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 cannot 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 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 so anyone can understand it.
Table of Contents
When might you need glasses or contacts?
If you don’t already have glasses or contacts, it’s essential 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.
What can be a clear sign is if others on the street always recognize you before you realize 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.
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 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 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 must put in extra effort. For example, do you have to squeeze your eyes to see more clearly? Again, this can be the cause of headaches.
In addition to headaches, you may also have tired eyes. If you often have 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. You will receive personal advice to see comfortably and sharply based on the eye test.
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 the terms on your eye prescription mean:
| (SPH ) Sphere | Indicates the power of the lenses needed |
| (CYL) Cylinder | Indicates the measure of Astigmatism |
| AXIS | The measurement of the angle of the eye meridians |
| PRISM | Indication of diplopia and degree of correction needed |
| (ADD) Additional | Correction needed for presbyopia |
| (PD) Pupillary distance | Distance between centers of both pupils |
We will explain these terms further, in more detail, using the example prescription below:
Example Prescription
| SPH | CYL | AXIS | ADD | PRISM | |
| OD | -1.50 | -0.75 | 90 | +2.00 | 1BU |
| OS | -2.25 | -1.25 | 180 | +2.00 | 1BD |
For most people, the above prescription may seem like just a bunch of letters and numbers. But if you understand what it means, it can help you confidently buy the right glasses online or offline.
What do 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, 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 which stands for ‘Oculus Uterque,’ which means ‘both eyes’ in Latin.
In some prescriptions, you may also find RE and LE, which stand for right and left eye.
How do you read a prescription?
Reading a prescription from your optometrist can be tricky. This is because there are many eye disorders, such as short-sightedness, farsightedness, and near-sightedness.
These are all noted on your prescription but 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 (-), you are nearsighted.
If the number in the column is followed by a plus (+) sign or neither preceded by a plus or minus sign, you’re farsighted.
Simply put, 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.
AXIS
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 represents the vertical meridian, and 180 indicates the horizontal meridian.
PRISM or Base or Base Curve
PRISM, or Base Curve, indicates the correction needed in people with double vision, also known as diplopia.
The PRISM number is written as fractions or decimals, and then the direction of the prism. This 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 with 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, as 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.
PD
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. PD is usually around 56-62 mm for women and 58 mm+ for men (averaging about 64mm).
Other Useful Resources
- Oakley Prescription Glasses and Sunglasses Guide
- How Much Do Prescription Sunglasses Cost?
- Does Your Prescription Get Worse Over Time?
Have a question?
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