Decoding Your Eyeglass Prescription

Imagine this: you just had your annual eye examination and received a copy of your eyeglass prescription. You glance down at the page, and it looks like this:

Photo credit: OptomEyesLife

Example of an eyeglass prescription

With so many abbreviations and numbers (and not to mention the plus and/or minus signs), it can be confusing. While it may look like a secret code, your prescription is really quite simple to decipher. That’s why I put together the following guide to help you decode your eyeglass prescription.

1. OD, OS, OU

This represents which eye the prescription is written for. "OD" is the abbreviation for "oculus dexter," the Latin term for "right eye." "OS" stands for "oculus sinister," or "left eye." Rarely, you'll see "OU" which means "oculus uterque" or "each eye," indicating both eyes are the same. Nowadays, these abbreviations are commonly being replaced by "RT" and "LT" because they're easier to decipher (right eye and left eye, respectively).

2. Refractive Power (PWR or SPH)

This is the amount of power (measured in diopters) that you need to correct your vision. The further the number is from zero (known as "plano"), the more correction you need. A minus sign ("-") is for a nearsighted (myopic) correction, whereas a plus sign ("+") is for a farsighted (hyperopic) correction.

3. Toric Power (Cyl, Axis)

This represents the cylinder power (measured in diopters with a minus sign) and axis orientation (measured in angle degrees) needed to correct for astigmatism. If the cylinder column is blank (or says "SPH") then you don't have any astigmatism or it is too slight to need correction. Axis numbers usually range from 1 to 180.

4. Add Power (Add)

This represents the increase in magnifying power (measured in diopters with a plus sign) needed to correct for presbyopia. It is the extra power added to your distance prescription in order to see clearly up close. Add powers usually range from +0.75 to +3.00 D and will be the same power for both eyes.

5. Prism

This is the amount of prismatic power (measured in prism diopters) needed to compensate for eye alignment problems. It can be written as "p.d." or a superscript triangle when written freehand. Four abbreviations are used for prism direction (horizontal or vertical): BU = base up; BD = base down; BI = base in (toward the wearer's nose); BO = base out (toward the wearer's ear).

7. Pupillary Distance (PD)

This is the distance between the centers of each pupil (the black hole in the center of your iris). This measurement is needed to align the center of the lens with the center of the pupil, which is important for properly fitting lenses and visual comfort. This number can be written binocularly (both eyes) or monocularly (one eye), and varies when viewing at distance and near.

7. Issue & Expiration Date

By law, eyeglass prescriptions are valid for 24 months after the date of when the prescription was written. When your prescription expires, you won't be able to buy eyeglasses until your eye doctor writes an updated prescription. This will involve an eye exam to check your general eye health and refraction to determine your new prescription.

Additional Rx Information

In addition to the aforementioned abbreviations and numbers, eyeglass prescriptions should include the name of the patient, name of the prescriber, and the office's contact information.

Your eye doctor may include specific lens recommendations on your eyeglass prescription — such as anti-reflective coating, blue light protection, or photochromic lenses — to give you the most comfortable vision correction possible.

It is important to note that contact lens and eyeglass prescriptions are not the same. You need a separate contact lens prescription in order to purchase contact lenses.

Related Post: Decoding Your Contact Lens Prescription

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