How to read eye prescriptions: become an expert!

How to read eye prescriptions: become an expert!

It is becoming increasingly important to learn how to read eye prescriptions. After all, e-commerce eyewear brands are becoming more and more popular, and there are many plenty of opportunities to purchase a wide variety of glasses online- from sunglasses to prescription glasses to blue light glasses.  

Understanding how your eye prescription works will open up a lot of new opportunities to explore different types of glasses without needing the advice of an optician.

Here’s a quick guide to help you become an expert at reading eye prescriptions!

Glasses prescriptions 101

Glasses prescriptions 101

Prescriptions for eyeglasses are typically represented by a series of numbers listed under different headings: OS and OD, or OU.  

What is the meaning of eye prescriptions?

These refer to Latin abbreviations:
- OS: oculus sinister, referring to the left eye
- OD: oculus dextrus, for the right eye
- OU: oculus uterque, both eyes.

Although these are still the most common terms for prescription glasses, some doctors have started to modernize their eyeglasses prescriptions with the use of RE, for the right eye and LE for the left one. 

NEARSIGHTEDNESS AND FARSIGHTEDNESS: HOW TO READ THE NUMBERS?

NEARSIGHTEDNESS AND FARSIGHTEDNESS: HOW TO READ THE NUMBERS?

Generally speaking, the further away a number is from 0, the more vision correction will be needed (a stronger prescription).

The measurement used is “sphere”, known as S or SPH, which refers to the spherical portion of the prescription measuring the degree of nearsightedness or farsightedness.

There are some elements to take into consideration:
+ refers to farsightedness
- refers to nearsightedness
D is the unit used to measure the correction. The numbers represent diopters.


So now that we know that an eye prescription is made up of numbers and signs, here are a few examples to practice breaking it down:
-1.00: this represents 1 diopter of nearsightedness.
-4.25: this represents 4 and ¼ diopters of nearsightedness.
+1.00: this represents 1 diopter of farsightedness.

Understanding your eye prescription

Understanding your eye prescription

These are the three elements that are important in an eye prescription:

S x C x Axis

(for example: O.D -2.50 -0.75 x173 / O.S -3.00 -1.00 x004).

- SPH or SPH: measures the degree of nearsightedness or farsightedness

- C or CYL: indicates the amount of lens power or degree of astigmatism, and it can be negative or positive. The bigger the number, the stronger the astigmatism

- Axis: a number between 0 and 180 degrees that reveals the orientation of the astigmatism, in order to know where the curvature is taking place

Astigmatism, the degree measured in CYL, is often caused by a cornea that is shaped like a football instead of being perfectly rounded. It also means that there are a few more things to take into consideration when reading your prescription.

Other additional elements to take into account

Other additional elements to take into account

ADD: represents the additional correction needed for presbyopia (age-related farsightedness). The ADD indicates if you’d need bifocal or progressive lenses, which corrects vision while helping put things in focus for either far or near distances, depending on the case. As such, it would allow adding two different prescriptions in one, for farsightedness and for nearsightedness.

At Barner, we are not currently producing progressive lenses, but we can offer blue light glasses with a single prescription: either to help you with nearsightedness, so you can better see distant objects, or with farsightedness, so you can read better. If you’d like to know more, click here.

PD (Pupillary distance): Refers to the distance, in millimeters, between both pupils in the eyes. It is typically used to center the graduation of the lenses. If you need help measuring your PD, check our FAQs below!

An example of astigmatism prescription explained

An example of astigmatism prescription explained

Let’s imagine you’ve been given these numbers: O.D -1.00 -0.50 x180, what does that mean?

In this case, the numbers are indicating that a person has 1 diopter of nearsightedness with -0.5 diopters of astigmatism and an axis of 180 degrees.

HOW TO FIND OUT WHAT PRESCRIPTION YOUR GLASSES ARE

HOW TO FIND OUT WHAT PRESCRIPTION YOUR GLASSES ARE

Already have a pair of glasses and curious about what your existing prescription is? Ask an optician or optometrist to read the power of your glasses with a lensometer as this will give you the most reliable reference point.


Keep in mind that prescriptions tends to change over time, so it’s always a good idea to renew your prescription every year or so to make sure it’s up to date!

How strong is my eye prescription?

How strong is my eye prescription?

According to the American Optometrist Association (AOA) [1], these are the following levels of prescription:

MILD

- Nearsightedness: -0.25 and -2.00
- Farsightedness: +0.25 and +2.00

MODERATE

- Nearsightedness: -2.25 and -5.00
- Farsightedness: +2.25 and +5.00

HIGH

- Nearsightedness: lower than -5.00
- Farsightedness: higher than +5.00

prescription how

Our prescription range

Our prescription range


Range of lenses: We can accomodate any eye prescription ranging in power from +6.00 to -8.00, and Cylinder (CYL) from +4.00 to -4.00. 

Please keep in mind that the sum of sphere and cylinder metrics can only reach a maximum of -8 or +6. 

To order your prescription lenses online, you can check this useful article

FAQS