How to Read Your Eye Prescription
If you’re wondering how to read your prescription, we’re here to help. You may be entirely new to wearing prescription glasses, or you’ve just received an up-to-date prescription from your eye doctor and want to understand what it means.
Read on to discover the ins and outs of your vision.
Understanding your glasses prescription
Your eyeglass prescription can be either digital or on paper, and it will look something like the example below. As you can see, these many abbreviations and optical terms can be intimidating.
If you’re wondering what OD and OS mean and all the other words on the chart, see the list of abbreviations below.
Eye prescription chart abbreviations
You might need a different prescription for each eye, so the prescription chart has a section for both. Note that some prescription charts might only have two different sections with no titles.
LE, L or OS: This indicates your left eye.
RE, R or OD: This indicates your right eye.
PD (pupillary distance): Knowing your pupillary distance (PD) is essential when ordering prescription glasses online. The PD is the distance between the centre of your pupils, measured in millimetres.
When you buy glasses online, you should enter your PD to ensure your prescription sits precisely where your eyes need it. The pupillary distance on your prescription is often located at the bottom of the prescription card.
If there is no PD on your prescription, you can use our pupillary distance tool to get it in minutes.
SPH (sphere): The value under SPH determines the lens power needed to correct nearsightedness or farsightedness, which is spherical because it’s the same across the eye’s surface.
Being farsighted is also known as hyperopia, which occurs when you struggle to see things up close while you see far away objects more clearly (even if still not crystal clear). If you are farsighted, the strength of the lenses will be marked with a plus sign in the sphere section.
On the other hand, nearsightedness, also known as myopia, is when you struggle to see far away. If you are nearsighted, your sphere eye prescription will be marked with a minus sign.
The more difficulty you have seeing objects up close, the higher your measurement will be. On the contrary, the more you struggle to see far-away things, the lower the measure on your SPH section will be.
CYL (cylinder): CYL in your eye prescription indicates the amount of lens power you need for astigmatism correction. Astigmatism is when an irregular curve in your eye’s lens or cornea can blur near and far objects. If your CYL section is blank, you have no astigmatism.
Axis: If your glasses prescription includes cylinder power, it must also have an axis on your eye prescription. The axis indicates the angle between an astigmatic eye’s two sections, ranging from 1 to 180.
If you have an axis on your prescription card, you need lenses to correct astigmatism.
Other eye prescription abbreviations
Prism: This section indicates the need to add a prismatic power to the lenses to bend light differently than regular ones. Prism glasses are prescribed to correct double vision, which happens when the eyes don’t work together.
Most prescriptions do not contain prism details. When they do, the optician will include the direction for the position of the prism “base.”
Abbreviations are used for prism direction: BU = base up; BD = base down; BI = base in (toward the wearer’s nose); BO = base out (toward the wearer’s ear). It is possible to have horizontal (BI or BO) and vertical (BU or BD) prism.
ADD (addition): Usually located on the far right side of your eye prescription, ADD stands for addition. It indicates the additional lens power needed for reading, which is used in multifocal lenses, reading glasses or progressive lenses.
Notes: The type of Rx glasses you need for vision correction may be noted on a glasses prescription, such as DV (Distance Vision/nearsightedness) and NV (Near Vision/reading).
Nearsighted prescription
Nearsighted prescriptions have values with a minus sign in the SPH (sphere) box for the right or left eye or both. This indicates that the eyeglass lenses will correct your myopia (distance vision)
Farsighted prescription
Farsighted prescriptions feature a number with a plus sign in the SPH box for the right or left eye or both, indicating that your eyeglass lenses should correct hyperopia (near vision).
Astigmatism prescription
If you suffer from astigmatism, your eye prescription will have a value in the CYL column indicating the lens power needed to correct astigmatism. There will also be a value in the Axis.
How bad is my eye prescription?
If you think your eye prescription is bad, it might be that you just saw too many numbers and terms on your eye prescription chart, and you’re now worried about it. You need to know that there is no bad or good eye prescription.
It may just be that your prescription is stronger than usual. For example, a refractive correction for nearsightedness of -5 diopters or more is often considered “high myopia,” whereas a prescription of +5.25 or more might be classified as “high hyperopia.”
How often does eye prescription change?
Your eyeglass prescription will probably change over time. This depends on your vision’s conditions and needs. Some people’s glasses prescription changes every two years. For others, it might take longer, like three or five years or even more.
The eyes grow older just like every other part of our body, so it’s only normal that, in time, our vision may need a little help. For instance, you can expect to develop presbyopia as you get older (it typically happens to most people in their thirties or forties).
To help correct this, you can get a pair of reading glasses or incorporate new progressive lenses into your regular frames.
DID YOU KNOW?
Both eyeglass and contact lens prescriptions will change over time depending on your vision condition. As we grow older, we will likely develop presbyopia and need a pair of reading glasses or progressive lenses.
How long is your eyeglass prescription good for?
You might also be wondering how long an eyeglass prescription is good for. Eye prescriptions often expire in two years. Your optometrist should include the date of issue and the expiration date on your prescription.
We recommend always checking your country’s laws regarding eye prescriptions and contacting your optician for regular check-ups.
What about contact lens prescription?
Glasses prescriptions and contact lens prescriptions are different. This is because glasses lenses correct vision at about 12 millimetres away from the eyes, while contact lenses sit directly on the eye’s surface.
Contact lens prescriptions also include values for base curve and diameter. During your eye exam, your eye doctor will fill in these values and determine the best type of contact lenses for your vision needs and eye health. Read more about how to read your contact lens prescription.
How to read an eye prescription
It should now be easier for you to understand all the abbreviations and numbers on your eyeglass prescription. Those are essential pieces of information for the lens manufacturers, as they indicate exactly what your vision needs.
For contact lenses, the eye prescription chart looks a bit different, but the concept is the same. Your prescription will likely change over time, so make sure you plan regular vision checkups every couple of years!
