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OD vs OS: A Beginner’s Guide to Eye Prescription Terms and Abbreviations

OD vs OS: A Beginner’s Guide to Eye Prescription Terms and Abbreviations

In the 21st century, eyeglasses have become part and parcel of our everyday lives. According to a recent survey by the Vision Council of America, 4 billion adults in the world (75 per cent of the global population) wear glasses, and the number is constantly increasing. Thus, it is most likely that you or at least your loved ones have joined the ‘four-eyed’ squad. So, it is quite reasonable to try and understand eye prescriptions.

Moreover, as many of us are now turning to online retail stores to purchase spectacles, the process of understanding eyeglass prescriptions has become all the more important. In online stores, you have to fill in your prescription in their order form. So, if you cannot make sense of your eye prescription, you might end up buying incorrect lenses. Thus, the culmination is vision distortion and a futile buy.

In this blog, we are here to explain the A to Z of eye prescriptions, so that you are equipped with the right knowledge, and can ace the mechanism of buying glasses online!

OD vs OD in Eye Prescription

The first step in grasping an eye prescription is knowing the meaning of OD and OS. Well, they are abbreviations for Latin terminologies.

  • OD - It is the abbreviation for ‘oculus dexter,’ which is Latin for ‘right eye.’
  • OS - It is an abbreviation for ‘oculus sinister,’ which is Latin for ‘left eye.’

It is noteworthy to remember that OD and OS are traditional abbreviations utilised in eye prescriptions, contact lenses and eye medicines. But, some doctors have modernised prescriptions by replacing OD with RE (Right Eye) and OS with LE (Left Eye).

But, the explanation of an eye prescription does not end with OD and OS. There are other abbreviations that you must know. What are they? Let us find out!

Additional Eye Prescription Terms and Acronyms Everyone Must Know About

OD vs OS - Eye Prescription Explained
  • OU - It is the abbreviation for ‘oculus uterque,’ which is Latin for ‘both eyes.’

  • SPH - It is the abbreviation for ‘sphere’ on your prescription. SPH indicates the lens power you would need to see clearly. It is prescribed by the ophthalmologist to describe whether you are near-sighted or far-sighted. The term ‘SPH’ has a number by its side. A minus (-) sign implies you have nearsightedness (can see nearby objects clearly), and a (+) sign indicates that you are farsighted (can see distant objects clearly)

  • CYL - It is the abbreviation for ‘cylinder number,’ which indicates the lens power prescribed to correct astigmatism. In simple words, we can understand astigmatism as a refractive error, wherein the eye’s curvature is imperfect. The condition causes both near and distant vision to get blurry. In an eye prescription, if the CYL (cylinder) column is left blank, it means that you do not have astigmatism. On the contrary, the larger the number on the column, the greater the astigmatism.

  • Axis - An Axis number also becomes part of an eye prescription if you have astigmatism. It can be anywhere from 1 to 180. The number reveals the angle of the lens that should not feature a cylinder power to correct your astigmatism. In other words, the Axis number indicates where the astigmatism is located on the cornea.

  • Add - It is a terminology used in multifocal lenses or varifocals to demonstrate the additional magnifying power for the bottom section of the lens. This column is mostly active for individuals with presbyopia.

  • Prism - At times, an eye prescription may contain a column for ‘prism’ or ‘base.’ It is active if a correction is necessary for eye misalignment. The base value for a prism correction can be either ‘i,’ or ‘out.’ Besides, you might see abbreviations like BI, BO, BU, or BD, on the prism column.

  • PD - It is the abbreviation for ‘pupillary distance.’ PD measures the distance between your eyes’ pupils.

So, there we have it, a crisp overview of how to read eye prescriptions. Now that we have covered most of the important terms and abbreviations, let us further delve into the topic.

Common Lens-related Abbreviations You Must Know About

Nowadays, spectacle lenses are of varying types, and they are infused with unique features. Some of the terminology used to describe these features are -

  • SV - Single vision lenses, which is only one prescription throughout the lens.

  • BF - Bifocal lenses, which correct both near and distance vision. They have a demarcating line, wherein the bottom section is for near prescription and the top section of the lens is used for a distance prescription.

  • PAL - Progressive addition lenses. They seamlessly progress from distance to intermediate to near vision prescription, without any demarcating line.

The best frames for varifocals lenses have a large surface area, and our BUSK 4 makes the cut!

  • AR - It is the abbreviation for ‘anti-reflective.’ The coating is used on lenses to reduce glare.

  • SH - It is the acronym for segment height, which measures the distance from the top of the near vision section of the lens to the bottom of the lens in millimetres.

What Do the Numbers on an Eye Prescription Mean?

Let us finally wrap up the blog by examining the numbers on an eye prescription. You will notice that every vision prescription has a positive or negative number next to its many columns. These numbers indicate the power required for the specific section of the lens. They inform your optician on how the lenses of the eyeglasses are to be cut.

  • Negative Numbers - An eye prescription will have negative numbers (-) under the SPH column if you are nearsighted.

  • Positive Numbers - An eye prescription will have positive numbers (+) under the SPH column if you have farsightedness or hyperopia.

  • Range - Usually, the numbers in the SPH column range between 0.00 to +/- 20.00. On the contrary, the numbers in the CYL column range between +/- 0.25 to +/- 4.00.

Taking Extra Care of Your Eyes is Worth It

So, there it was, a crisp overview of eye prescription explained. Eyes are among our most precious sensory organs, and they deserve extra care, love, and attention. Knowing the basics of an eye prescription is one way to be more mindful of your vision needs. Likewise, it is equally important to get regular eye tests and have your lens prescriptions updated in a timely fashion. At Specscart, we offer a free glasses Home Trial of four frames and 3 lenses, so that you can try different eyeglasses from your home’s comfort.


  • https://www.aao.org/eye-health/diseases/what-is-astigmatism
  • https://thcsnguyenthanhson.edu.vn/20-how-many-people-wear-glasses-full-guide/
  • https://www.healthline.com/health/od-vs-os#other-abbreviations
  • https://www.cbs.nl/en-gb/news/2013/38/more-than-6-in-10-people-wear-glasses-or-contact-lenses
  • https://www.mayoclinic.org/diseases-conditions/astigmatism/symptoms-causes/syc-20353835

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