How to Read Eye Prescriptions

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After having an eye exam, many people wonder how to read eye prescriptions. If you don’t know what OD and OS eye abbreviations mean, you’re not alone. The good news is reading eye prescriptions isn’t science fiction.  All those abbreviated terms make perfect sense, and all you need to do is learn which refers to what.

In this article, we will help you understand the meanings of the different letters and columns you may see on your eye prescription. Once you understand the way a prescription describes your vision, you will be able to read it with a deeper understanding.

Understanding the acronyms on your prescription

If you want to learn how to read prescriptions for glasses, you must start with decoding the acronyms and abbreviations commonly found in them. After an exam, your doctor will prescribe eyeglasses or contact lenses, or both. There are different ways in which ophthalmologists may write prescriptions. Most of them are handwritten or printed in horizontal rows.

The first thing you should learn is that the abbreviations OD and OS represent the Latin terms oculus dexter (right eye) and oculus sinister (left eye).  

An eye prescription chart may include several numbers and abbreviations, including:

  • O.D. (right eye) or O.S. (left eye)
  • O.U. (both eyes)
  • AXIS (the direction of astigmatism correction)
  • ADD (multifocal and bifocal lenses require this additional power management)
  • CYL (used to identify astigmatism and called cylinder correction)
  • DV (distance vision)
  • NV (near vision)
An example of an eyeglasses prescription

Reading different prescription formats

Whether the prescription is vertical or horizontal, the most important thing is knowing how to read the letters and numbers and understanding what each refers to. It’s not enough to only know the meaning of OD or OS.

The spherical correction measured in diopters is the first number you should expect to see after the common O.D., O.S., or O.U. It’s marked as SPH and used to identify how strongly the lenses need to correct your vision. A minus (-) next to the number means you are nearsighted. A plus (+) next to it or no sign at all means you’re farsighted. A high number means you need a strong prescription, regardless of the plus/minus signs.

Regardless of format, a vision prescription often includes the pupillary distance as a measurement, too. Marked as PD, it refers to the distance between your pupils.

How is a glasses prescription different than a contact lens prescription?

The measurements given for prescription eyeglasses and contact lenses are never the same. Learning how to read an eye prescription for both may be important to some people, but learning the difference between them is crucial for everyone.  An eyeglasses prescription is valid for glasses only. It doesn’t contain the vital information a contact lens prescription has. The only way to obtain this information is by going through a contact lens fitting and consultation.

A contact lens prescription specifies the lens diameter, the back surface contact lens curve, and often the manufacturer or lens brand that specializes in specific vision conditions.

Eyeglass prescriptions are usually stronger than contact lens prescriptions because we wear contact lenses directly on the eye’s cornea, while we wear the glass lens further away from the surface of our eyes.

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Pupillary distance and how to measure it

You can’t learn how to read eye prescriptions without learning more about pupillary distance. It’s a vital measurement that should be as precise as possible because it determines where you look through the lenses. The average PD of an adult is anywhere between 54-74 mm, and between 43-58 mm for kids. An ophthalmologist will usually measure your pupillary distance during a regular exam. However, in case your doctor hasn’t made this measurement, there is an easy way to do it by yourself.

Measuring Pupillary Distance

  • Stand 8 inches away from a mirror
  • Grab a ruler and hold it straight against your brow
  •  Align the 0 mm of the ruler with the center of your left pupil. Do this by closing your right eye
  • Look straight ahead, then close your left eye, but open the right one
  • The line of the ruler that’s lined up with the center of your right pupil is your PD

If you have any questions when measuring your pupillary distance, you can always reach out directly to our Customer Experience Team at [email protected].

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.