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How to Read Your Prescription? [Complete Guide]

If you’re trying to remember which contact is which, or just want to understand what your prescription means, we’ve got you covered.

If your vision, while reading, seems fuzzy or you are unable to see long distances, visiting an optometrist is your first step

The optometrist will test your eyes and determine if you need glasses. And if you do need glasses or contacts, they’ll write you a prescription

But, most people do not know how to read prescriptions for glasses. In this article, we show you exactly how to read your prescription for glasses.

When you might need glasses or contacts?

If you don’t already have glasses or contacts, it’s important to understand the signs and symptoms that indicate you may need corrective eyewear.

If you already have your prescription, feel free to skip this section.

1. Blurred vision

A common reason to have eyes tested is due to blurred vision. Blurred vision is often a gradual process that you may not immediately notice it.

What can be a clear sign is if others on the street always recognize you before you recognize them. But also, if you can no longer see the individual leaves on the trees or if you cannot read the letters on a traffic sign properly.

Blurred vision and reading difficulties are signs that you may need corrective lenses

2. Reading difficulties

Usually, people with a minus power often have difficulty reading the subtitles on the television, and people with a plus power often have to hold the newspaper or a book further away in order to read the letters. Also, people who don’t see well often have trouble reading in a dimly lit place.

Did you know that if you have difficulty reading – from far or near, it can also lead to incorrect posture? You bend too much towards the screen and get problems with your back and neck or you may have to sit all the way back to be able to read a text.

3. Headache

Another common complaint is a headache. This is when you can’t see well and have to put in the extra effort. For example, do you have to squeeze your eyes to see more clearly? This can be the cause of headaches.

In addition to headaches, you may also have tired eyes. If you suffer from headaches and do not see well, wearing glasses or contact lenses can be the solution.

Do you experience one or more of the above symptoms? Then we recommend that you visit the optometrist.

During an eye test, the optician checks the health of your eyes. He or she will also examine whether you have any eye defects.

Each eye is checked separately, in addition to how your eyes work together. Based on the eye test, you will receive personal advice so that you can see comfortably and sharply.

Having Headaches? They may be related to your eyes if you also have blurry vision or trouble focusing

Prescription terms to know

On a standard prescription, you’ll see several abbreviations and terms followed by numbers. Each of these terms means something different.

But don’t worry, we’ve got you covered.

 Here is a quick overview of what they stand for:

(SPH ) SphereIndicates the power of the lenses needed
(CYL) CylinderIndicates the measure of Astigmatism
AXISThe measure of the angle of the eye meridians
PRISMIndication of diplopia and degree of correction needed
(ADD) AdditionalCorrection needed for presbyopia
(PD) Pupillary distanceDistance between centers of both pupils

We will explain these terms further, in more detail using the example prescription below:

Example Prescription


For most people, the above prescription may seem to be just a bunch of letters and numbers. But if you understand what it means, it can help you buy the right glasses online or offline with confidence.

What does OD and OS mean on a prescription?

On a prescription, each eye is denoted by the abbreviation OD and OS, otherwise known as R and L, respectively.

OD is the abbreviation for Oculus Dextra, which is the Latin term for the right eye.

OS is the abbreviation for Oculus Sinistra, the Latin term for the left eye.

You could also come across the abbreviation OU that stands for ‘Oculus Uterque’, which means ‘both eyes’ in Latin.

In some prescriptions, you may also find RE and LE which stand for Right eye and Left eye.

How do you read a prescription?

Reading a prescription from your optometrist can be tricky. There are lots of different eye disorders out there such as short-sightedness, farsightedness, near-sightedness, and so on.

These are all noted on your prescription, but they can be tough to understand.

We’ll explain these terms including SPH, CYL, AXIS, ADD, and PRISM better in the video and section below:

SPH or Sphere

SPH or Sphere notes the power of the lens needed by the eyes, which can be a plus or minus lens.

If the number entered in the column is a minus sign (-), it means you are nearsighted. 

If the number in the column is followed by a plus (+) sign or neither preceded by a plus or minus sign, it means you’re farsighted. 

To put it simply, the higher the number written (in addition to the minus sign or plus), the thicker the lens your eyes need.

CYL or Cylinder

CYL or Cylinder indicates whether you have astigmatism. If there are no numbers in this column, you do not have astigmatism or very little astigmatism which does not need lenses to correct them. 

If there is a number in this column followed by a minus sign (-), it means near-sightedness astigmatism. And if the number is followed by a plus (+) sign, it means far-sightedness astigmatism.


The Axis value indicates if your prescription includes cylindrical power. This represents the angle (in degrees) between the astigmatic eye’s two meridians. 

It is usually denoted by a number that ranges between 1-180. 90 denotes the vertical meridian and 180 denotes the horizontal meridian.

PRISM or Base or Base Curve

PRISM or Base Curve indicates the amount of correction needed in people who have double vision also known as diplopia.

The PRISM number is written as fractions or decimals and then the direction of the prism. This basically depicts the amount of misalignment of the eyes.

There are four abbreviations in the direction of the prisms, namely BU (base up = above), BD (base down = bottom), BI (base in = towards the user’s nose), and BO (base out= towards the user’s ear).

ADD (Additional)

If you have been diagnosed as having presbyopia you will also need magnifying power added to the bottom part of multi-focal lenses. This is found in the ADD section of your prescription, which stands for additional.

Presbyopia is the loss of near focusing ability which happens due to aging. People with presbyopia have difficulty seeing small text and fonts like you’d find on a cell phone.

This ADD value is represented by a number between +0.75 to +3.0 D.

Even if the plus sign is not written, it is to be taken as a plus power. And typically this value will be the same for both eyes.

Your eye doctor may use a Phoropter (pictures) to test your vision


PD is the abbreviation for pupillary distance, which is the distance (in millimeters) between the centers of each pupil. 

This is important to know if you want comfortable eyewear. For women, PD is usually around 56-62 mm and 58 mm+ for men (averaging around 64mm).

Other Useful Resources

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