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 opportunities are becoming more and more popular, and there are many interesting deals to purchase a wide variety of glasses online: from sunglasses to prescription glasses and blue light glasses.  

Understanding how our eye prescription works will open up a lot of new opportunities to explore different types of glasses without needing the advice of an optician. (Check our fit guide to learn which frames would suit you best!).

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

Glasses prescriptions explained

Glasses prescriptions explained

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?


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 we know that a prescription is made up of numbers and signs, here’s how to read them with some examples:
-1.00: would relate to one diopter of nearsightedness.
-4.25: would relate to four and ¼ diopters of nearsightedness.
+1.00: would relate to one diopter of farsightedness.

How to read a prescription for astigmatism?

How to read a prescription for astigmatism?

Astigmatism is often caused by a cornea that is shaped like a football instead of perfectly round. That’s why, when it comes to reading a prescription for astigmatism, more elements have to be taken into account. As such, astigmatism is based on these three elements:

S x C x Axis (for example: -2.50 -0.75 x173).

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

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

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

Other additional elements to take into account:

Other additional elements to take into account:

ADD: to correct presbyopia (age-related farsightedness). The ADD indicates if you’d need bifocal or progressive lenses, which would correct the vision at the same time as helping to focus for far or near distances, depending on the case. As such, it would allow adding two different prescriptions in one, for far and for near distances.

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 here.

An example of astigmatism prescription explained

An example of astigmatism prescription explained

Let’s imagine you’ve been given these numbers: -2.00 +1.50 x180, what does that mean?

In this case, the numbers on the left are indicating that a person has 2 diopters of nearsightedness with 1.5 diopters of astigmatism and an axis of 180 degrees.

How to find out what prescription your glasses are

The best and most reliable way to find out what prescription your glasses are is to ask an optician to read the power of your glasses with a lensometer. Additionally, an optician or optometrist will also be able to update your prescription after an eye examination.
Keep in mind that prescriptions tends to change over time!

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

Our lenses range

Our lenses range


Range of lenses: We can suit any 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. 

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