An eye prescription is a written set of measurements that tells an optometrist or optical professional what lens power is needed to correct your vision.
If you have ever looked at a glasses prescription and wondered what OD, OS, SPH, CYL, AXIS, ADD, or PD mean, you are not alone. These numbers and abbreviations can look confusing at first.
You may see your eye prescription on a paper from an eye exam, on a glasses order, or in an online eyewear account.
Understanding it can help you order glasses correctly, compare prescriptions, and know what your vision correction is designed to do.
The important point is that an eye prescription is not simply a score for how good or bad your eyesight is. It contains several measurements, and each one describes a different part of your vision correction.
Quick Answer
| Term | Meaning |
|---|---|
| Eye prescription | Measurements used to specify the lens correction needed for your eyes |
| OD | Right eye |
| OS | Left eye |
| OU | Both eyes |
| SPH / Sphere | Main lens power for nearsightedness or farsightedness |
| CYL / Cylinder | Amount of astigmatism correction |
| AXIS | Direction of astigmatism correction, measured from 1–180° |
| ADD | Extra lens power for near vision, commonly used in multifocal lenses |
| PRISM | Correction used in some prescriptions for certain eye alignment problems |
| PD | Pupillary distance, the distance between the pupils |
| Plano / PL | No spherical lens power |
| Plus (+) | Usually indicates farsighted correction or added positive lens power |
| Minus (−) | Usually indicates nearsighted correction |
| Unit | Most lens powers are measured in diopters |
| Purpose | To tell the optical professional what lens specifications to use |
In simple terms: your eye prescription tells you how much and what type of lens correction each eye needs.
What Does Eye Prescription Mean?
The phrase eye prescription usually refers to the measurements written by an eye-care professional after an eye examination. These measurements are used to make prescription glasses or contact lenses that correct refractive errors.
A prescription may contain several different values because vision problems are not all the same.
For example, one person may simply be nearsighted and need a spherical lens power. Another person may be nearsighted and have astigmatism, requiring sphere, cylinder, and axis measurements.
Someone who needs help seeing both far away and up close may also have an ADD value for multifocal correction.
A typical glasses prescription might look something like this:
| SPH | CYL | AXIS | |
|---|---|---|---|
| OD | -2.00 | -0.75 | 90 |
| OS | -1.50 | -0.50 | 80 |
This does not mean the right eye is simply “worse” than the left. It means the two eyes have different correction requirements.
The prescription is also different from a visual acuity result such as 20/20. Visual acuity describes how clearly you can see under a particular testing condition. A prescription describes the lens correction used to improve refractive focus.
Understanding the Main Parts of an Eye Prescription
The easiest way to read an eye prescription is to understand each abbreviation separately.
OD: Right Eye
OD comes from the Latin term oculus dexter, meaning right eye.
If your prescription has an OD column, those numbers apply to your right eye.
OS: Left Eye
OS comes from oculus sinister, meaning left eye.
The OS values apply to your left eye.
Despite the words “dexter” and “sinister,” these are simply traditional medical abbreviations. They do not mean anything negative about the eye.
OU: Both Eyes
OU comes from oculus uterque, meaning both eyes.
You may see OU used when a measurement or instruction applies to both eyes.
What Does SPH Mean on an Eye Prescription?
SPH, short for sphere, is one of the most important numbers on a glasses prescription.
It indicates the main amount of spherical lens power needed to correct refractive error.
The number is usually written with a plus (+) or minus (−) sign and is measured in diopters (D).
A minus SPH value
A negative sphere value, such as:
- -0.50
- -1.25
- -3.00
- -5.00
generally indicates correction for nearsightedness, also called myopia.
With myopia, distant objects may appear blurry without correction.
A plus SPH value
A positive sphere value, such as:
- +0.50
- +1.00
- +2.00
generally indicates farsighted correction, or hyperopic correction.
A positive power can also appear as part of a near-vision or multifocal prescription, so the number should always be interpreted in context.
What does 0.00 or Plano mean?
If SPH is written as 0.00, 0, or PL/Plano, it generally means there is no spherical correction for that eye.
That does not necessarily mean the entire prescription has no correction. An eye could have no spherical power but still have astigmatism correction.
What Does CYL Mean on an Eye Prescription?
CYL means cylinder.
It indicates the amount of lens power used to correct astigmatism.
Astigmatism occurs when the eye’s optical system has an irregular curvature, causing light to focus differently in different directions. It can contribute to blurry or distorted vision at various distances.
A CYL value may look like:
- -0.50
- -1.00
- -1.75
- +0.75
The sign depends on the prescription format or notation being used.
A cylinder value cannot be interpreted by itself. It works together with the AXIS value.
What Does AXIS Mean on an Eye Prescription?
AXIS tells you the orientation of the cylinder correction used for astigmatism.
It is written as a number between 1 and 180 degrees.
For example:
- 10°
- 45°
- 90°
- 135°
- 180°
The axis is not an amount of prescription strength.
This is a common misunderstanding.
If a prescription says:
CYL -1.00, AXIS 90
the -1.00 describes the cylinder power, while 90 describes its orientation.
Think of it this way:
- CYL = how much astigmatism correction
- AXIS = which direction that correction is positioned
Both are needed when cylinder correction is prescribed.
What Does ADD Mean on an Eye Prescription?
ADD means additional power.
It is commonly used in prescriptions for multifocal lenses, such as bifocals or progressive lenses.
The ADD value represents extra lens power intended to help with near vision.
For example, you might see:
ADD +2.00
This does not necessarily mean your entire prescription is +2.00. Instead, it indicates additional power for the near portion of a multifocal lens.
ADD values are often associated with presbyopia, an age-related change in the eye’s ability to focus on nearby objects.
If you have a single-vision distance prescription, you may not have an ADD value at all.
What Does PD Mean on an Eye Prescription?
PD means pupillary distance.
It is the distance between the centers of your pupils, usually measured in millimeters.
For example, a prescription might list:
PD: 62 mm
PD is important because the optical center of a lens needs to line up appropriately with the wearer’s pupils.
Some prescriptions provide one total PD measurement, while others provide separate measurements for each eye, such as:
- Right: 31 mm
- Left: 31 mm
This is sometimes called monocular PD.
Is PD part of the prescription?
It depends on the prescription and how it was issued. In some situations, PD is recorded separately from the clinical prescription.
This distinction matters when ordering glasses because an optical professional may need additional measurements beyond the basic lens powers.
What Does Prism Mean on an Eye Prescription?
Some prescriptions include a section labeled PRISM and BASE.
Prism is used in certain situations involving how the eyes work together or how they are aligned.
A prism prescription may contain:
- Prism amount
- Base direction
Base direction can be described using terms such as:
- Base up
- Base down
- Base in
- Base out
Prism is different from ordinary spherical or cylinder power. If your prescription includes prism, it is especially important to have the lenses made according to the complete prescription rather than trying to interpret or modify the numbers yourself.
Why Are Eye Prescriptions Different for Each Eye?
It is completely normal for the right and left eyes to have different prescriptions.
For example:
| Right Eye | Left Eye | |
|---|---|---|
| SPH | -2.00 | -1.25 |
| CYL | -0.75 | -0.50 |
| AXIS | 90 | 80 |
The eyes do not always have identical focusing characteristics.
One eye may be more nearsighted than the other. One may have more astigmatism. One eye may require a different axis.
This is one reason you should not assume that the prescription for one eye can be copied to the other.
What Do Plus and Minus Numbers Mean?
The + and − signs are important.
A negative spherical power generally indicates correction for myopia, or nearsightedness.
A positive spherical power generally indicates correction for hyperopia, or farsightedness.
However, a prescription is more than one number. A person may have:
- Plus sphere with cylinder
- Minus sphere with cylinder
- Plano sphere with cylinder
- A multifocal ADD
- Prism correction
So it is not accurate to judge someone’s complete eye prescription simply by looking at whether it contains a plus or minus sign.
What Does the Strength of an Eye Prescription Mean?
Lens power is measured in diopters.
In general, a larger absolute number represents a stronger lens power.
For example, -4.00 D has more spherical power than -1.00 D.
But “stronger prescription” does not automatically mean “worse eyes.”
A glasses prescription describes optical correction. It does not provide a complete assessment of eye health.
Someone can have a strong prescription and healthy eyes, while someone with a mild prescription can still have an eye-health problem that requires medical attention.
That is why an eye examination involves more than simply determining the glasses prescription.
Eye Prescription vs. Visual Acuity
These terms are often confused.
Eye prescription
Your prescription specifies the lens power and other measurements used for corrective lenses.
Visual acuity
Visual acuity describes how clearly you can identify details at a particular distance during a vision test.
For example, 20/20 is a visual acuity measurement.
These are not interchangeable.
You can have a prescription and achieve good corrected visual acuity with glasses. You can also have relatively good visual acuity while still needing correction in particular situations.
A prescription number does not directly translate into a simple “eyesight percentage.”
Eye Prescription vs. Contact Lens Prescription
A glasses prescription and a contact lens prescription are not always interchangeable.
Contact lenses sit directly on the eye, while glasses sit in front of the eye. Contact lens prescriptions can therefore include information that is not normally needed for ordinary glasses, such as:
- Brand or lens type
- Base curve
- Diameter
- Lens power
- Other fitting information
For stronger prescriptions, the difference between glasses and contact lens power can also become more important because the lenses sit at different distances from the eye.
If you want contact lenses, you generally need an appropriate contact lens fitting and prescription rather than simply entering your glasses numbers into a contact lens order form.
How People Use an Eye Prescription
You usually encounter an eye prescription in practical situations rather than everyday conversation.
Common uses include:
- Buying new glasses
- Replacing broken glasses
- Ordering prescription eyewear online
- Comparing an old and new prescription
- Checking whether your prescription has changed
- Discussing vision correction with an optical professional
- Understanding your eye-exam paperwork
When ordering glasses, you may be asked to enter each value exactly as it appears.
For example, a form may ask separately for:
- Right eye SPH
- Right eye CYL
- Right eye AXIS
- Left eye SPH
- Left eye CYL
- Left eye AXIS
- ADD
- PD
Do not remove the plus or minus signs unless the ordering system specifically instructs you to do so.
How to Read an Eye Prescription Step by Step
If you have your prescription in front of you, use this basic approach.
Step 1: Find OD and OS
Identify which numbers belong to the right eye and which belong to the left.
Step 2: Find SPH
Look for SPH, Sphere, or a similar label.
This is the primary spherical lens power.
Step 3: Check CYL
If there is a cylinder value, it indicates astigmatism correction.
Step 4: Check AXIS
If CYL is present, look for its corresponding axis.
Step 5: Look for ADD
If you have a multifocal prescription, check for an ADD value.
Step 6: Check for PRISM
If prism is listed, pay attention to both the amount and base direction.
Step 7: Check PD separately
Look for pupillary distance if you are ordering glasses and the measurement has been provided.
Step 8: Confirm the signs
A +1.00 and a -1.00 are not interchangeable.
Step 9: Use the complete prescription
Do not choose a lens based on SPH alone if your prescription also contains cylinder, axis, ADD, prism, or other required measurements.
Meaning of an Example Eye Prescription
Consider this fictional prescription:
| Eye | SPH | CYL | AXIS |
|---|---|---|---|
| OD | -2.00 | -1.00 | 90 |
| OS | -1.50 | -0.50 | 80 |
Here is what it tells you:
- OD -2.00 SPH: the right eye has a -2.00 spherical correction.
- OD -1.00 CYL: the right eye also has cylinder correction.
- OD AXIS 90: the cylinder correction is oriented at 90 degrees.
- OS -1.50 SPH: the left eye has a -1.50 spherical correction.
- OS -0.50 CYL: the left eye has a smaller cylinder correction.
- OS AXIS 80: the left cylinder correction is oriented at 80 degrees.
The important lesson is that every part works together. You cannot correctly reproduce this prescription by using only the sphere values.
Eye Prescription Meaning on Different Platforms
Unlike internet slang, eye prescription does not have a special meaning on different social media platforms.
Its meaning remains essentially the same on:
Someone might send a photo of their prescription to a family member, friend, or optical professional and ask what the numbers mean.
The term may appear in posts or captions about glasses, eyesight, eye exams, or eyewear.
TikTok
People may discuss their prescription strength, new glasses, blurry vision, or experiences with eye exams.
Users may ask for help understanding abbreviations on an eye prescription or discuss getting new glasses.
Text Messages
A person might say, “I got my new eye prescription today,” meaning the measurements given after an eye examination.
Online Eyewear Stores
This is one of the most practical places to encounter prescription terminology. An order form may ask for SPH, CYL, AXIS, ADD, and PD.
The terminology itself does not change simply because it appears on a particular platform.
Real-Life Examples of People Talking About Eye Prescriptions
Example 1
Person A: “What does -2.00 mean on my eye prescription?”
Person B: “That’s the sphere power for that eye.”
Why it matters: The person is asking about a specific lens-power value, not a general eyesight score.
Example 2
Person A: “My right eye is -1.50 and my left is -0.75. Is that normal?”
Person B: “It’s common for the two eyes to have different prescriptions.”
Why it matters: Prescriptions do not need to match between eyes.
Example 3
Person A: “What does CYL mean?”
Person B: “It refers to cylinder power used for astigmatism correction.”
Why it matters: CYL describes a different type of correction from sphere power.
Example 4
Person A: “My prescription says AXIS 90. Is that how strong my glasses are?”
Person B: “No. Axis describes the orientation of the cylinder correction.”
Why it matters: Axis is not a measurement of prescription strength.
Example 5
Person A: “Why does my prescription have ADD +2.00?”
Person B: “That is extra power for near vision, often used in multifocal lenses.”
Why it matters: ADD is additional near-vision power rather than simply replacing the distance prescription.
Example 6
Person A: “My prescription says PL for sphere. Does that mean I don’t need glasses?”
Person B: “Not necessarily. You could still have another correction, such as cylinder power.”
Why it matters: One prescription field cannot always be interpreted independently.
Example 7
Person A: “Is my eye prescription the same thing as 20/20?”
Person B: “No. 20/20 is visual acuity; a prescription specifies lens correction.”
Why it matters: These are two different measurements.
Example 8
Person A: “Can I use my glasses prescription for contacts?”
Person B: “Don’t assume they are interchangeable. Contact lenses require their own fitting and prescription information.”
Why it matters: Contact lenses sit directly on the eye.
Example 9
Person A: “Where do I find my PD?”
Person B: “Check whether your prescription or optical paperwork lists pupillary distance.”
Why it matters: PD may be recorded separately depending on the eye-care provider and ordering process.
Example 10
Person A: “My new prescription is different from my old one. Does that mean something is wrong?”
Person B: “A prescription can change over time. Your eye-care professional can explain what changed and why.”
Why it matters: A change in lens power does not, by itself, tell you whether there is an eye-health problem.
When Should You Use the Term “Eye Prescription”?
The phrase is useful whenever you are talking about the lens measurements provided after an eye examination.
For example:
- “I need to update my eye prescription.”
- “Can you explain my eye prescription?”
- “My eye prescription changed.”
- “I need my prescription to order new glasses.”
- “What’s the difference between my old and new eye prescription?”
In everyday English, glasses prescription is also very common when the discussion is specifically about eyeglasses.
If you are talking about the examination itself, eye exam or vision test may be more appropriate.
When Should You Avoid Confusing an Eye Prescription With an Eye Diagnosis?
An eye prescription is not a complete medical diagnosis.
It mainly describes optical correction.
For example, knowing that someone has a -3.00 sphere value does not tell you everything about:
- The health of the retina
- The optic nerve
- Eye pressure
- The cornea
- The overall health of the eye
- Other medical conditions affecting vision
A prescription can tell you what lens correction was prescribed, but it should not be treated as a complete report of eye health.
If your vision changes suddenly, you have sudden vision loss, significant eye pain, flashes or a sudden increase in floaters, or another concerning symptom, seek prompt professional medical evaluation rather than relying on the prescription alone.
Is an Eye Prescription Good, Bad, Strong, or Weak?
People often ask whether a prescription is “good” or “bad.”
That is not the most useful way to think about it.
A prescription is better understood as a measurement of the optical correction needed.
The numerical power can be described as relatively low, moderate, or high in an optical context, but the prescription itself does not determine overall eye health.
For example, someone might say:
“My prescription is really strong.”
Usually, they mean their glasses require relatively high lens power.
That does not automatically mean their eyes are unhealthy.
Other Meanings of “Prescription”
The word prescription can have a broader meaning outside eye care.
In medicine, a prescription is an authorized instruction for a treatment or medication.
In the phrase eye prescription, however, it normally means the set of measurements used to specify vision correction.
So when someone asks, “What does my eye prescription mean?” they are usually asking how to interpret the numbers and abbreviations on their glasses prescription.
There is no special slang or hidden internet meaning attached to the phrase.
Similar Terms and Related Abbreviations
| Term | Meaning | Typical Use | Tone |
|---|---|---|---|
| Eye prescription | Measurements for vision correction | General conversation | Neutral |
| Glasses prescription | Prescription for eyeglass lenses | Eyewear | Neutral |
| Contact lens prescription | Prescription and fitting information for contacts | Contact lenses | Neutral |
| OD | Right eye | Prescription | Medical/technical |
| OS | Left eye | Prescription | Medical/technical |
| OU | Both eyes | Prescription | Medical/technical |
| SPH | Sphere power | Main lens correction | Technical |
| CYL | Cylinder power | Astigmatism correction | Technical |
| AXIS | Orientation of cylinder correction | Astigmatism | Technical |
| ADD | Additional near power | Multifocal lenses | Technical |
| PD | Pupillary distance | Eyeglass fitting | Technical |
| 20/20 | Visual acuity notation | Vision testing | Medical/general |
These terms are related, but they are not interchangeable.
Common Mistakes When Reading an Eye Prescription
Mistake 1: Thinking the prescription is a percentage
A prescription such as -2.00 is not “2% eyesight.”
Diopters and percentages measure different things.
Mistake 2: Ignoring the plus or minus sign
+2.00 and -2.00 represent different lens powers.
Always enter the sign exactly as provided.
Mistake 3: Treating AXIS as strength
Axis is an orientation measurement for cylinder correction. It is not the same as lens power.
Mistake 4: Reading CYL without AXIS
Cylinder and axis work together. If a prescription contains both, both values matter.
Mistake 5: Assuming both eyes have the same prescription
The right and left eyes can have different values.
Mistake 6: Thinking 20/20 is a prescription
20/20 describes visual acuity. It is not the same thing as a glasses prescription.
Mistake 7: Assuming a glasses prescription is automatically a contact lens prescription
Contact lenses require different fitting considerations because they sit directly on the eye.
Mistake 8: Assuming a stronger prescription means worse eye health
Lens power and eye health are related to vision correction but are not the same measurement.
Mistake 9: Guessing missing numbers
If a prescription is unclear, don’t guess whether a value is + or −, or whether an axis is 80 or 90.
A single transcription error can result in incorrectly made glasses.
Mistake 10: Using an old prescription indefinitely
Prescriptions can change. If your vision no longer feels adequately corrected, follow up with an eye-care professional rather than assuming an old prescription is still appropriate.
Frequently Asked Questions
What does an eye prescription tell you?
It tells you the lens correction prescribed for your eyes. Depending on your needs, it can include sphere, cylinder, axis, add power, prism, and other measurements.
What does OD and OS mean on a glasses prescription?
OD means right eye, while OS means left eye. They come from traditional Latin medical terminology.
What does SPH mean on a prescription?
SPH means sphere. It describes the main spherical lens power used to correct refractive error such as myopia or hyperopia.
What does CYL mean in an eye prescription?
CYL means cylinder and represents the amount of astigmatism correction in the prescription.
What does AXIS mean in glasses?
AXIS specifies the orientation of the cylinder correction for astigmatism. It is expressed as a value from 1 to 180 degrees.
What does ADD mean on an eye prescription?
ADD means additional lens power, usually for near vision in bifocal, trifocal, or progressive lenses.
What does PD mean on a glasses prescription?
PD means pupillary distance, the distance between the centers of your pupils. It helps position the lenses correctly.
Is a -2.00 prescription considered bad eyesight?
A -2.00 spherical prescription indicates a particular amount of myopic lens correction. It should not be interpreted as a simple measure of overall eye health.
Can two people have the same eye prescription?
Yes. Different people can have identical or very similar prescriptions. However, prescriptions can also differ considerably from one person to another and between the two eyes of the same person.
Can I understand my prescription without an eye doctor?
You can understand many of the abbreviations and numbers yourself, but an eye-care professional is the right person to explain unusual findings, changes in your prescription, or questions about your eye health.
Final Thoughts
The simplest eye prescription meaning is: a set of measurements that tells an optical professional what lens correction your eyes need.
The most important terms to remember are:
- OD = right eye
- OS = left eye
- SPH = main spherical lens power
- CYL = astigmatism correction
- AXIS = direction of cylinder correction
- ADD = extra near-vision power
- PD = pupillary distance
- PRISM = specialized correction used in some prescriptions
The numbers can look complicated, but each one has a specific job. The key is to read the prescription as a complete set rather than focusing on one number in isolation.
If you are ordering glasses, copy the prescription carefully, including every plus or minus sign, and use the measurements exactly as provided.
If something is unclear or seems inconsistent, ask your optometrist, ophthalmologist, or optical professional rather than guessing.
I am Lily Anderson, an English language writer passionate about explaining word meanings, vocabulary, grammar, pronunciation, and language usage through clear, accurate, and easy-to-understand educational content for learners worldwide.
