What Does Your Glasses Prescription Mean? Every Number Explained (Edmonton Optician's Guide)

Written by the Charm Optical Team • April 7, 2026

You just walked out of your eye exam with a piece of paper (or a printout) covered in numbers, abbreviations, and symbols. SPH, CYL, AXIS, ADD, OD, OS. It looks more like a math equation than anything medical. And you're supposed to use this to buy glasses?

You're not alone. This is one of the most common things patients ask about at our Edmonton optical store. They sit down at the dispensing table, hand us the prescription, and say: "So what does all this actually mean?" This guide answers that question in plain English, number by number, so you understand exactly what your glasses prescription is telling you about your eyes.

What Is a Glasses Prescription, Exactly?

A glasses prescription is a set of measurements from your eye exam that describes what your eyes need to see clearly. Your optometrist tests how light focuses inside each eye, then writes down the exact lens power required to correct any issues.

Think of it like a recipe. Each number tells the optical lab how to grind and shape your lenses so they bend light at the right angle for your specific eyes. No two prescriptions are identical, even between your left and right eye.

Every licensed optometrist and ophthalmologist in Alberta follows the same standard format, so your prescription will look similar whether you got it in Ellerslie, Windermere, or downtown Edmonton. The numbers mean the same thing everywhere. The Canadian Association of Optometrists provides a good overview of prescription standards across the country.

OD and OS: Why Your Eyes Get Separate Numbers

The first thing you'll notice on your prescription is two rows: one labelled OD and one labelled OS.

• OD (Oculus Dexter) = your right eye
• OS (Oculus Sinister) = your left eye

These are Latin terms that optometrists have used for centuries. Some newer prescriptions use RE (right eye) and LE (left eye) instead, but OD and OS are still the standard in most Alberta clinics.

Your two eyes almost always have different prescriptions. It's completely normal to be more nearsighted in one eye than the other, or to have astigmatism in just one eye. That's why each eye gets its own row of numbers.

You might also see OU (Oculus Uterque), which means "both eyes." This usually shows up in medical notes rather than on a standard glasses prescription.

SPH (Sphere): The Main Number on Your Glasses Prescription

SPH stands for Sphere, and it's the most important number on your prescription. It measures how much correction your eyes need to bring things into focus. The unit is dioptres (written as "D"), and the number will be either positive (+) or negative (-).

If your SPH is 0.00 or the field is blank, that eye doesn't need correction for distance vision. A small number like -0.50 means you need very mild correction. A larger number like -6.00 means significantly more correction is needed.

SPH corrects for two common conditions:

• Myopia (nearsightedness): You see close objects clearly but distant ones are blurry. SPH will be a minus number (e.g., -2.25).
• Hyperopia (farsightedness): Distant objects may be clear but close-up work is strained. SPH will be a plus number (e.g., +1.50).

The SPH value tells the lab the base curvature to grind into your lens. Everything else on the prescription fine-tunes from there.

Minus vs. Plus: What the Sign on Your Prescription Means

This is one of the parts that confuses people most. That little + or - in front of your numbers isn't just decoration. It fundamentally changes what the lens does.

Minus (-) Prescriptions: Nearsighted (Myopia)

A minus prescription means you're nearsighted. Your eye is slightly too long or the cornea curves too steeply, so light focuses in front of the retina instead of directly on it. The minus lens pushes the focal point back onto the retina.

Common scenario: you can read your phone fine, but road signs are blurry until you're right up close. This is extremely common in Edmonton, especially among young adults and students. The American Academy of Ophthalmology notes that myopia rates have been rising globally, partly linked to increased screen time and reduced outdoor activity.

A prescription of -1.00 to -3.00 is considered mild to moderate myopia. From -3.00 to -6.00 is moderate to high. Anything beyond -6.00 is high myopia, and your optometrist will likely want to monitor you more closely for retinal changes.

Plus (+) Prescriptions: Farsighted (Hyperopia)

A plus prescription means you're farsighted. Your eye is slightly shorter than average or the cornea is flatter, so light focuses behind the retina. The plus lens brings the focal point forward.

Mild farsightedness (like +0.75 or +1.00) often goes unnoticed in younger people because the eye can compensate on its own. But this compensation causes fatigue, especially during long stretches of reading or screen work. Many patients in the Heritage Valley and Summerside areas come in complaining of headaches after work, and it turns out a small plus prescription solves the problem entirely.

CYL and AXIS: The Astigmatism Numbers on Your Edmonton Prescription

CYL stands for Cylinder. AXIS is measured in degrees from 1 to 180. Together, they correct astigmatism.

Astigmatism means your cornea (the clear front surface of your eye) isn't perfectly round. Instead of being shaped like a basketball, it's more like a rugby ball. Light entering the eye hits at different angles, creating two focal points instead of one. The result: blurry or distorted vision at all distances.

What CYL Tells You

The CYL number measures the amount of astigmatism. Like SPH, it's measured in dioptres and can be negative or positive (depending on the notation style your doctor uses). A CYL of -0.50 is very mild. A CYL of -2.50 or beyond is significant and will noticeably affect your vision if uncorrected.

If your CYL field is blank or shows 0.00, you don't have astigmatism in that eye. No cylinder correction needed.

What AXIS Tells You

AXIS is a number between 1 and 180 that indicates the angle of your astigmatism. Think of it as the compass direction where the irregular curvature sits on your cornea. An axis of 90 means the curvature is vertical. An axis of 180 means it's horizontal.

AXIS only appears when there's a CYL value. Without astigmatism, there's no angle to specify. When filling your prescription, the lab must get this angle exactly right. Even a few degrees off can cause the lens to feel uncomfortable or not correct your vision fully.

About one in three Canadians has some degree of astigmatism. Most cases are mild and easily corrected with glasses. If you've been told you have astigmatism and it sounds intimidating, it really isn't. It's one of the most routine things we correct at our Ellerslie location.

ADD Power: When You Need Progressives in Edmonton

ADD (short for Addition) is the extra magnifying power added to the bottom portion of your lenses so you can read up close. It's always a positive number, typically ranging from +0.75 to +3.00.

You'll only see an ADD value on your prescription if you have presbyopia, the age-related loss of near focusing ability. Presbyopia is not a disease. It happens to everyone, usually starting in the early-to-mid forties, and gradually increases until about age 65.

How ADD Power Works

Your SPH and CYL correct your distance vision. The ADD value is layered on top to create a separate zone for reading and close-up tasks. That's how progressive lenses and bifocals work: the top of the lens handles distance, and the bottom handles near vision, with the ADD power providing the boost.

A typical progression looks like this:

• Age 42-45: ADD starts around +0.75 to +1.00 (you notice menus getting harder to read)
• Age 45-50: ADD increases to +1.25 to +1.75
• Age 50-55: ADD reaches +1.75 to +2.25
• Age 55-65: ADD plateaus around +2.25 to +3.00

If you have an ADD value on your prescription, you'll need either progressive lenses, bifocals, or dedicated reading glasses. At Charm Optical, our progressive lenses start at $350 (frame + lenses), and we'll walk you through which option makes sense for your daily activities.

The ADD number is the same for both eyes in the vast majority of prescriptions. It's rare for a doctor to prescribe different ADD values for OD and OS.

PD (Pupillary Distance): The Measurement Your Lab Needs

PD stands for Pupillary Distance. It's the distance in millimetres between the centres of your two pupils. This measurement tells the lab exactly where to position the optical centre of each lens so it lines up with your eyes.

Average PD for adults ranges from about 54mm to 74mm. Children typically fall between 43mm and 58mm.

Single PD vs. Dual PD

Your PD may be written as a single number (e.g., 63mm) or as two numbers (e.g., 31/32). The dual PD is more precise because most people's faces aren't perfectly symmetrical. The right eye might be 31mm from the centre of your nose while the left is 32mm.

For single vision glasses, a single PD usually works fine. For progressive lenses, a dual PD (also called monocular PD) is strongly recommended because the reading zone needs to align precisely with each pupil.

Why PD Matters

If the optical centres of your lenses don't line up with your pupils, you'll experience eyestrain, headaches, and blurry peripheral vision. The stronger your prescription, the more sensitive it is to PD accuracy. A patient with -1.00 SPH might tolerate a PD that's off by 2mm. A patient with -6.00 would notice immediately.

Some optometrists include PD on the prescription itself. Others don't, because technically PD is a fitting measurement, not a clinical finding. If your prescription doesn't include PD, any optical store can measure it for you. At Charm Optical, we measure PD as part of every fitting, whether you got your prescription from us or brought one in from another clinic.

Glasses Prescription Terms Explained (Quick Reference Table)

Here's every abbreviation and number you might see on your glasses prescription, explained in one place:

Term	Full Name	What It Means	Typical Range
OD	Oculus Dexter	Right eye	N/A
OS	Oculus Sinister	Left eye	N/A
SPH	Sphere	Main lens power; corrects nearsightedness (-) or farsightedness (+)	-20.00 to +20.00 D
CYL	Cylinder	Amount of astigmatism correction	-0.25 to -6.00 D
AXIS	Axis	Angle (in degrees) where astigmatism correction is applied	1 to 180°
ADD	Addition	Extra magnification for reading; indicates need for progressives or bifocals	+0.75 to +3.50 D
PD	Pupillary Distance	Distance between your pupils; used to centre the lenses	43 to 74 mm
Prism	Prism	Corrects eye alignment issues (double vision); less common	0.25 to 10.00 Δ

Sample Glasses Prescription: Reading a Real Example

Let's walk through a realistic prescription for a 48-year-old patient in Edmonton who needs both distance correction and reading help. Here's what their prescription might look like:

Eye	SPH	CYL	AXIS	ADD	PD
OD (Right)	-2.25	-0.75	170	+1.50	31
OS (Left)	-1.75	-1.25	015	+1.50	32

Here's what each number means for this patient:

• SPH -2.25 / -1.75: Both eyes are nearsighted (minus sign). The right eye needs slightly more correction than the left. This is moderate myopia. Distance vision is blurry without glasses.
• CYL -0.75 / -1.25: Both eyes have astigmatism. The left eye has more (-1.25) than the right (-0.75). The left lens will have a more complex curvature.
• AXIS 170 / 015: The astigmatism sits at different angles in each eye. The right eye's correction is nearly horizontal (170°), while the left is nearly vertical (15°).
• ADD +1.50: This patient is in the early stages of presbyopia. They need +1.50 dioptres of extra power for reading. Progressive or bifocal lenses are needed.
• PD 31/32: Dual PD measurement. Right pupil is 31mm from centre, left is 32mm. Total PD is 63mm.

With this prescription, we'd recommend progressive lenses. The patient gets clear distance vision through the top of the lens, smooth intermediate vision (computer distance) in the middle, and full reading correction at the bottom, all in one pair of glasses.

Is My Prescription Strong? Understanding Your Numbers in Edmonton

One of the first things patients ask after their eye exam is, "Is this a strong prescription?" Here's a general guideline for SPH values:

• Mild: -0.25 to -2.00 (or +0.25 to +2.00)
• Moderate: -2.25 to -5.00 (or +2.25 to +5.00)
• High: -5.25 to -8.00 (or +5.25 to +8.00)
• Very high: Beyond -8.00 or +8.00

Stronger prescriptions affect your lens options. With a mild prescription, almost any frame works and the lenses stay thin. With a high prescription, you'll want to consider high-index lenses (thinner, lighter material) and avoid oversized frames that make thick edges more visible.

If your prescription is above -6.00, your optometrist will likely recommend more frequent eye exams. High myopia increases the risk of retinal detachment and other conditions, so regular monitoring matters. We see this often with university students and tech workers in the Walker and Rutherford areas who spend long hours on screens.

CYL strength matters too. Astigmatism above -2.00 CYL is considered significant and can make you more sensitive to how your glasses sit on your face. Proper frame fitting becomes more important.

What Lens Type Do You Need? Single Vision vs. Progressive in Edmonton

Your prescription determines which lens type you need. The key indicator is whether you have an ADD value.

Single Vision Lenses (No ADD on Prescription)

If your prescription only has SPH (and possibly CYL/AXIS) but no ADD value, you need single vision lenses. These correct for one distance only: either far away or up close.

Single vision is the most common lens type for people under 40. At Charm Optical, complete single vision glasses (frame + lenses) start at $55 with our Momono collection. You can also bring your own prescription and browse our full frame selection including Ray-Ban, Oakley, Gucci, and more.

Progressive Lenses (ADD Value Present)

If your prescription includes an ADD value, you need multifocal lenses. Most people choose progressives over traditional bifocals because there's no visible line on the lens, and you get a smooth transition between distance, intermediate, and near vision.

Progressive lenses start at $350 complete (frame + progressive lenses) at Charm Optical. Premium progressives with wider reading corridors and less peripheral distortion are available for patients who need them, particularly those working on computers all day in offices around South Edmonton and Windermere.

For a detailed comparison, read our guide on progressive lenses vs. bifocals.

How Long Is a Glasses Prescription Valid in Alberta?

In Alberta, a glasses prescription is typically valid for two years from the date of your exam. After that, you'll need a new eye exam before an optical store can fill a new pair of glasses.

There are some exceptions. If your optometrist determines your eyes are changing more rapidly (common in children, diabetics, and patients with high myopia), they may issue a prescription valid for only one year. The expiry date should be noted on your prescription.

The Canadian Association of Optometrists recommends eye exams every one to two years for most adults, and annually for children and seniors. Even if your prescription hasn't changed, the eye health portion of the exam can catch conditions like glaucoma or macular degeneration early.

At Charm Optical, a comprehensive eye exam is $99. For children under 19 and seniors 65 and older, Alberta Health covers the exam. You can book your eye exam online at see.charmoptical.ca.

Where to Fill Your Glasses Prescription Near Me in Edmonton

If you're looking for a place to fill your glasses prescription in Edmonton, you want an optical store that takes the time to measure your PD accurately, helps you choose the right frame for your face shape and prescription strength, and explains your lens options without upselling you on things you don't need.

Charm Optical is located at 5035 Ellerslie Rd SW, Edmonton, AB T6X 1X2, in the Ellerslie area of south Edmonton. We serve patients from across the city, with many coming from Heritage Valley, Summerside, Walker, Rutherford, Callaghan, Orchards, and Windermere.

Whether you got your prescription from our in-house optometrist or from another clinic, you're welcome to bring it in. We fill prescriptions from any licensed optometrist or ophthalmologist in Alberta.

What to Bring

• Your written or printed glasses prescription (make sure it's less than 2 years old)
• Your insurance card (if applicable)
• Your current glasses, if you have them (helps us compare)

Give us a call at (780) 490-0090 if you have questions about your prescription before coming in. We're happy to look at it over the phone and help you understand what you need.

Using Insurance for Glasses in Edmonton

Most employer-sponsored insurance plans in Alberta include some coverage for prescription eyewear, typically every 24 months. Coverage amounts vary widely, from $150 to $500 or more per person depending on your plan.

At Charm Optical, we direct bill the following insurance providers:

• Alberta Blue Cross
• Canada Life (formerly Great-West Life)
• Desjardins
• AISH (Assured Income for the Severely Handicapped)
• Alberta Works

Direct billing means we submit the claim for you while you're still in the store. You only pay the difference between your coverage and the total cost. No receipts to submit, no waiting for reimbursement.

If your insurance plan isn't listed above, you can still purchase from us and submit the receipt to your provider for reimbursement. We provide all the documentation you need, including your prescription details and itemized receipt.

Frequently Asked Questions About Glasses Prescriptions

Can I use my glasses prescription to buy contact lenses?

No. A glasses prescription and a contact lens prescription are different. Contact lenses sit directly on your eye, so they require additional measurements including base curve and diameter. You'll need a separate contact lens fitting from your optometrist. The SPH, CYL, and AXIS values are often different between the two prescriptions as well.

What does it mean if my glasses prescription changed?

Prescription changes are normal, especially for children, young adults, and people over 40. A change of 0.25 to 0.50 dioptres between exams is common and nothing to worry about. Larger changes may warrant more frequent monitoring. If your prescription changed significantly, your optometrist will discuss why and whether additional testing is needed.

Why does my prescription have different numbers for each eye?

Your two eyes develop independently and rarely have identical optical properties. One eye might be more nearsighted, have more astigmatism, or age differently than the other. This is completely normal. Your optometrist measures each eye separately to give you the most accurate correction for both.

Do I need progressive lenses if I have an ADD value?

If your prescription includes an ADD value, you need some form of multifocal correction for comfortable near vision. Progressive lenses are the most popular option because they provide distance, intermediate, and near vision without a visible line. Bifocals are an alternative. Some patients opt for separate distance and reading glasses instead. Your optician can help you decide based on your daily activities and budget. At Charm Optical, progressives start at $350 complete.

What is a high prescription for glasses?

Generally, an SPH value beyond -6.00 or +6.00 is considered a high prescription. High prescriptions benefit from high-index lens materials that keep the lenses thinner and lighter. Frame selection also matters more with strong prescriptions, as smaller frames reduce edge thickness and weight. Our team at Charm Optical can recommend the best frame and lens combination for higher prescriptions.

Can I get glasses the same day in Edmonton?

Simple single vision prescriptions with standard lenses can sometimes be ready the same day, depending on the lens type and stock. Most glasses take a few business days because the lenses are custom-cut to your prescription. Progressive lenses and high-index lenses typically take longer. Ask us about current turnaround times when you visit our Ellerslie location or call (780) 490-0090.

Is my glasses prescription the same as my eye exam results?

Not exactly. Your eye exam includes many tests beyond the prescription: eye pressure, retinal health, peripheral vision, and more. The prescription is just one part of the exam. It's the optical correction portion that tells you (and us) what lenses you need. The rest of the exam evaluates your overall eye health.