farsighted (hyperopia), meaning close-up objects appear blurry.
• Measured in diopters (D). The further from zero, the stronger the prescription.

3. CYL (Cylinder) & Axis – Astigmatism Correction

If you have astigmatism, your cornea is irregularly shaped, causing blurry or distorted vision. The Cylinder (CYL) and Axis correct this issue.

• CYL (Cylinder) → Measures the degree of astigmatism. A negative (-) or positive (+) value indicates the level of correction needed.
• Axis → Ranges from 1 to 180 degrees and indicates the orientation of the correction needed for astigmatism.

💡 If there's no CYL or Axis in your prescription, you likely don’t have astigmatism.

4. ADD (Addition) – Presbyopia & Multifocal Lenses

• The ADD value is for those needing bifocals, progressive lenses, or reading glasses.
• It represents the additional magnifying power required for close-up vision.
• The value is usually positive (+) and ranges from +0.75 to +3.50 D.

5. PD (Pupillary Distance) – Lens Alignment

• PD (Pupillary Distance) measures the distance (in millimeters) between the centers of your pupils.
• It ensures your lenses are aligned correctly with your eyes for clear vision.
• PD can be written as one number (e.g., 63 mm) or two numbers (e.g., 31/32 mm, indicating right and left eye separately).

6. Prism & Base – Eye Alignment Issues

• Prism corrects eye alignment issues like strabismus (crossed eyes) or double vision.
• Base direction (up, down, in, out) indicates how the prism correction is applied.
• If you don’t have these values, your vision does not require prism correction.

Example of an Eye Prescription

• This person is nearsighted with astigmatism in both eyes.
• They need progressive or bifocal lenses with an ADD value of +2.00.
• Their total PD is 63 mm (31+32).

How to Use Your Prescription for Buying Glasses Online

Once you understand your prescription, you can easily enter the details when ordering eyeglasses online. Here's what to do:

✅ Check if your prescription is up to date (valid within 1–2 years).
✅ Input SPH, CYL, Axis, and ADD values exactly as written.
✅ Measure PD accurately or ask your optometrist for confirmation.
✅ Select the right lenses (single vision, bifocal, progressive, blue light, etc.).

Common Questions About Eye Prescriptions

1. Can I use my eyeglass prescription for contact lenses?

No, a contact lens prescription is different from an eyeglass prescription because it includes additional measurements like base curve (BC) and diameter (DIA).

2. What if my prescription only has SPH and no CYL or Axis?

That means you don’t have astigmatism, and you only need basic spherical correction for nearsightedness or farsightedness.

3. How do I measure my PD at home?

You can use a ruler and a mirror or an online PD measurement tool. Place the ruler over your nose and measure the distance between your pupils in millimeters.

Reading your eye prescription might seem confusing at first, but once you understand the key terms, you’ll have no trouble ordering the correct glasses. If you’re unsure about any details, consult your eye doctor or reach out to your eyewear provider for assistance.

Ready to Order?

Now that you know how to read your prescription, you can confidently buy glasses online from TrendingSpecs.com or your favorite eyewear store!