Regular eye exams are an important part of keeping your eyes healthy and your vision sharp.
At your eye exam, an eye doctor, optometrist, or ophthalmologist, will check for any signs of eye disease. If your vision needs to be corrected, you’ll be given a prescription for eyeglasses or contact lenses.
Eye prescriptions can be hard to decipher, though. They usually contain an assortment of numbers and letters that can be confusing if you don’t know what they mean.
This article will help make sense of the abbreviations and numbers that may be included in your eye prescription. It will also explain how prescriptions can vary depending on your vision issue.
Your eyeglass or contact lens prescription will contain various abbreviations, many of which will be followed by numbers.
Here’s a summary of what these abbreviations mean:
A glossary of eye prescription abbreviations
- ADD stands for the additional lens power needed to make it easier for you to read. This number is seen on prescriptions for reading glasses or the lower portion of bifocal or progressive lenses.
- Axis is a number between 1 and 180. It indicates exactly where the astigmatism appears on your eye.
- BO, BI, BU, BD stand for base out, base in, base up, and base down. These abbreviations tell the eyeglass manufacturer exactly where to position the prism on eyeglasses that correct double vision.
- CYL stands for cylinder, or the amount of astigmatism in your eye. The cylinder and axis together help correct astigmatism.
- DV is an abbreviation for distance vision. This number indicates whether you have nearsightedness or farsightedness.
- NV stands for near vision, or the amount of power that needs to be added to make reading easier.
- OD means oculus dexter, or your right eye.
- OU stands for oculus uterque, or both eyes.
- OS is oculus sinister, or your left eye.
- PD means pupillary distance. Monocular PD is the distance from your pupil to the middle of your nose. Binocular PD is the distance from one of your pupils to the other pupil.
- Prism is used if you have double vision. It indicates the amount of prismatic power your glasses need to correct for differences in the alignment of your eyes.
- SPH means sphere, or the power of the lens that will correct your eyesight.
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Many of the abbreviations on your prescription will be followed by numbers.
If the numbers are marked with a plus sign (+) or no sign, you’re farsighted. If the numbers are marked with a minus sign (-), you’re nearsighted.
Some of the numbers in your prescription tell the eyeglass manufacturer how much correction your vision needs. Eyeglass strength is measured in diopters.
If your prescription reads -1.00, that means your eyeglasses need 1 diopter of strength to correct nearsightedness.
If your prescription reads +2.50, your eyeglasses need 2.5 diopters of strength to correct farsightedness. The higher the number, the more correction your vision needs.
Nearsightedness, or myopia, is a common refractive disorder. If you’re nearsighted, you can see objects that are close clearly, but objects that are farther away will look blurry.
With nearsightedness, your eye is usually elongated, with too much distance between the cornea at the front of your eye and the retina at the back of your eye. Nearsightedness can also happen if the cornea of your eye is too curved.
Due to this increased distance, light rays fall in front of your retina (a light-sensitive structure that sends signals to your brain) instead of on it. This can cause your distance vision to be fuzzy.
The lenses in your eyeglasses will
For a nearsighted prescription, the strength of the lenses will be marked with a minus sign. The more nearsighted you are, the higher the numbers will be.
For instance, a lens prescription of -5.00 is a stronger prescription than -2.00. The strength of the lenses can vary for each eye.
Farsightedness, or hyperopia, is a refractive disorder that makes close objects harder to see than distant objects. It happens because the distance from the cornea to the retina is too short or because the cornea of your eye is not curved enough.
If you’re farsighted, light focuses behind your retina instead of squarely on it.
For a farsighted prescription, the strength of the lenses will be marked with a plus sign. The more farsighted you are, the higher the numbers will be. For instance, a lens prescription of +4.50 is a stronger prescription than one that’s +2.00.
Correcting your vision with glasses or contact lenses, for both nearsightedness and farsightedness, may also help prevent:
- headaches
- eye strain
- burning or stinging in your eyes
Astigmatism is an irregular curve in either the lens or the cornea of your eye. This irregular curve can bend the light that enters your eye and affect the way it hits your retina. Astigmatism can blur both near and far objects. It can also distort the images you see.
Astigmatism is not unusual. In fact, The American Academy of Ophthalmology reports that 1 in 3 people have the condition.
If your astigmatism measures 1.5 diopters or more, you may need to wear prescription glasses or contact lenses to see properly. That said, if you have any amount of astigmatism, you may appreciate the extra clarity of wearing prescription eyewear.
Your prescription will indicate how severe your astigmatism is and where the irregular curve appears on your eye.
Your eyeglass prescription might also include notes from your optometrist or ophthalmologist about other features of your glasses or contacts. Your lenses might:
- be progressive or bifocal, meaning they correct for both distance and close-up vision.
- have an anti-reflective or anti-glare coating to reduce glare to make it easier to see at night or when working on a computer
- be photochromic, which means they darken or lighten depending on the lighting conditions around you
- be treated with a coating to make them more scratch-resistant
Yes. Because contact lenses sit directly on the surface of your eye, they need to have the same curves as your eye.
A contact lens prescription contains measurements for:
- Base curve: a number usually between 8 and 10 that conforms to the shape of your eye
- Diameter: the distance from one side of the lens to the other, usually around 13 to 15 millimeters
Your contact prescription also identifies the brand and type of lens, along with an expiration date. Contact prescriptions have to be updated from year to year to account for changes to your vision and to ensure they fit properly.
The American Optometric Association recommends that you have an eye exam at least every 2 years if you’re under 60 and every year if you’re over 60.
It’s important to have your vision and eye health checked regularly because some serious eye conditions, such as glaucoma, don’t have noticeable early symptoms.
An eye doctor can test your eyes and detect changes early, which may prevent vision loss. The tests are quick and painless, and can also help detect the following eye conditions:
- cataracts
- glaucoma
- age-related macular degeneration
Eye exams can also indicate when another health condition, such as diabetes or high blood pressure, may be affecting the health of your eyes.
The abbreviations and numbers on your eyeglass prescription tell the eyeglass manufacturer what type of lenses you need and how strong they need to be. This information also indicates the degree of nearsightedness, farsightedness, or astigmatism in each of your eyes.
Because contact lenses sit directly on the surface of your eye, they need additional information, such as the base and curve of your eye.
Your eyeglass or contact lens prescription isn’t a one-and-done situation. Over time, your vision can change, so it’s important to see an eye doctor at least every couple of years to protect your eye health.
