How to Read Your Eye Prescription and Understand the Numbers
Your eyeglass prescription can look confusing at first, full of abbreviations, plus and minus signs, and numbers that don't seem to mean much on their own. Each part of it tells your optician how to build lenses that correct your vision.
A better understanding of these numbers can help you feel more informed when you choose new glasses or talk through changes in your vision with your eye doctor.
A plain-language tour of the numbers on your eyeglass prescription, from SPH and CYL to AXIS, ADD and PD, and what each one says about the correction your eyes need.
Common Vision Problems That Require Prescription Glasses
Eyeglass prescriptions correct refractive errors, which occur when light doesn't focus properly on the retina at the back of your eye. These conditions affect how clearly you see at different distances.
Nearsightedness (Myopia)
Myopia makes distant objects appear blurry while nearby objects usually stay clear. It occurs when light focuses in front of the retina rather than directly on it.
Farsightedness (Hyperopia)
Hyperopia can make nearby objects difficult to focus on, although distance vision may also be affected. Some people notice headaches or eye strain, particularly during reading or other close-up tasks.
Astigmatism
Astigmatism occurs when the cornea or lens has an uneven curvature, causing blurry or distorted vision at both near and far distances. It can occur alongside nearsightedness or farsightedness.
Presbyopia
Presbyopia is an age-related change in the eye's ability to focus on nearby objects. It typically becomes noticeable after age 40 and may make it harder to read small print or view your phone.
Unlike hyperopia, presbyopia develops as the eye's natural lens becomes less flexible with age. Reading glasses, bifocals, or progressive lenses can help correct near vision.
What the Numbers on Your Eye Prescription Mean
Your prescription uses measurements called diopters (D) to describe the lens power needed to correct your vision. Generally, the farther a sphere or cylinder value is from zero, the stronger that part of your prescription.
Your right and left eyes may have different prescriptions, which is completely normal.
A prescription might look like this:
| Eye | SPH | CYL | AXIS |
|---|---|---|---|
| OD | -4.00 | -1.50 | 180 |
| OS | +0.50 |
Each column describes a different part of your vision correction.
OD and OS: Your Right and Left Eyes
OD stands for oculus dexter, the Latin term for the right eye, while OS stands for oculus sinister, meaning the left eye.
Some prescriptions also use OU, or oculus uterque, to refer to both eyes.
SPH (Sphere): Nearsightedness and Farsightedness
The SPH value indicates the lens power needed to correct nearsightedness or farsightedness.
A minus sign (-) indicates a prescription for nearsightedness, while a plus sign (+) indicates farsightedness.
For example, a prescription of -4.00 indicates more nearsighted correction than -1.00. A prescription of +2.00 indicates more farsighted correction than +0.50.
CYL (Cylinder): The Amount of Astigmatism
The CYL value measures the lens power needed to correct astigmatism.
This number may appear with a plus or minus sign, depending on how your eye doctor writes the prescription. A larger absolute value generally indicates a greater amount of astigmatism correction.
If the CYL field is blank, your prescription doesn't include a cylinder correction.
AXIS: The Direction of Astigmatism Correction
The axis indicates the orientation of the cylindrical correction needed for astigmatism. It's measured in degrees from 1 to 180.
The axis doesn't describe how strong your prescription is. Instead, it tells the optician how to position the astigmatism correction within your lenses.
An axis value is typically included only when your prescription has a CYL measurement.
Other Abbreviations You May See on Your Prescription
Some prescriptions include additional measurements depending on your vision needs and the type of glasses you're getting. Here are the ones you're most likely to run into:
- OD / OS / OU: your right eye, left eye, or both eyes together.
- SPH: sphere, the lens power that corrects nearsightedness or farsightedness.
- CYL: cylinder, the lens power that corrects astigmatism.
- AXIS: the 1 to 180 degree direction of the astigmatism correction.
- ADD: extra lens power for reading and other close work.
- PD: pupillary distance, in millimeters, used to center your lenses.
ADD: Extra Magnification for Reading
ADD stands for additional lens power. It's commonly used in prescriptions for bifocals, progressive lenses, and certain reading glasses.
This value is usually written as a positive number and indicates the extra power needed for near vision.
For example, an ADD value of +2.00 means your near-vision lens power includes an additional 2.00 diopters beyond the distance prescription.
PD: Pupillary Distance
Pupillary distance (PD) measures the distance between the centers of your pupils, usually in millimeters.
This measurement helps position the optical centers of your lenses correctly in front of your eyes. Your optician may measure it separately during your eyewear fitting, so it doesn't always appear on your prescription.
DV and NV: Distance and Near Vision
DV stands for distance vision, while NV stands for near vision.
These abbreviations help distinguish prescriptions for activities like driving and watching television from those for reading or other close-up tasks.
Why Your Eye Prescription May Change Over Time
Your prescription can change as you age or as your eyes develop. Nearsightedness may progress during childhood and adolescence, while presbyopia commonly affects near vision beginning in middle age.
A prescription change doesn't always mean something is wrong with your eye health. However, persistent blurry vision, headaches, or difficulty focusing may indicate that your current glasses no longer meet your needs.
Regular eye exams allow your eye doctor to check your prescription and assess your eye health. Sudden vision changes, particularly those accompanied by eye pain, flashes of light, or new floaters, require prompt medical attention.
When it's time for new lenses, the eyeglasses and lens options at our Brookings optical can put an updated prescription into frames that suit your day.
Understand Your Vision at 20/20 FAMILY VISION
Your eye prescription includes information about how your eyes focus and the correction you need. An accurate prescription and properly fitted lenses can help you see comfortably throughout your day.
At 20/20 FAMILY VISION in Brookings, SD, our team can assess your vision, explain your prescription, and help you understand your eyewear options.
Contact 20/20 FAMILY VISION at 605-692-2020 to schedule a comprehensive eye exam and get answers to your questions about your vision.
