Johnstone M. Kim, MD, is board-certified in ophthalmology. He's a practicing physician at Midwest Retina in Dublin, Ohio and previously served as a full-time faculty member at the Wayne State University School of Medicine and the Kresge Eye Institute in Detroit, Michigan.
If you need eyeglasses, you might be confused by the numbers, terms, and symbols on your prescription. However, there are important reasons why it's written the way it is.
Eyeglasses prescriptions use the same standard format and common notations. This makes them universal, meaning that they can be read anywhere in the world.
The article will use a sample eyeglasses prescription to walk you through how to read your own.
Providers who write eyeglasses prescriptions may Latin abbreviations. While they have been used for a long time, Latin abbreviations are becoming less common.
On your prescription, you might see abbreviations for specific terms instead.
For example, the word "power" is sometimes written as "PWR." Another common term is "sphere" which is sometimes abbreviated as "SPH" on a prescription.
OD: -2.00 – 0.50 x 180
OS: +1.00 DS
ADD: +1.75 OU
Here's what the Latin abbreviations on the example prescription mean:
In addition to terms and abbreviations, eyeglasses prescriptions also include a lot of numbers.
You'll also see some mathematical symbols like the plus sign (+) and minus sign (-).
In the example prescription, the first number to the right of OD is -2.00. This is the "sphere" part of the prescription, which may be abbreviated as "SPH."
The sphere number indicates whether you have nearsightedness or farsightedness.
Nearsighted people have trouble seeing things that are far away. Farsighted people have trouble seeing things that are up close.
You'll also see a plus sign or minus sign before the number.
The next number in the sample prescription is -0.50. This is the "cylinder" measurement. On your prescription, "cylinder" might be abbreviated as "CYL."
The cylinder measures the degree of astigmatism in your eye. The number shows how much lens power will be needed to correct astigmatism.
The next number is x 180, which is read as "axis 180." On your prescription, "axis" is sometimes abbreviated as "X" or "AX."
This number is an angle in degrees from 0 to 180. If you have astigmatism, this number points to where it is in your eye.
The cornea is the clear covering of your eye. It is the part of your eye that does most of the focusing.
It is common to write SPHERE or DS as a placeholder where the astigmatism number goes.
This helps make sure that the reader knows the provider did not forget to record the cylinder or astigmatism correction.
In the example, the left eye's "sphere" number is plus one (+1.00) DS.
The letters DS mean "diopters sphere." This number means the left eye’s correction is spherical with no astigmatism.
In other words, the right cornea probably has a slightly oblong shape while the left cornea is very close to being perfectly round.
In the example, the ADD number of +1.75 notes how much power needs to be "added" to the distance prescription. This addition helps a person see better for reading and other activities that they do up close.
Younger people's prescriptions usually do not have an ADD number. While some young people can have near-focusing problems, it usually develops as you approach 40.
Some people think the ADD number is the power needed for over-the-counter (OTC) reading glasses (or "readers"), but it's not the same thing.
To get the right number, you need to do a little math.
To find the right reading glasses, add the sphere number to the ADD number.
In the above example, for the right eye, this would be -2.00 and +1.75, which equals -0.25. For the left eye, add +1.00 and +1.75 to get +2.75.
Next, look at the cylinder measurement and the axis measurement.
In the example, the correct number for the right eye is -0.25 -0.50 x 180 while the correct number for the left eye is simply +2.75.
The example was chosen to show the difference between nearsighted and farsighted prescriptions. For most people, the numbers are usually similar in power for both eyes.
You may also see a few other words or abbreviations on your eyeglasses prescription:
Your eyeglasses prescription may include Latin abbreviations, numbers, and mathematical signs. These numbers are used to describe the shape of your eye and the correction you need in your glasses.
For example:
If you're confused about what the words and numbers on your prescription mean, ask your eye healthcare provider to explain them to you.
Vimont C, Turburt C. What do astigmatism measurements mean? American Academy of Ophthalmology. Published April 5, 2021.
MedlinePlus. Presbyopia.
Porter D. What is prism correction in eyeglasses? American Academy of Ophthalmology.
Polasky M. Monocular Subjective Refraction. In: Clinical Procedures in Optometry. Lippincott; 1991:174-188.
Troy L. Bedinghaus, OD, board-certified optometric physician, owns Lakewood Family Eye Care in Florida. He is an active member of the American Optometric Association.
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