Updated on February 18, 2021. Reviewed by Chris Day (Optician)andDr. Justin Asgarpour (Optometrist).
Looking for an easy explanation on how to read your glasses or contact lens prescription? You’re in the right place.
We’ll help you understand what your eye care professional means by all those numbers and letters on your prescription, so you can enter these details with confidence when you shop for eyewear online.
There’s one key thing to remember about glasses and contact lens prescriptions: the measurements are different.
A glasses prescription is intended for the purchase of glasses only – it does not include information that is required in a contact lens prescription. If you wear contacts, you’ll need a prescription specifically for contacts. (More on that later)
Read on to learn everything you need to know about how to read glasses and contact lens prescriptions before shopping for eyewear.
Prescription eyeglasses and contact lens prescriptions: FAQ
Let’s start with some of our most frequently asked questions about glasses and contact lens prescriptions. Follow our guide to find the answers on how to read glasses prescriptions:
- What do the numbers on my prescription mean?
- How do I read my glasses prescription?
- What is the difference between progressive, bifocal and single vision glasses?
- How do I read contact lens prescription?
- What are the key differences between a glasses and contact lens prescription?
The following tips will help you decipher and understand your eyewear prescriptions. If you get stuck, get in touch with our Customer Service team. We’ll be happy to contact your Eye Care Provider to verify your prescription for you.
What do the numbers on my prescription mean?
Your prescription may include the following: SPH, CYL, Axis, ADD and Pupillary Distance (PD).
The first four parameters have to do with your visual correction. PD is a crucial measurement we need to make your glasses.
Here’s the meaning behind each of these letters and numbers on your glasses prescription:
1. OD “oculus dexter” indicates your right eye’s parameters.
2. OS “oculus sinister” shows your left eye’s parameters.
3. SPH “sphere” indicates the amount of lens power prescribed for nearsighted or farsighted vision. It is measured in diopter and uses (+) for farsightedness (hyperopia) and (-) for nearsightedness (myopia).
4. CYL & AXIS: a Cylinder (CYL) and Axis number (between 0 and 180 degrees) are required to correct Astigmatism. Both parameters will be required together.
5. ADD: provides magnifying power for reading, bifocal, multifocal and progressive lenses. You will most likely have the same number for both eyes that usually ranges between +0.75 and +3.00. Occasionally, lower add powers than +0.75 can be found on a prescription. These are for Anti-Fatigue lenses such as our SightRelax lenses.
There is a separate prescription for your right eye and your left eye. Most of the time, OD and OS are indicated on the left of your prescription and the following numbers show each eye’s specific needs. Some glasses prescriptions also include additional numbers such as:
6. Prism: measured in prismatic diopter (p.d.). It is required when eye alignment needs assistance. It is indicated as follows:
- BO (base out)
- BU (base up)
- BI (base in)
- BD (Base-down)
Each one of these indicators provide information about the base direction or the thickest edge of the prism. Clearly does not offer prism prescription glasses.
In addition to the general parameters, eyeglass prescriptions can require a Pupillary Distance (PD). Your PD is the distance between the centre of one pupil (the central black dot of your eye) to the centre of the other pupil. It is measured in millimetres and is an important part of your prescription.
PD indicates where the optical centre of your lenses should be placed, so you can have the best, most comfortable vision. It is generally mentioned in your eyeglasses’ prescription with the letters ‘PD’. If you can’t see it, you can learn how to measure your pupillary distance.
How do I read my glasses prescription?
Once you understand the sections of your glasses prescription, you’ll be able to figure out what all those numbers mean.
If you see a – , it indicates nearsightedness. If you see a +, it indicated farsightedness. If you notice an ‘Add’ power, it means you require magnifying lenses, such as progressives.
When you’re buying glasses online, all you need to do is make sure the numbers on your prescription match the numbers in the prescription field on your screen.
In the sample below, the right eye is prescribed -2.50 sphere to correct nearsighted vision. This eye needs a cylinder of -0.75 and an axis of 173 to correct astigmatism, and an ADD power of +2.25 to correct near vision. The ADD value is usually present in a multifocal prescription.
The left eye is prescribed with a sphere of -3.00 to correct nearsighted. This eye needs a cylinder of -1.00 and 004 to correct astigmatism, and an ADD power of +2.25 to correct near vision. Without the ADD value, it is a single vision prescription.
This is the correct way to include the numbers on our website for glasses:
What is the difference between progressive, bifocal and single vision glasses?
The differences between each type of glasses are not always clear. To understand how to correctly read a prescriptions for glasses, here is an overview of the main categories of lenses that can be written on your prescription.
1. Single vision lenses: a large majority of glasses come with single vision correction. This common type of lens is generally used to correct nearsightedness, farsightedness or used as reading glasses.
2. Bifocal lenses: these glasses come with two vision corrections. One is on the lower part of the lens to help you read or see from near, and the other on the upper part includes a distance prescription.
3. Progressive lenses: multifocal lenses offer multiple corrections in one pair. These prescriptions have a no-line lens and offer intermediate distance vision, which can be adapted for certain specific uses, such as computer work.
Special features on my prescription
You may also find additional information on your glasses prescription such as the suggestion of certain types of lens coating and special comments from your optometrist.
1. Lens designs on a prescription indicate your eyesight requirement, detailing the lens’ design and function (single, progressive, bifocals…). Occasionally, you’ll see a specific brand of progressive or single vision lens written on the prescription itself. This is most often a recommendation based on a brand the doctor’s office carries. If you have questions about anything on your prescription, feel free to give a call to our customer service team.
2. Vision enhancement: a special treatment for one or both lenses used to improve vision and clarity through your glasses. You could find different options such as:
a. Anti-reflective coating: enhances clarity and concentration by allowing more light to come in and reduces reflection.
b. UV protection: to prevent your eyes from being damaged by the sun’s UVs, your lenses can come with special anti-UV treatment.
c. Transitions: these lenses are equipped with a technology that adjusts your glasses’ tint according to the light. When the sun comes up, your glasses turn into sunglasses!
d. Polarized: improved glass technology designed to filter and reduce glare. Polarized lenses offer more clarity and a sharper vision to their wearers.
e. Clip-on glasses: additional lenses that can be adjusted on top of your prescription glasses. They can be polarized and come in various formats..
f. Blue light blocking glasses: a special coating that protects your eyes from artificial light by reflecting blue lights that come from digital devices. Clearly’s blue light glasses are also scratch-resistant and anti-glare to offer you clear and sharp vision.
Remember: glasses and contact lens prescriptions are different.
If you want to purchase contact lenses, you’ll need a specific prescription from your eye care professional. In addition to the general parameters that we’ve mentioned, a contact lens prescription will include a Base Curve and a Diameter.
The differences: Base curve (BC) and diameter (DIA)
If you’re not sure whether you have an eyeglass or contact lens prescription, verify whether your prescription includes:
1. Base Curve (BC): the number that indicates your contact lens’ shape. According to the steepness or flatness of your cornea, your prescription indicates how large your contact lens should be.
2. Diameter (DIA): a number indicating your contacts’ length to make sure they’ll cover your cornea properly.
3. Brand: your eye doctor will determine the appropriate brand and type of contact lenses for you, according to your preferences and specific requirements.
4. Expiration date: your eye care professional will determine an expiry date for your prescription. Past that date, you’ll require a new prescription for contact lenses. These are generally set annually.
5. Corrective power: these are the numbers associated with the actual power needed in your lenses. These numbers often change (or disappear) between your glasses prescription and your contact lens prescription, especially with higher powers.
If you find the information displayed above on your prescription, you have a contact lens prescription.
Both the Base Curve (BC) and Diameter (DIA) of a contact lens ensures a proper fit on your cornea and total eye surface. Those features ensure comfort and encourage eye health, including allowing proper oxygen to the eye. You’ll also need this information if you want to order contact lenses online.
Do you have a valid eye prescription and are ready to shop?
Now that you understand how your eye prescription works, you can learn how to buy glasses online at Clearly.
Pick a pair of frames online and enter your prescription details. You’ll soon be rocking a pair of glasses that look great and make everything around you look great as well. Click to browse our collection of stylish and affordable glasses.
Fancy getting contact lens delivered straight to your door? Click to check out our wide selection of contact lenses.
Have more questions? We have various other ways to help you read your eye prescription. Contact us by email, live chat or phone.
- Eye - Which eyes the prescription line item is for. ...
- SPH - Sphere (this can also be referred to as Power or PWR)
- BC - Base Curve (usually a number between 8 and 10)
- DIA - Diameter (usually a number between 13 and 15)
- Brand - The brand/type of contact lens that your doctor has fitted you for.
In general, the prescriptive power of a contact lens will be somewhat less nearsighted than eyeglasses. So in most simple words, the power of a contact lens will be lower than the eyeglass prescription. Reason being the distance of the lenses from the surface of the eyes.Can you use the same prescription for glasses and contacts? ›
The answer is no. While they both have the same objective — to correct what eye doctors call “refractive errors” that prevent you from seeing correctly — prescriptions for eyeglasses and contact lenses are distinctly different.How do I read my eye test results? ›
In general, the further away from zero the number on your prescription, the worse your eyesight and the more vision correction (stronger prescription) you need. A “plus” (+) sign in front of the number means you are farsighted, and a “minus” (-) sign means you are nearsighted.Why are my glasses better than my contacts? ›
Glasses reduce the need to touch your eyes, which means you're less likely to irritate your eyes or develop an eye infection. If you suffer from dry eyes, sensitive eyes, or allergies, glasses won't make the problem worse in the way that contact lenses could. Glasses tend to be cheaper than contacts.How do I know my contact lense power? ›
If a GP lens is selected with a base curve radius that's one-half diopter flatter (less curved) than the cornea, a contact lens power of -2.75D would be predicted. If the base curve radius is a half diopter steeper (more curved) than the cornea, a contact lens power of -3.75D would be predicted.Is it better to over correct or under correct vision? ›
No benefits of over-correction of myopia was found. The overall findings are equivocal with under-correction causing a faster rate of myopia progression. There is no strong evidence of benefits from un-correction, monovision or over-correction. Hence, current clinical advice advocates for the full-correction of myopia.Why are my glasses and contact prescriptions different? ›
However, contacts and glasses prescriptions are actually slightly different because of their distance from your eyes. Eyeglass lenses are placed approximately 12 millimeters away from your eyes, while contact lenses sit directly on your corneas.Are contact and glasses exams different? ›
Comprehensive eye exams are an in-depth vision and eye health exams that test your visual acuity and for certain eye diseases. Exams for contacts, by contrast, only check your visual acuity and fit you for contact lenses.What is the difference between glasses and contact lens prescription? ›
Is a contact lens prescription different from an eyeglass prescription? Because eyeglasses sit slightly away from the eye, and contact lenses sit directly on the eye, prescriptions for each are different. People who wish to use both eyeglasses and contact lenses will require two prescriptions.
A plus sign would mean they are farsighted. This second number, -0.75, indicates the person has an astigmatism, which is a distortion in the shape of the cornea that causes blurred vision.What is a good eye test score? ›
Visual acuity of 20/20 is considered “perfect vision” because no aids are required to see better, but people can have better than 20/20 vision. Many young people are able to see letters smaller than the general “20/20” size.What do the numbers mean on an eye exam? ›
The top number is your distance in feet from the chart. The bottom number is the distance at which a person with normal eyesight can read the same line. For example, if you have 20/30 vision, it means your vision is worse than average. Twenty feet away, you can read letters most people see from 30 feet.Why is my vision blurry with contacts but not glasses? ›
Some of the possible causes of blurry vision while wearing contacts include a change in your prescription, deposits (like dirt) on the lens surface, dry eyes, allergies, infections, or other eye health problems.What is the strongest contact lens prescription? ›
What is the strongest contact lens prescription? Contact lenses can be prescribed for extreme degrees of myopia, even for those who need correction of more than -20 Dioptres. Some lenses can go over -30 Dioptres. For monthly soft contact lenses, the highest level of corrective power is about -12 Dioptres.What is the maximum negative eye power? ›
For people with extreme nearsightedness, defined as a prescription of -6.0 diopters or more, it may be difficult to see anything more than a foot or so away from the face. In addition to making sight difficult, high myopia can come with severe complications.How can I measure my eye power at home? ›
- Print or purchase a vision chart. ...
- Tape the chart on a wall. ...
- Place your child's chair ten feet away from the chart.
- Ask your child to cover one of his or her eyes. ...
- Light the vision chart. ...
- Have your child read each line of the chart. ...
- Repeat the process with your child's other eye covered.
Prescription. Prescription This is easy to understand. For the same index, the higher the prescription, the thicker the lens is.Are blurry eyes normal with new contacts? ›
Some blurriness is common for new contact lens wearers. The distortion usually results from dryness. To counteract the moisture loss, talk to your eye care practitioner about medicated eye drops or pick up over-the-counter drops from your favourite drugstore.
After a treatment for farsightedness, an overcorrection would make you temporarily nearsighted. In this case, your distance vision would be somewhat blurred and your near vision rather good. Following a treatment for nearsightedness, an overcorrection would make it more difficult for you to see objects up close.
Until you adjust to your new prescription glasses, it might appear that your new glasses don't correct your vision as well as your old pair. This is completely normal. Most people find that it can take anywhere from 5 minutes to a few days to adjust to their new prescription glasses.What is the difference between glasses and contact lens prescription? ›
Is a contact lens prescription different from an eyeglass prescription? Because eyeglasses sit slightly away from the eye, and contact lenses sit directly on the eye, prescriptions for each are different. People who wish to use both eyeglasses and contact lenses will require two prescriptions.What does 1.75 mean in vision? ›
A -1.75 eyewear prescription essentially signifies that you need some additional power to see some objects that are further away. Specifically, we are talking about things like watching television or objects or people at a distance when you are driving.What is OD and OS for contacts? ›
O.D.- This is oculus dexter, meaning right eye. O.S.- This is oculus sinister, meaning left eye.How do you know your base curve for contacts? ›
- For plus power use the spherical equivalent (SE) and add 4.00 diopters to that. For example, if you have an Rx of + 2.00 sphere, the base curve for the lens will be approximately 6.00.
- Rx +2.00Sph -> [+2.00 +4.00D] = 6.00BC.
If you're legally blind, your vision is 20/200 or less in your better eye or your field of vision is less than 20 degrees. That means if an object is 200 feet away, you have to stand 20 feet from it in order to see it clearly. But a person with normal vision can stand 200 feet away and see that object perfectly.What eyesight is legally blind? ›
Visual acuity less than 20/200 is considered legally blind, but to actually fit the definition, the person must not be able to attain 20/200 vision even with prescription eyewear. Many people who would be legally blind without eyewear can function well in everyday life with appropriate glasses or contact lenses.What is the legally blind prescription? ›
Simply put, if your prescription is -2.5 or lower, this means that you are legally blind. Visual acuity of -2.5 is equivalent to 20/200 vision. Visual acuity of -3.0, for instance, means that you have 20/250 or 20/300 vision. From there, visual acuity of -4.0 means that you have 20/400 vision.What level of astigmatism require glasses? ›
What Level of Astigmatism Requires Glasses? You'll likely need glasses if your astigmatism has a strength of 1.0 or more. But even if your astigmatism needs less than 1.0 diopters of correction, it doesn't mean you won't need glasses.What is the strongest contact prescription? ›
What is the strongest contact lens prescription? Contact lenses can be prescribed for extreme degrees of myopia, even for those who need correction of more than -20 Dioptres. Some lenses can go over -30 Dioptres. For monthly soft contact lenses, the highest level of corrective power is about -12 Dioptres.
For people with extreme nearsightedness, defined as a prescription of -6.0 diopters or more, it may be difficult to see anything more than a foot or so away from the face. In addition to making sight difficult, high myopia can come with severe complications.Why do I see blurry with my contacts? ›
The most common reasons for blurry vision with contacts are an outdated prescription, a new prescription you haven't adjusted to yet, wearing your contacts for too long, contacts that don't fit correctly, and allergies.What happens if you wear contacts with the wrong base curve? ›
Wearing poorly-fitting contact lenses can damage the eye and cause problems such as blurred vision, headaches, and eye strain. The diameter and base curve of a contact lens are two measurements that affect how well they fit your eye.Does base curve have to be exact? ›
The base curve number would be a number between 8.0 and 10.0 millimeters and would be more precise because these lenses need to fit just right. Now that most contact lenses dispensed are soft lenses, this measurement doesn't need to be quite as precise.