How to Read Your Eyeglass Prescription Like a Pro
After an eye exam, you’re often handed a small slip of paper filled with a grid of numbers and abbreviations that can look like a secret code. Understanding this document is the first step toward seeing the world more clearly and feeling confident about your eyewear choices. This guide will help you decipher the terms on your eyeglass prescription, turning that complex chart into simple, useful information.
First, you'll notice the abbreviations OD, OS, and sometimes OU. These are Latin terms that opticians use to differentiate between your eyes: OD (Oculus Dexter) refers to your right eye, and OS (Oculus Sinister) refers to your left eye. If you see OU (Oculus Uterque), it simply means something applies to both of your eyes. This is the basic map that tells you which information belongs to which eye.
The first number you’ll likely see is under the heading SPH (Sphere). This indicates the main strength of the lens, measured in units called diopters, required to correct your vision. A minus sign (-) before the number means you are nearsighted (myopia), making it difficult to see distant objects clearly. A plus sign (+) indicates you are farsighted (hyperopia), which means you have trouble focusing on objects up close. The further the number is from zero, the stronger your prescription is.
If you have numbers in the CYL (Cylinder) and Axis columns, it means you have an astigmatism, a very common condition where the cornea has an irregular shape that causes blurred vision at all distances. These two values always work together. The CYL number indicates the lens power needed to correct the astigmatism, while the Axis is a number between 1 and 180 that tells the lab the precise orientation of that correction in your lens. If these columns are blank, you likely have little to no astigmatism.
For those who need help with near vision, the ADD (Addition) value is key. This number is found on prescriptions for multifocal lenses, like bifocals or progressives, and represents the added magnifying power in the lower part of the lens for reading. It addresses presbyopia, the natural, age-related loss of near-focusing ability. The ADD value is always a positive number and is typically the same for both eyes.
Finally, a crucial measurement for crafting your glasses is the PD (Pupillary Distance). This is the distance in millimeters between the centers of your pupils. An accurate PD ensures the optical center of your lenses aligns perfectly with your eyes, which is essential for clear and comfortable vision, a key component in understanding your prescription. This measurement may be on your prescription, but it is often taken by an optician when you are being fitted for your frames.
Understanding your prescription empowers you to be an active participant in your eye health. While this guide covers the basics, our knowledgeable opticians are always here to answer your questions. We can help you choose the perfect frames and lenses to match your prescription, needs, and lifestyle. Ready to turn that piece of paper into a new way of seeing? Book your appointment with us today and let our experts guide you through the process.
