- Medically Reviewed by Mr Mfazo Hove Consultant Ophthalmologist
- Author: Chris Dunnington
- Published: January 23, 2025
At Blue Fin Vision® Eye Clinic in London, we believe that empowering our patients with knowledge is crucial for maintaining optimal eye health. One of the most important documents you’ll receive after an eye examination is your prescription. But what do all those numbers and abbreviations mean? In this comprehensive guide, we’ll demystify your eye prescription, helping you understand the key figures and terms that are essential for your vision care.
Your Glasses Prescription Explained
An eye prescription is a vital document provided by your optometrist or ophthalmologist after a thorough eye examination. It contains crucial information about the type and strength of vision correction you need. Understanding your prescription can help you make informed decisions about your eyewear and overall eye health.
The Basics of an Eye Prescription
Your prescription typically includes separate measurements for your right eye (often abbreviated as RE or OD) and left eye (LE or OS). Here’s a breakdown of the key components:
SPH (Sphere)
The SPH value indicates the power of the lens needed to correct your vision. It’s measured in dioptres and is preceded by either a plus (+) or minus (-) sign:
- Plus (+): Indicates long-sightedness (hyperopia)
- Minus (-): Indicates short-sightedness (myopia)
The higher the number, the stronger the prescription.
CYL (Cylinder) and AXIS
These values are related to astigmatism, a condition where the eye isn’t perfectly spherical:
- CYL: Measures the degree of astigmatism
- AXIS: Indicates the orientation of the astigmatism, measured in degrees from 0 to 180
ADD (Addition)
This figure is relevant for those who need multifocal lenses, such as bifocals or varifocals. It represents the additional magnifying power needed for near vision tasks.
PD (Pupillary Distance)
While not always included on the prescription, the PD is crucial for properly centring your lenses. It measures the distance between your pupils.
How to Read an Eye Prescription
Now that we’ve covered the basics, let’s dive deeper into how to interpret these values:
Understanding the Numbers
- SPH (Sphere):
- A -2.00 SPH means you’re short-sighted and need a lens with 2 dioptres of corrective power
- A +1.50 SPH indicates long-sightedness requiring 1.5 dioptres of correction
- CYL (Cylinder):
- The higher the number, the more significant the astigmatism
- For example, -1.25 CYL indicates moderate astigmatism
- AXIS:
- This number ranges from 0 to 180 degrees
- It specifies where on the lens the astigmatism correction should be placed
- ADD:
- Typically ranges from +0.75 to +3.00
- A higher number indicates a stronger magnification needed for near vision
Reading the Prescription Chart
Your prescription might be written out in a format like this:
RE: -2.00 / -0.75 x 180 ADD +1.00
LE: -1.75 / -0.50 x 175 ADD +1.00
Let’s break this down:
For the Right Eye (RE):
- SPH (Sphere): -2.00
- CYL (Cylinder): -0.75
- AXIS: 180
- ADD: +1.00
For the Left Eye (LE):
- SPH (Sphere): -1.75
- CYL (Cylinder): -0.50
- AXIS: 175
- ADD: +1.00
This prescription shows:
- Both eyes are short-sighted (negative SPH values)
- There’s mild astigmatism in both eyes (CYL values)
- A reading addition of +1.00 for both eyes
Understanding this format allows you to quickly interpret the key components of your prescription for each eye.
The Importance of Understanding Your Prescription
Knowing how to interpret your eye prescription is beneficial for several reasons:
- Informed Decisions: You can make better choices about your eyewear, understanding which lenses might suit you best.
- Online Purchases: If you choose to buy glasses online, you’ll need to input your prescription correctly.
- Monitoring Changes: By understanding your prescription, you can track changes in your vision over time.
- Emergency Situations: In case you lose or damage your glasses while travelling, knowing your prescription can help you get a replacement quickly.
Beyond the Numbers: What Your Prescription Means for Your Eye Health
At Blue Fin Vision® Eye Clinic, we believe that your prescription is more than just a set of numbers. It’s a snapshot of your eye health and visual needs. Here’s what your prescription might indicate about your overall eye health:
Short-sightedness (Myopia)
If your SPH values are negative, you’re short-sighted. This means you can see nearby objects clearly, but distant objects appear blurry. Myopia is increasingly common, and can be corrected with glasses, contact lenses, or in some cases, refractive surgery.
Long-sightedness (Hyperopia)
Positive SPH values indicate long-sightedness. You might find it easier to see distant objects, but struggle with close-up tasks like reading. As we age, some degree of hyperopia is normal, but significant hyperopia at any age may require correction.
Astigmatism
If you have values in the CYL and AXIS fields, you have some degree of astigmatism. This common condition results from an irregularly shaped cornea or lens, causing blurred or distorted vision at all distances.
Presbyopia
The presence of an ADD value suggests presbyopia, a natural age-related change in near vision. It typically begins to affect people in their 40s and 50s, necessitating reading glasses or multifocal lenses.
Caring for Your Eyes Beyond the Prescription
While your prescription is crucial for clear vision, at Blue Fin Vision® Eye Clinic, we emphasise comprehensive eye care. Regular eye examinations can detect not only changes in your vision but also early signs of eye diseases and even some systemic health conditions.
The Importance of Regular Check-ups
We recommend annual eye examinations for most adults, even if you feel your vision hasn’t changed. These check-ups allow us to:
- Monitor changes in your prescription
- Screen for eye diseases like glaucoma and macular degeneration
- Assess your overall eye health
- Provide personalised advice on eye care and protection
Conclusion: Your Vision, Our Priority
Understanding your eye prescription is an important step in taking control of your eye health. At Blue Fin Vision® Eye Clinic in London, we’re committed to providing not just top-quality eye care, but also the knowledge you need to make informed decisions about your vision.
Whether you’re due for an eye examination, have questions about your prescription, or are considering new eyewear options, our team of expert optometrists and ophthalmologists is here to help. We combine cutting-edge technology with personalised care to ensure that your vision needs are met with precision and compassion.
Remember, your eyes are unique, and so is your prescription. By understanding what those numbers mean, you’re better equipped to care for your vision and overall eye health. Trust Blue Fin Vision® to be your partner in maintaining clear, comfortable vision for years to come.
