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od vs os eye prescription

od vs os eye prescription

od vs os eye prescription

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od vs os eye prescription

Step one of understanding the prescription from your eye doctor is knowing OD and OS. These are simply abbreviations for Latin terms:

  • OD is an abbreviation for “oculus dexter” which is Latin for “right eye.”
  • OS is an abbreviation for “oculus sinister” which is Latin for “left eye.”

Your prescription might also have a column for OU, which is an abbreviation for “oculus uterque,” Latin for “both eyes.”

Although OS and OD are traditional abbreviations used in prescriptions for eyeglasses, contact lenses, and eye medicines, there are some doctors who have modernized their prescription forms by replacing OD with RE (right eye) and OS with LE (left eye).

OD is short for the Latin term oculus dexter which means right eye. OS is an abbreviation of the Latin oculus sinister which means left eye. You’ll often see this terms on eyeglass prescriptions.

od vs os eye prescription
od vs os eye prescription

What does OD mean?

The abbreviation OD is frequently used in eye care and has two distinct meanings. When OD is part of your lens prescription, it is the abbreviation for the Latin term Ocular Dexter, which means “right eye.” When OD is written next to your eye doctor’s name, it is the professional abbreviation for Doctor of Optometry.

There are many abbreviations used in eye care, and sometimes it can be difficult to interpret what they all mean. Another abbreviation you may see on your prescription is OS. This is the abbreviation for Ocular Sinister and is Latin for “left eye.” In computer terminology, OS can also refer to an operating system, but this is not what it refers to in eye care.

Understanding eye abbreviations when you visit your eye doctor will help you to make informed decisions about your eye care.

Sphere, Cylinder and Axis

The sphere (SPH) on your prescription indicates the lens power you need to see clearly. A minus (-) symbol next to this number means you’re nearsighted, and a plus (+) symbol means the prescription is meant to correct farsightedness. The cylinder (CYL) number indicates the lens power needed to correct astigmatism.

If this column is blank, it means you don’t have an astigmatism. An axis number will also be included if you have an astigmatism. This number shows the angle of the lens that shouldn’t feature a cylinder power to correct your astigmatism. A multifocal prescription will include an ADD value, sometimes marked as NV. This indicates the required strength for the near prescription in your lens. PD stands for pupillary distance, which is the distance between the centres of the pupils of your eyes. So now you know the basic terminology. Let’s see how those parameters look on the prescription.

od vs os eye prescription
od vs os eye prescription


The prism numbers represent the amount of prismatic power needed for your eyes. Prismatic powers are prescribed to help with eye alignment problems (vertical and horizontal). The need for correcting eye alignment is uncommon, so only a small number of eyeglass prescriptions include prism.

Nearsightedness and Farsightedness

Near the OS and OD headings, you’ll usually see numbers and plus (+) or minus (-) signs. They may be in a column labeled “sphere” or “S.” These describe your prescription’s strength.

The number represents diopters (which may be abbreviated as “D”), a unit of measurement that correlates to the amount of correction that is necessary. 1.00 stands for one diopter. However, the correction can be measured in one-quarter diopters. For example, 1.25 is one and one-quarter diopters.

Typically, the further away from zero, the stronger the prescription. For example, 3.50 means that more correction is needed in comparison to a 2.25.

The plus and minus let you know if you are near or farsighted. When a plus sign is in front of the number, that means you are farsighted. In farsighted individuals, objects closer to your eyes are typically blurry, but further away objects are clear.

When there is a minus sign in front of the number, that means you are nearsighted. Typically, objects close to your eyes seem clear, and those that are far away appear blurry.

If your prescription reads -2.00, that means you are two diopters nearsighted. If your prescription said +3.50, you are three and a half diopters farsighted.

ADD Number

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 40.2

ADD vs. Powers for Readers

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.
od vs os eye prescription
od vs os eye prescription


The pupillary distance, or PD, is the distance between the centers of each pupil (black hole). Once you reach adulthood, this number does not change. Moreover,The PD number is very important for properly fitting lenses and is required for optimum visual comfort and performance. The measurement of the proper PD enables the center of the lens to align with the center of the pupil.

I have astigmatism, what does that mean?

Individuals with astigmatism usually experience some degree of blur or distortion at all distances. In astigmatism, light comes into the retina at multiple focus points because of an irregular shaped cornea, which causes blurring. With astigmatism, one or both eyes can be farsighted, one or both eyes can be nearsighted, or one eye can be nearsighted while the other is farsighted.


Most of the time you will find that your eyeglass prescription is written in a grid-like format. It will contain terms, abbreviations, and numbers.

Along the left-hand side, you might see these abbreviations. Here is what those abbreviations mean:

O.D.- This is oculus dexter, meaning right eye.

O.S.- This is oculus sinister, meaning left eye.

O.U.- This is oculus uterque, meaning both eyes.

Along the top, you might see different verbiage that generally has to do with measurements related to different aspects of your vision.

SPH- This is short for sphere, and basically tells you how powerful your prescription needs to be in order to correct your vision

If you happen to see the letters ADD, this is how much more power you need if you are getting bifocals or progressive lenses.

CYL- This is short for cylinder. If you see this, this indicates astigmatism. This is a condition where the cornea is irregularly shaped and causes blurred or distorted vision. It also tells the lens strength needed to fix it.

AXIS- This describes the direction and degree of your astigmatism.

ADD- This is the added magnifying power you need in the lower part of a multi-focal lens. It’s used to correct presbyopia (the inability to see up close).

od vs os eye prescription
od vs os eye prescription

What do the numbers on my contact lens prescription mean?

Most of the abbreviations on a contact lens prescription are followed by numbers. Here’s what those numbers mean:

  • Positive (+) number – If a number has a plus sign before it, that means you’re farsighted.
  • Negative (-) number – If a number has a minus sign before it, that means you’re nearsighted.

For example, take a prescription with a PWR value of -2.25. This means you need 2.25 diopters of strength to correct nearsightedness. If that value were +2.25, that means you would need 2.25 diopters of strength to correct farsightedness.

How often does an eye prescription change?

Now that you’ve learned how to read the common measurements on an eye prescription, it’s important to know how often you may need an eye exam. Eye prescriptions may change, so it’s vital to have regular exams. If you’re an adult between the ages of 19 and 40, and you have vision problems, you need to check your vision at least every second year. If you’re older than 40, you should get checked once a year.

In case you have no vision problems, you can get checked every five years until you reach the age of 30. After turning 30, the exams should come every 2-4 years. After the age of 65, everyone needs regular eye exams at least once every two years.  Reading an eye prescription shouldn’t be hard if you know all the facts. Once you’ve learned how to decode your new prescription, all you need to do is find the perfect eyewear.

At Felix Gray, we carry a wide selection of Blue Light blocking prescription glasses and sunglasses. Shop now for top-notch fits and find your ideal pair.


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