How to Read Your Eye Prescription for Glasses or Contacts
While it may look like a foreign language, your glasses or contacts prescription contains simple information describing exactly how your new glasses should be made or specifies which contacts are right for you. Understanding how to read your eye prescription is a simple way to be more involved in your eye care and better understand eye health.
Vision Prescription Abbreviations & Terms, Explained
Your glasses or contacts prescription contains a series of abbreviations and numbers that summarize your vision correction needs. Opticians read these numbers and use them to select or create lenses tailored to your vision requirements. Let's review the prescription information and what it says about your eyes.
OD and SD
These abbreviations specify which eye should receive which corrections. While some optometrists might specify "RE" and "LE" for the right eye and left eye, traditional prescriptions use the original Latin "OD" and "OS". OD stands for "oculus dexter", which is the right eye. OS stands for "oculus sinister", or the left eye.
If both eyes need the same prescription, you'll sometimes see "OU", which stands for "oculus uterque", meaning both eyes.
S, SPH or Sphere
The markings S, SPH or Sphere refer to the amount of nearsightedness or farsightedness you have. You'll see a number with a plus sign (+) or a minus sign (-) next to these letters. A number with a plus sign means the eye is farsighted, while a minus sign means nearsighted.
The number itself measures how much correction you require, using a unit of measure called diopters. The farther from zero, the stronger the prescription. A zero (or a "PL" or "Plane") means that no correction is necessary for that eye.
Are you curious about what the diopter value on your prescription means?
- Myopia (-): 0.00 to -3.00 is mild, -3.00 to -6.00 is moderate and -6.00 or more is high.
- Hyperopia (+): 0.00 to 2.25 is mild, 2.25 to 5.00 is moderate and 5.00 or more is high.
C or Cylinder
This number indicates the level of astigmatism for each eye. Astigmatism means that, like most people, your eyeball is not perfectly round. Pronounced astigmatism can result in blurry vision that requires correction. If you don't need astigmatism correction, you may not see this number on the prescription.
Like Sphere, Cylinder is a number with a plus or minus sign. The larger the number, the more notable your astigmatism: 0.00 to 1.00 is mild, 1.00 to 3.00 is moderate and any value over 3.00 is considered severe.
Axis
If your prescription contains astigmatism correction, you may also see a number for "Axis." This number specifies where the astigmatism is located on the eye so the lens adjustment can be placed correctly on the lens. The Axis value ranges from 0 to 180.
Add
For bi-focal and progressive lenses, "Add" specifies how much magnifying power to add to the bottom of the lens to correct your vision for viewing nearby objects. For example, if the prescription is for +1.00, and you have an Add of +2.00, the nearsighted portion of the lens is set to +3.00. This number is always positive, so you probably won't see a plus sign next to the number. Usually, both eyes have the same Add value—ranging from .75 to 3.00.
Prism
For conditions resulting in double vision, you may see one more number on the prescription called "Prism". This number and a description like "base up" or "base down" specify how the prism lens should be oriented to correct for double vision.
Differences Between Glasses and Contact Lens Prescriptions
Now that you know the meaning of the common terminology and numbers on your prescription, reading it is simple. However, there is a little more to learn. Prescription types differ: glasses and contacts work in distinctly different ways because of how they are placed relative to the surface of the eye.
Let's take a look at each.
Glasses for Vision Correction
Because glasses rest away from the eyes, they can support specialized features like prism correction, so all the values listed above are applicable to glasses prescriptions. Unlike contact lenses, measures of fit and feel don't appear on glasses prescriptions. How your glasses fit and feel is up to you. You select frames to match your style preferences and achieve a comfortable fit on your face.
Proper Contact Lens Fitting
Contact lenses rest directly on the eyes, requiring a few additional specifications to ensure a proper fit.
Base Curve
The base curve is a measure of the curvature of the eye. The correct base curve ensures the lens lies snugly across the eye surface.
Diameter
The diameter is the size of the lens. A specified diameter ensures you get a lens that's neither too large nor too small to fit correctly on your eye.
Lens Material
This specification indicates the lens type. Manufacturers make contact lenses from different hydrogels, each with a unique fit and feel. For example, some are more breathable and support long-time wear, while others are designed for one-day use.
Brand/Manufacturer
Most contact lens prescriptions, unlike eyeglass prescriptions, specify a brand or lens manufacturer. Your eye doctor recommends the best brand or manufacturer for you.
Can You Have a "Bad" Vision Prescription?
You may wonder if you can tell how bad vision is based on the prescription. When you see higher numbers on a prescription, your first instinct may be to think it’s a "bad prescription". In truth, there’s no such thing as a good or bad prescription.
Just like everyone has a different type of hair that requires specific products or care regimens, everyone has different eyes that result in unique vision prescriptions. You shouldn't compare your prescription to others, even if the numbers are higher than those who also wear glasses. Your prescription will be good for you, and that’s all that matters.
Still, three categories of prescriptions help eye doctors classify the prescription strength for nearsightedness or farsightedness. These categories help them understand what type of prescription you have. The categories are as follows:
- Mild: Between 0.25 to 2.00
- Moderate: Between 2.25 and 5.00
- Severe: More than 5.00
Can You Calculate Visual Acuity from a Lens Prescription?
Visual acuity measures how well your eyes can see shapes and details. An eye doctor can test visual acuity both with and without you wearing corrective lenses. A visual acuity test scores your ability to see at a certain distance. It will look like 20/20 or 20/40.
All prescriptions aim to achieve an average sight score of 20/20. You can’t always determine your visual acuity simply by looking at the prescription. Still, after you get glasses in the new prescription, you can test them and ensure your score has increased.
Where to Find Your Vision Prescription
Our eyes continually change, even without our noticing, so you should visit the eye doctor annually. If you need an updated vision prescription, it’s easy to get one. Start by making an appointment with an eye doctor!
At the end of your appointment, the doctor presents you with a new, updated prescription. If you’ve lost that prescription information but recently had your eyes tested, your eye doctor should have the prescription on file. Just call and request it.
Understanding Your Glasses or Contacts Prescription
Reading your contact lens or eyeglass prescription is simple once you understand a few values and what they mean. With this knowledge, you can partner with your eye doctor to ensure optimal vision. Schedule an appointment with a licensed optometrist at Visionworks today!
Information received through Visionworks® content is for informational purposes only and does not constitute medical advice, medical recommendations, diagnosis, or treatment. Always seek the advice of your eye doctor, physician, or other qualified health provider with any questions you may have regarding a medical condition.
Claims regarding blue light efficiency are supported by manufacturer-provided test results.
