What Does Your Vision Prescription Really Mean?

Mar 24 2020
Unless you’re an optometrist or optician yourself, looking at a vision prescription, with all of its cryptic symbols and abbreviations, can be like trying to read an encoded message — you’re left guessing at what it all means. We believe that you should understand a vision prescription just as well as you understand a prescription for medication, sent to the pharmacy by your doctor. We’ve taken some time here to decode and explain the different parts of your vision prescription so that you can understand just what it’s saying about your eyes.

It’s Like Reading Latin… Because It Is Latin!

When you look at your prescription, you’ll see two categories: OD and OS. These are Latin abbreviations meaning oculus dextrus (OD) and oculus sinister (OS). This may appear confusing at first, but these two terms refer to the right eye and the left eye, respectively. Sometimes, a vision prescription will have an “OU” abbreviation which stands for oculus uterque, meaning both eyes. If remembering what OD, OS, and OU stand for just gets too confusing, it can be simpler to remember that the right eye is always listed on your prescription before the left eye. Importance of Understanding Your Prescription

Are You Nearsighted or Farsighted?

You’ll often see a plus (+) or minus (-) sign next to the numbers listed on your prescription. These signs will indicate if you’re nearsighted or farsighted. A minus sign indicates that you have degrees of myopia, which is commonly referred to as nearsightedness. Nearsightedness means that you can see nearby objects clearly, but far away objects appear blurry. A plus sign indicates that you have degrees of hyperopia, or farsightedness. Those who are farsighted can see objects that are far away clearly, but objects that are nearby are blurry.

So, What Are Those Other Abbreviations on Vision Prescriptions?

Now that you understand what OD, OS, and OU stand for, we’ll explain the other categories listed on your prescription and describe what each says about your vision. Abbreviations on Vision Prescriptions

Sphere (SPH)

The number listed under the sphere (SPH) category indicates how strong your vision prescription is. Sphere means that your correction is spherical and is equal in all portions of the eye. In general, the further away a number is from 0, the stronger your prescription and the more vision correction you require. These numbers are measured in diopters (D), a measurement that usually isn’t included on your prescription.
Measurements of nearsightedness: Measurements of farsightedness:
  • -3.00 diopters or less is mild
  • -3.00 to -6.00 diopters is moderate
  • -6.00 to -9.00 diopters is severe
  • -9.00 diopters or more is extreme
  • +2.00 diopters or less is mild
  • +6.00 diopters or more is extreme

Cylinder (CYL)

CYL refers to cylinder, which measures how much astigmatism you have. Astigmatism is when the curvature of the eye’s cornea is misshapen and causes distorted vision. If you don’t have any number listed in the cylinder category, that means that you don’t have an astigmatism.
Measurements of astigmatism:
  • 1.0 diopters or less is mild
  • 3.0 diopters or more is extreme
These numbers under the cylinder column can be either positive or negative depending on whether your astigmatism causes areas of nearsightedness or farsightedness.


The axis category is also related to astigmatism. The misshapenness of the cornea can occur in different areas of the eye, so the axis reveals where the astigmatism is oriented. The degrees of an axis can range from 0 to 180 degrees.

Addition (Add)

A few vision prescriptions will include the term “add.” Add stands for addition and is used to correct presbyopia. Presbyopia is farsightedness that occurs when the lens of the eye loses elasticity as a result of aging. It requires you to use bifocal, reading, or varifocal glasses in order to see nearby objects clearly. The add value represents how much additional vision correcting power you will need added to your distance prescription.

Contact Lens and Glasses Prescriptions Aren’t the Same!

Because contacts rest on your eyes and glasses rest on your nose, the focusing power of your contact lenses and the lenses in your frames will be different. This means that just because you wear both contacts and glasses, it doesn’t mean that you can use the same prescription for both — make sure to get a designated prescription for each.

Why Understanding Your Prescription is Important

Your prescription can tell you a lot about your eyes — for example, understanding how severe your refractive error is can help you make an informed decision about your options for vision correction. Certain refractive surgeries are better for different vision conditions, and the strength of your prescription may affect the cost. Knowing your prescription also helps you understand your overall eye health. Taking greater accountability for your eye care and health is important because it can help you identify subtle changes in your vision. These can signal issues that can become potentially severe if not noticed and treated as early as possible.

It’s Time to Update Your Prescription

Now that you know how to read your vision prescription and understand your vision correction, when’s the last time you’ve had that prescription updated? Your eyes are constantly changing, and so is your prescription! While the OS, OD, SPH, and CYL categories won’t change, the numbers within can. To ensure that you can see life clearly, it’s important to schedule a routine eye exam at Central Oregon Eyecare. If you need to have your prescription updated, or want to learn more about what your prescription says about your eyes, schedule an appointment or call the location closest to you.

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