Eye prescriptions can be confusing, even if you’ve been wearing glasses for years. You might see a bunch of numbers, letters, and symbols on your prescription. What does it all mean? Don’t worry — glasses prescriptions are actually pretty simple. 39DollarGlasses is a doctor-founded and run company, so we’re here to translate your prescription and help you make sense of it all.

Let’s Start with the Eye Prescription Abbreviations

After your optometrist finishes your eye exam, they’ll write a prescription featuring abbreviations such as OD and DS. Prescription glasses makers called opticians rely on these abbreviations to understand what kind of lenses you need. You don’t have to memorize all these abbreviations, but understanding them can make reading your prescription easier.

• OD: The right eye. Most people need distinct prescriptions for each eye, so optometrists use this abbreviation to identify which eye needs which lens features.

• OS: The left eye. Optometrists use this abbreviation to label the prescription for your left eye.

- OU: Both eyes. Optometrists use this eye prescription abbreviation when both eyes need the same lens features.

• PD: Pupillary distance. This is the measurement between your pupils in millimeters. Opticians use this number to correctly position the prescription within your lenses. Some PD measurements have two numbers, such as 30/33. In this case, the first number is the distance from your right pupil to the bridge of your nose, while the second is the distance from your left pupil to the bridge of your nose. (Unfortunately, many optometrists don't include this measurement in prescriptions — but you can measure your PD at home using our simple PD guide.)

• NV: Near vision. This part of your prescription addresses your ability to see things up close.

• DV: Distance vision. This part of your prescription addresses your ability to see things far away.

• SPH: Sphere. Optometrists use the SPH section to explain how nearsighted or farsighted you are.

• PLANO: None (also written as PL, 0.00, or an infinity sign). If this abbreviation is in the SPH section of your prescription, it means you don’t need near vision correction or distance vision correction. However, you might still need glasses due to other vision problems, such as astigmatism.

• CYL: Cylinder. This part of your prescription addresses astigmatism, a common condition where the cornea in one or both eyes is misshapen.

• DS: Diopter sphere. Optometrists might include this abbreviation in the CYL section of your prescription. It means you don’t need correction for astigmatism. You may not require astigmatism correction in one or both eyes, but you may still need glasses due to other vision issues.

• AX: Axis. This eye prescription abbreviation is closely related to CYL. It helps opticians correctly position the CYL element in your lenses.

• ADD: Addition. Optometrists use this abbreviation if you need multifocal lenses, such as bifocals or progressives. It tells opticians how much magnifying power to include in the bottom half of your lenses.

• BVD: Back vertex distance. This is the distance between your corneas and the back of your lenses. It’s a relatively uncommon eye prescription abbreviation that’s usually used for very strong prescriptions to address the lenses’ effective strength. For example, if you wear lenses too close to your eyes, it might seem like the magnification is stronger than the actual prescription.

• PRISM: Prismatic power. This is a relatively uncommon eye prescription abbreviation. Optometrists include it in prescriptions for people with double vision.

Understanding the Eye Prescription Scale

Beyond abbreviations, your prescription may also have several numbers representing the eye prescription scale. Here’s a breakdown of what they mean and how the scale works.

Diopters: Numbers in the SPH or CYL Sections Any numbers you see in the SPH or CYL sections of your prescription represent diopters. A diopter is a unit of measure, like an inch or an ounce. But instead of measuring distance or weight, diopters measure how powerful your prescription is.

To understand how this works, we first need to explain focal length. Focal length is the distance at which your lenses bring objects into focus, measured in meters. For example, if you wear glasses with a 1-meter focal length (about 39 inches), an object that’s 1 meter in front of you will be clear and focused.

Diopters are the reciprocal of a lens's focal length. So if your glasses have a 1-meter focal length, the diopter measurement is 1. If your lenses have a ½-meter focal length, the diopter measurement is 2. Lenses with a ⅓-meter focal length have a diopter measurement of 3, and so on.

Nearsighted vs. Farsighted: Positive and Negative Diopters Importantly, diopters can be positive or negative on the eye prescription scale. Positive diopters indicate farsightedness, meaning things up close are blurry. Negative diopters indicate nearsightedness, meaning things further away are blurry.

People with perfect vision have the exact right amount of focusing power, so their lenses would have a diopter strength of 0. In contrast, people with nearsightedness have too much focusing power, so their lenses need to reduce that power using a negative lens, such as a diopter strength of -1. On the other hand, people with farsightedness don’t have enough focusing power, so their lenses need to increase that power using a positive lens, such as a diopter strength of +2.

Some prescriptions have both positive and negative numbers, while others don’t. Either way is normal. Eye care experts use the eye prescription scale to accurately customize your prescription, so you might see a blend of numbers depending on what you need to see clearly.

Eye Prescription Expiration Date

Eye prescriptions also include an expiration date. Most expire 1 year after your exam, but check your prescription for the most accurate information.

Eye prescriptions expire because your vision and eye health can change. Many people need new prescriptions to address increased nearsightedness or astigmatism, but your optometrist can also check for less common issues such as cataracts. Changes in eye health affect people of all ages, so it’s important to get a yearly exam to support healthy eyesight.

Common Eye Prescriptions

Eye prescriptions include specific information about your vision, but eye care professionals sometimes use umbrella terms to describe common eye prescriptions. Here’s what those terms mean. (Remember: these are just broad terms for common eye prescriptions. You should always use your prescription's specific details when ordering glasses.)

- Distance lenses - Distance lenses help you see things further away. If your prescription includes negative numbers in the SPH or CYL sections, you need distance lenses.

- Near-vision lenses - Near-vision lenses help you see things up close. If your prescription includes positive numbers in the SPH or CYL sections, you need near-vision lenses.

- Reading glasses - Reading glasses are similar to near-vision glasses — they help you see things up close. However, most people only wear reading glasses during up-close activities, like reading a book or using a computer, not all day.

- Single-vision glasses - Single-vision glasses have just one focal point, meaning they correct your vision at a fixed distance.

- Multifocal glasses - Multifocal glasses have more than one focal point. They might be bifocals, which include two distinct sections with different magnifying powers. Or they could be progressives, which gradually transition from less magnifying power at the top of the lens to more power at the bottom.

- Contacts - Contacts sit directly on your eyes. Glasses and contact prescriptions are not interchangeable, so you’ll need a separate prescription to wear contacts.

How Often Do Eye Prescriptions Change?

Eye prescriptions can stay the same for several years, but most people should get checkups annually to stay on top of any changes.

Age is typically the biggest factor contributing to prescription changes. Kids who wear glasses can experience significant changes yearly because their eyes are still growing. Similarly, middle-aged adults and seniors often need stronger prescriptions over time. With so many variables, yearly checkups are the best way to monitor your eye health and ensure your prescription is up-to-date.

Remember: You Have a Right to Your Eye Prescription

Since eye prescriptions are so important, you might be surprised that many optometrists won’t want to give you a copy. Usually, this is because the optometrist sells glasses and they don’t want you to shop elsewhere. You can buy glasses from your optometrist, but you don’t have to. You have a right to your prescription. Federal law requires optometrist’s offices to provide your prescription immediately after performing the exam, and the office can’t charge you a fee for a copy. Learn more about your eyeglasses prescription rights.

39DollarGlasses Is Here To Help

Eye prescriptions can be confusing, but 39DollarGlasses is here to help you understand what it all means. If you still have questions, contact our team of experts to learn more. We’re a doctor-run company, so we’re passionate about guiding you in all things eye health. Plus, we offer a variety of glasses styles at unbeatable prices. Use your prescription to order from 39DollarGlasses and get excerpt-made eyeglasses shipped straight to your door.