Understanding your eye prescription can be confusing, especially with all the abbreviations, numbers, and medical jargon. However, knowing how to read your eye prescription is essential for making informed decisions about your glasses or contact lenses. Whether you're picking out a new pair of glasses, evaluating your vision over time, or simply curious about what those numbers mean, this guide will help you decode your eye prescription with ease.
This article will break down every component of your eye prescription, explain what each term means, and help you determine whether your prescription is expired, if your vision needs are changing, or if it's time for a check-up. We will also cover how contact lens prescriptions differ from glasses prescriptions, and provide real-life examples and data to help you better understand your visual health.
Your Glasses Prescription, Explained
A typical eye prescription includes several abbreviations and numbers that specify the correction needed for each eye. These details are crucial for crafting lenses that provide optimal vision.
Eye Prescription Abbreviations
Here are the most commonly used abbreviations in a glasses eye prescription:
| Abbreviation | Meaning | Description |
| OD | Oculus Dexter | Right Eye |
| OS | Oculus Sinister | Left Eye |
| OU | Oculus Uterque | Both Eyes |
| SPH | Sphere | Indicates the lens power required to correct nearsightedness or farsightedness. |
| CYL | Cylinder | Measures the degree of astigmatism, if any. |
| AXIS | Axis | Refers to the angle of astigmatism correction, ranging from 1 to 180 degrees. |
| ADD | Addition | Extra magnifying power for reading or bifocal lenses. |
| PD | Pupillary Distance | Distance between the centers of your pupils, used to position lenses properly. |
These abbreviations are standardized across most optometrists and optical retailers.
Eye Prescription Scale
The numbers in your eye prescription are measured in diopters (D), which reflect the focusing power needed:
A negative (-) SPH indicates myopia (nearsightedness)
A positive (+) SPH indicates hyperopia (farsightedness)
CYL values show the severity of astigmatism
The higher the number, the stronger the prescription
Example Scale (SPH):
| Diopter (D) | Vision Description |
| 0.00 | Perfect vision |
| -0.25 to -1.00 | Mild myopia |
| -1.25 to -3.00 | Moderate myopia |
| -3.25 to -6.00 | Severe myopia |
| -6.00 and above | High myopia |
Other Terms on Your Eye Prescription
Other helpful terms you might find:
Prism: Corrects eye alignment issues.
Base: Direction of prism correction (Up, Down, In, Out).
NV (Near Vision): Used for reading or close-up tasks.
Distance: Used for everyday activities like driving.
Prescription Expired?
Your eye prescription is not valid indefinitely. In most countries, glasses prescriptions expire within 1 to 2 years, depending on local regulations and your age or health condition. Always check the issue date and validity.
| Country | Prescription Validity |
| USA | 1-2 years |
| UK | 2 years |
| Canada | 1-2 years |
| Australia | 2 years |
Outdated prescriptions can lead to eye strain, headaches, and incorrect vision correction. If your prescription is expired, it's time for a comprehensive eye exam.
Eye Prescription Chart Example
Here is an example of a typical eye prescription:
| Eye | SPH | CYL | AXIS | ADD | PD |
| OD | -2.50 | -0.75 | 180 | +1.75 | 63 |
| OS | -2.00 | -1.00 | 170 | +1.75 | 63 |
Explanation:
The person is nearsighted (negative SPH values).
Has astigmatism in both eyes (CYL values).
Needs reading correction (+1.75 ADD).
PD is 63mm, important for lens alignment.
Is Your Eye Prescription "Bad"?
People often ask: "Is my prescription bad?" The term "bad" is subjective. Here's a breakdown of how prescriptions are typically categorized:
| SPH Value Range | Classification | Vision Without Glasses |
| 0.00 to -1.00 | Mild Myopia | Clear vision at 3-6 feet |
| -1.25 to -3.00 | Moderate Myopia | Blurry beyond 1-2 feet |
| -3.25 to -6.00 | Severe Myopia | Clear only at inches away |
| Over -6.00 | High Myopia | Legally blind without correction |
There's no such thing as a "bad" eye prescription—only one that needs the right correction. Many people with high prescriptions enjoy excellent vision with the right glasses or contacts.
Will Your Eye Prescription Change?
Yes, most people's eye prescription changes over time. Common causes include:
Age: Presbyopia (age-related farsightedness) typically begins after age 40.
Screen time: Excessive device use can strain eyes.
Health conditions: Diabetes, hypertension, and other diseases can affect vision.
Lifestyle changes: Diet, sleep, and exercise can all impact eye health.
Children and teens may experience rapid changes due to growth, while adults usually see more stable prescriptions with gradual age-related shifts.
Due for a check-up?
Experts recommend getting a comprehensive eye exam every 1-2 years, or sooner if you experience:
Regular eye exams help detect early signs of eye diseases like glaucoma, cataracts, and macular degeneration. Also, routine checks ensure your glasses are up-to-date and effective.
What About Contact Lens Prescriptions?
A contact lens prescription is different from a glasses prescription. It includes additional measurements because contacts sit directly on your eye, while glasses sit about 12mm away.
| Measurement | Description |
| Base Curve (BC) | Determines how the lens fits the curvature of your eye |
| Diameter (DIA) | Width of the lens |
| Brand | Specific lens approved for your eye shape and vision needs |
| Power | Similar to SPH, but may differ from your glasses prescription |
Contact lens prescriptions require a separate fitting session. Never use your glasses prescription to buy contacts—it won't provide the right fit or comfort.
Conclusion
Reading your eye prescription is a valuable skill that helps you take control of your vision and overall eye health. Whether you're reviewing your current glasses specs, considering contact lenses, or just checking when you're due for your next exam, understanding the elements of your eye prescription empowers you to make smarter choices.
From abbreviations like SPH, CYL, and PD, to knowing when your prescription is expired, this guide covered everything you need to decode your eye prescription. Remember, regularly updating your glasses and getting routine eye exams are vital steps toward maintaining optimal vision.
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FAQs
Q1: Can I use my glasses prescription for contact lenses?
No. A contact lens prescription includes different measurements like base curve and diameter, which are not in a glasses prescription.
Q2: What does -2.00 mean in my prescription?
It means you are nearsighted and need a lens with -2.00 diopters to correct your distance vision.
Q3: How often should I get my eyes tested?
At least every 1-2 years, or more frequently if you have vision issues or health concerns like diabetes.
Q4: What is PD, and why is it important?
PD stands for Pupillary Distance, crucial for centering your lenses in your glasses for accurate vision correction.
Q5: Is a higher negative number worse vision?
Not necessarily "worse," but it means your eyes need stronger correction. Many people with high prescriptions still see perfectly with the right glasses.
Q6: Can my prescription improve over time?
It's rare but possible. Vision changes due to health, lifestyle, and corrective surgeries can improve or stabilize your eye prescription.
Q7: How do I know if my prescription is expired?
Check the issue date. In most countries, a glasses eye prescription is valid for 1-2 years.
Q8: What does +1.75 ADD mean?
It's an additional magnifying power for reading or close-up tasks, commonly used in bifocals or progressive lenses.
Q9: Are online vision tests accurate?
They can give a general idea but are not a substitute for a professional, in-person eye exam.
Q10: What does axis mean in my prescription?
Axis refers to the angle (1–180 degrees) at which astigmatism correction is applied in your lenses.
By understanding your eye prescription, you're taking proactive steps toward better vision and eye care. Whether you're shopping for new glasses, switching to contacts, or just keeping tabs on your eyesight, knowledge is your best vision tool.
