How to Read Your Glasses Prescription: A Simple Guide to SPH, CYL, AXIS & More

If you have ever taken a look at your glasses prescription and wondered what all those numbers and abbreviations mean, this post is for you!

There are terms like "SPH", "CYL", "VA", "ADD" and more. A prescription can seem like just a string of numbers that only an optician or optometrist can understand. But each part actually tells us something specific about your vision and the type and amount of correction your eyes require.

Here's a simple guide to better understand your prescription.

1. SPH - Sphere

SPH stands for Sphere. This is usually the first number you'll see, and it indicates the main power needed to correct your vision.

Sphere power corrects myopia (short-sightedness) or hyperopia (long-sightedness).

What does a minus (−) sign mean?
A minus prescription generally indicates myopia. For example: SPH −2.00 means the lens requires −2.00 diopters of spherical power.

What does a plus (+) sign mean?
A plus prescription generally indicates hyperopia. For example: SPH +1.50 means the lens requires +1.50 diopters of spherical power.

What do the numbers mean?
The further the number is from zero, the greater the spherical correction.

What does plano mean?
If you see PL, Plano or 0.00 on a prescription, this means no spherical power is required. 

2. CYL - Cylinder

CYL stands for Cylinder. This refers to the amount of correction that is required for astigmatism.

Unlike a spherical prescription, which has the same power in every direction, an astigmatic eye has different focusing powers in different directions. A cylinder correction is used to compensate for this difference.

For example: CYL −1.00 indicates −1.00 diopters of cylinder correction.

You might see either a plus or minus cylinder notation, depending on how the prescription is written. In Singapore, minus-cylinder notation is commonly used, so you will often see prescriptions written like: SPH −2.00 / CYL −0.75 / AXIS 180.

Don't be concerned if you see a different format on an older prescription or one from another country. A qualified optician can transpose the prescription between plus- and minus-cylinder formats when appropriate.

And if your CYL is blank or recorded as 0.00, it generally means no astigmatic correction has been prescribed.

3. AXIS - The direction of astigmatism

If you have a cylinder prescription, you'll usually see an axis value next to it. The axis describes the orientation of the astigmatism correction.

It is measured from 1° to 180°.

Take for example: CYL −1.00 × AXIS 180

How to interpret this:
−1.00 = how much cylinder correction is required
180 = the orientation of that correction

A useful way to remember it:

• CYL = how much
• AXIS = which direction

The axis number itself does not indicate the severity of your astigmatism. A prescription with an axis of 10 isn't necessarily "less" or "more" astigmatic than one with an axis of 170.

4. ADD - Additional near power

ADD stands for Addition. You'll most commonly see this on prescriptions for bifocal or progressive lenses.

As we get older, our eyes gradually become less able to focus on objects up close. This is known as presbyopia or colloquially as "lao hua yan" in Singapore. It usually affects people around age 40 & above. 

An ADD value indicates the additional power needed for near vision, on top of the distance prescription.

For example: ADD +1.50 means an additional +1.50 diopters is required for near vision.

Importantly, an ADD of +1.50 doesn't mean that your distance prescription is +1.50. It's additional near power.

Do note that addition can also be found on digital lenses, which are specialty anti-fatigue lenses for students and young adults who have long hours on screentime or near work everyday. For digital lenses, the ADD values are usually lower than that of progressive or bifocal lenses.

5. PRISM - Helping the eyes work together

Some prescriptions include PRISM.

Prism correction is used when the eyes need help with alignment and coordination.

You may see a prism amount together with a direction, such as:

• Base Up (BU)
• Base Down (BD)
• Base In (BI)
• Base Out (BO)

Not everyone needs prism correction. If you don't see a prism value on your prescription, that's perfectly normal. 

6. VA - Visual Acuity

VA stands for Visual Acuity. Unlike SPH, CYL and AXIS, VA isn't a lens power. Instead, it describes how clearly you can see.

You may see measurements such as:

• 6/6
• 6/9
• 6/12

Or, in some countries, the equivalent:

• 20/20
• 20/30
• 20/40

The numbers represent your ability to see detail at a specified testing distance. In Singapore, VA is commonly recorded using the metric notation, so you'll often see values such as 6/6, 6/9 or 6/12. In countries that use feet instead of metres, the equivalent notation is 20/20, 20/30 and 20/40.

The first number refers to the testing distance, while the second indicates the distance at which a person with standard vision can see the same line.

6/6 means you can see at 6 metres what a person with standard vision can see at 6 metres.

What’s the difference between unaided and aided VA?

Unaided VA is how clearly you can see without glasses or contact lenses. Aided VA is how clearly you can see with your vision correction.

Take for example: Unaided VA: 6/18 → Aided VA: 6/6

This means your vision improves from 6/18 without correction to 6/6 with your glasses or contact lenses.

Here are some other commonly asked questions we get at our practice!

Q: Why Are My Right and Left Eye Prescriptions Different?

It's completely normal for your two eyes to have different prescriptions.

Your right eye might be −2.00, while your left eye might be −1.50. Or one eye might have astigmatism while the other doesn't. 

If there is a significant difference in refractive power between both eyes, it is known as anisometropia. 

Your optician considers both eyes individually when determining the appropriate lens correction.

Q: Are My Spectacle and Contact Lens Powers the Same?

Not necessarily. Your spectacle and contact lens prescriptions may differ, especially for higher prescriptions.

Spectacle lenses sit slightly away from your eyes, while contact lenses sit directly on the surface of your eyes. This difference in distance can affect the power needed for clear vision.

Always get your contact lens power properly assessed and fitted by an eye care professional.

Q: Can My Prescription Have a CYL But No SPH?
Yes. You can have astigmatism correction without spherical power.

Q: What is the Difference Between My Distance and Reading Prescription?
Your reading prescription includes the ADD on top of your distance prescription. For progressive lenses, both are incorporated into one lens.

Your Prescription Is Only the Starting Point

Once you know your prescription, there's another question: What kind of lenses should you put it in?

Two people with exactly the same prescription may not necessarily benefit from the same lenses.

Various factors such as:

• your prescription strength
• your age
• how much time you spend on screens
• your working distance
• driving habits
• reading habits
• frame size and shape
• how the frame sits on your face
• lens material and index
  
• lens design
  
• coatings

can all influence which lens is appropriate for an individual.

This is particularly important for progressive and other personalised lens designs, where measurements and how you use your glasses can make a meaningful difference to your experience.

The Bottom Line

Your prescription may look complicated, but the basic idea is fairly simple:

SPH → your main lens power
CYL → amount of astigmatism correction
AXIS → direction of astigmatism
ADD → additional near power
PRISM → helps with eye alignment issues
VA → how clearly you can see

And if you're still staring at your prescription thinking "…okay, but what does mine actually mean?" - that's what your optician is there to help you understand.

At Raylite Optical, we believe choosing eyewear shouldn't just be about knowing your numbers. It's about understanding what those numbers mean for the way you see.

Visit Us:

Raylite Optical Tampines
Address: 201-D Tampines Street 21 #01-1133
Singapore 524201
Nearest MRT: Tampines East MRT (DTL)

🔍 Why Visit Us in Tampines?

• Serving since 1985 – trusted by generations of families
• Thousands of frames across over 30 brands
• New arrivals and best-sellers every season
• Certified ZEISS Vision Expert & Essilor Expert
• Advanced eye care instruments for better diagnosis

📍 We’re located at Tampines N2 Shopping Street, just a 5-min walk from Tampines East MRT (Downtown Line)!