There are several details that an eye prescription covers. These details are used to ensure your prescription glasses give you the best possible vision correction. But because there are so many details, and they’re often abbreviated, decoding your eyeglasses prescription can feel like learning a new language.
Rest assured, what may seem like a complex code of abbreviations is easy to crack. This article will go behind the numbers to help you understand your glasses Rx. Doing so helps you be knowledgeable about your eye health, track any changes in your vision, and talk comfortably with your eye care provider.
While the format of a glasses prescription can vary, it’s usually laid out like a grid with two separate rows: one row for the left eye and one row for the right eye. There are also a series of columns that designate the specifics of a prescription.
To give you a crash course in those details, here’s a quick overview:
Keep reading for more information on these details, including their abbreviations and what they mean for your vision.
Now that the basics have been covered, we can move on to covering what each of these specifications means for your vision. When looking at your prescription, if there are boxes that are left blank, it’s because that specific detail doesn’t apply to your eyesight. If there’s a number in a particular box, it’s because correction is needed in that area.
The numbers in each box vary because they reflect different things. For example, in the Sphere and Cylinder boxes, the numbers specify how severe the refractive error is. But in the Axis box, the number specifies a certain area of the eye that needs correction.
Vision is measured in diopters, a unit used to determine what is needed to correct common problems. Read on for more about the specific optical terms and what they mean when it comes to your eyewear Rx.
Every prescription is separated into two rows: OD and OS. OD stands for oculus dexter, which means the right eye. OS stands for oculus sinister, which means the left eye.
These abbreviations are used because it’s common for each eye to have different prescriptions. Separating the details for each eye makes it easier for the eye doctor to notate a person’s vision needs, and makes it easier for the lens manufacturer to follow.
You may just see RE for “right eye” and LE for “left eye,” as some doctors have moved away from the traditional Latin prescription terms. Though it’s not always present on a vision Rx, you may also see the abbreviation OU. It stands for “oculus uterque,” which means the prescription for both eyes is the same.
SPH refers to the lens power you’ll need to achieve 20/20 (or at least optimal) vision. The number under the sphere column determines the strength of correction you’ll need. The further the number is from 0, the worse your eyesight is and the stronger your prescription will be.
In front of the number will either be a minus sign (-) or a plus sign (+). A minus sign indicates you have myopia, or nearsightedness. This means you need help seeing objects at a distance. A plus sign means you have hyperopia, or farsightedness. This means you need help seeing things close up.
An eyeglass lens that only contains a distance prescription or near-vision prescription (with or without a CYL) is known as a single-vision lens.
CYL is used to denote the lens power you’ll need to correct astigmatism. If the cylinder field is blank or says “SPH,” you don’t have astigmatism. It could also mean you only have a very mild case that doesn’t need correcting.
It’s possible to have astigmatism on its own, or in addition to other refractive errors. If it’s in addition to another vision problem, the number will have either a minus sign to indicate nearsighted astigmatism, or a plus sign to signify farsighted astigmatism.
If your Rx indicates that you need a cylindrical lens power (for astigmatism), an axis number will always follow. The axis number tells the eyeglass manufacturer the direction (axis) on your lens the astigmatism correction should be located.
The number is always somewhere between 1 and 180, which indicates the axis of the eye. If you imagine your eye as a circle and draw a horizontal line to halve that circle, the axis is one-half. If you think back to high school geometry, you’ll remember that “90” is the vertical line drawn straight up and down (the vertical axis). “180” is the horizontal line (the horizontal axis).
People who have the ADD portion of their eyeglass prescription filled out need correction at near and far distances. A lens that corrects at multiple distances (with or without a CYL) is known as a bifocal or multifocal lens.
The number in the ADD column represents the magnifying power that will be added to the lower half of bifocal or multifocal lenses to help restore your near vision. This number is typically the same for both eyes.
The last two terms on the prescription are Prism and Base. Some eyeglasses have a prism added because the person’s eyes are not properly aligned. Imagine car headlights that aren’t lined up and one is turned in, for example. However, this is not a common problem, so this field is usually left blank on your Rx.
The base indicates where the thickest edge of the prism will be: BU (base up), BD (down), BI (base inward, toward the nose), or BO (base outward, toward the ears). The base direction tells you where the prism will redirect light.
Plano is the term used to describe glasses that offer no vision correction. In other words, someone with 20/20 vision or better would have a plano prescription because they don’t require any corrective measures.
Let’s put the above information into practice. During an eye exam, your optometrist or ophthalmologist will determine your visual acuity and tailor your prescription accordingly to ensure your glasses provide the most clarity.
Here’s an example of something you might see on your prescription chart:
This means that the right eye (OD) has -2.00 (or 2 diopters) of nearsightedness. This is a relatively low amount of nearsightedness. The second column denotes -1.00 diopters of astigmatism, and this person will need a 100-degree axis to correct the issue. As you can see, the left eye (OS) is very similar, with slightly more nearsightedness and slightly less astigmatism.
These numbers will determine the thickness and curve of the lenses needed to correct the wearer’s vision and make it the best it can be. If the nearsightedness was more severe — say -7.00 diopters — the eyeglass lenses would need to be thicker.
The same can be said for positive numbers, which indicate farsightedness. If the prescription reads +2.00, then the wearer needs two diopters of power to see things up close.
No. An eyeglasses prescription cannot be used for contact lenses. Please read our Contact Lenses FAQs. A contact lens sits directly on the eye, so a special fitting is needed to make sure the contact lenses fit correctly on the eyes. The prescription is often different between glasses and contact lenses. Contact lens prescriptions include information from this fitting and a standard glasses prescription does not.
If you’re interested in wearing contacts, let your eye doctor know. They can make sure to measure you for glasses and contacts at the same appointment.
Your eyeglasses prescription can be applied to sunglasses, so you can have visual clarity both indoors and outdoors. Frames Direct has many sunglasses that are eligible for prescription lenses. So, once you have your updated Rx, you can start shopping for your new favorite pair.