How to Read and Understand Your Glasses Prescription

When you walk out of your eye doctor's office with a new glasses prescription, you are handed a sheet of paper covered in abbreviations, grid columns, and numbers with plus and minus signs. It can look like a foreign language.

Understanding your prescription empowers you to make better choices when shopping for frames and lenses. Let’s break down what each abbreviation and number means.

1. The Latin Basics: OD vs. OS vs. OU

First, you will notice rows labeled with OD, OS, or sometimes OU. These are Latin abbreviations eye care professionals use to refer to your eyes:

• OD (Oculus Dexter): Your Right Eye.
• OS (Oculus Sinister): Your Left Eye.
• OU (Oculus Uterque): Both Eyes (used if both eyes share the exact same prescription).

2. SPH (Sphere): Your Primary Vision Correction

The Sphere (SPH) column indicates the primary strength of your lens. It measures how strong your nearsightedness or farsightedness correction needs to be.

• Minus sign (-): You are nearsighted (myopia), meaning you have trouble seeing things in the distance.
• Plus sign (+): You are farsighted (hyperopia), meaning you have trouble focusing on objects up close.
• The Numbers: Sphere is measured in diopters. A number like -1.00 is a mild prescription, while -6.00 is a strong prescription.

3. CYL (Cylinder) and AXIS: Astigmatism Correction

If you have astigmatism (which means your cornea is shaped more like a football than a basketball), you will see numbers in these two columns. If you don't have astigmatism, these will be blank.

• CYL (Cylinder): Measures the strength of the astigmatism correction. Like Sphere, it can be positive or negative.
• AXIS: Measured in degrees (from 1 to 180). This doesn't indicate lens power; instead, it specifies the exact angle at which the cylinder correction needs to sit in your frame to correct your astigmatism.

4. ADD: Reading & Multifocal Correction

If you are over 40 and experiencing presbyopia (natural aging of the eyes making close-up reading difficult), you will have a number in the ADD column.

• What it does: It stands for "addition" and specifies the additional magnifying power needed at the bottom of the lens for reading.
• Application: This number is always positive (+) and is used for reading glasses, bifocals, or progressive lenses.

5. PD (Pupillary Distance)

Your Pupillary Distance (PD) is the distance in millimeters between the centers of your pupils. It ensures the optical center of your lenses sits exactly in front of your pupils.

• Why it matters: Even if the rest of your prescription numbers are typed perfectly, if your PD is off, you will experience eye strain, headaches, and blurred vision.
• Checking your Rx: Some doctors write this on your prescription, while others measure it during your frame fitting. Learn how to get yours by checking out How to Request Your PD Measurement.

Summary Table of Abbreviations

• OD: Right Eye
• OS: Left Eye
• SPH: Sphere (Nearsighted / Farsighted)
• CYL: Cylinder (Astigmatism strength)
• AXIS: Direction of astigmatism correction (1 to 180 degrees)
• ADD: Near magnification power for multifocals
• PD: Pupillary Distance (lens centering)
• PRISM: Prism correction (for eye alignment issues)