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Know Your Eyes: A Guide to Reading Your Contact Prescription

Young woman receiving contact prescription

You know it's time to get a new contact prescription. But you're not quite sure about when and where you'll get it. Once you actually have the prescription, how do you even read it? Is it supposed to be some secret language known only to those in the medical field? After all, the multitude of numbers and abbreviations can be pretty confusing.

Luckily, it doesn't have to be too hard to understand. That secret language? You can learn it and speak it too! Intrigued? Keep on reading to find out more!

We are going to tell you in simple terms:

Where to Get a Contact Prescription

In order to get a contact lens prescription, you have to visit an optometrist and complete an eye examination. This comprehensive eye exam helps the doctor determine if contacts are appropriate for you. You will also know what size and type of contacts are best for your eyes.

Usually, this type of exam is not going to take a substantial amount of time. But it can give you a lot of information about your eyes. Your prescription may offer daily, weekly, or monthly contacts.

Now that you have your contact lens prescription, you need to know what it's actually telling you about your eyes. After all, it can be difficult to get the doctor to explain the code if it's a busy day. Luckily, it's not terribly difficult to learn how to read your own prescription!

What Does the Information on the Paper Mean?

Young woman wondering about her contact prescription

The first thing to know is that your glasses prescription is not the same as your contact lens prescription. Make sure that you are looking at the right one as you read this quick guide. Otherwise, you won't be able to figure out what your contact prescription is really saying!

The paper that the optometrist gives you should have some basic information on it relating to you. You should be able to see the following information:

Obviously, the main part of the paper you are trying to understand is all those numbers though, right?

Unlocking the Code

Oculus Dexter

On the prescription paper, this is often shortened to read O.D. This simply means the right eye. Whatever the number that follows this abbreviation will apply to your right eye only.

Oculus Sinister

As you may have guessed, this is often shortened as O.S. This stands for the left eye. The number following O.S. is going to refer only to your left eye.

Oculus Uterque

If you happen to see this shortened as O.U. on your prescription, it refers to both eyes. This means that both your left eye and right eye have the same prescription. Since they are the same, they don't need separate sections.

Power or Sphere

Typically, you will find these numbers right beside the O.D., O.S., or O.U. abbreviations. If O.U. is on your form, the power (or sphere) numbers are going to be the same as well. If you have O.D. and O.S., the numbers will be different for the power/sphere for each eye.

These numbers tell you how strong or weak the prescription is going to be for your eyes. Negative numbers relate to myopia (nearsightedness). Positive numbers relate to hyperopia (farsightedness).

For example, if it says -1.75 D under O.D., this means you have 1.75 diopters of nearsightedness in your right eye. If you're curious, a diopter is a measure used by optometrists. The diopter is the refractive power of the lenses that is the same as the reciprocal of the focal length in meters.

You may have one eye that has a power correction and one that doesn't. The eye with no correction is referred to as Plano and will reflect as a 0 for that eye. This is totally normal, so don't worry if that is what is on your prescription!

Base Curve

This number tells you the curvature of each lens for each eye. The base curve, (or B.C.) dictates how closely the curvature of your lens will be to your eye's natural curve. It also indicates how the contact is going to fit into your eye and around your cornea.

Unlike most of the other numbers, the base curve is measured in millimeters. It will usually be somewhere between 8 and 10. If you have a lower number, that means that your cornea is more curved or bulged.


Does anyone remember what diameter means from geometry class? The diameter (or DIA), is the length of an imaginary line running through the middle of each contact lens. It tells you the required width of each of your lenses. Everyone's eyes are not going to have the same diameter, because each person's eyes are unique.

The diameter is one of the most vital measurements. Getting the diameters wrong means ill-fitting contacts. Poorly fitted lenses can lead to abrasions on your corneas. If left untreated, these corneal abrasions can lead to permanent vision loss. So make sure that the diameter for each eye is right when you order your contacts!

Brand Name

Young man pondering questions

Your optometrist will tell you, through the prescription, which brand of contacts is going to work for you. You don't want to stray from this recommendation, because this is the brand that best fits all of your needs.

Having the wrong prescription means wearing contacts that are not right for your eyes. This can not only lead to discomfort, but it can also give you some serious headaches!

Wearing contacts with a prescription that is either too strong or too weak can give you headaches from the extra strain on your eyes. When you try to see in spite of the non-perfect eyesight, your eyes strain to bring things into focus. Wearing the wrong contacts will make this worse. These adverse symptoms will last for as long as you wear these wrong lenses.

If the lenses are not the right fit, they may actually damage your eye health over time. There are specific reasons that your optometrist will prescribe a certain size or strength for you. Not abiding by those numbers can cause some real problems for your eyesight.

If you try to read your contact prescription using our tips, and you still have questions, then consult your optometrist. If your prescription is written in a different way, don't be afraid to reach out to your doctor for clarification.

Buy Some New Contacts!

Now that you understand your contact prescription, it's time to buy some new contacts! Be ready to rock your contacts with comfort and great eyesight.

If you are all set to get some contacts, go ahead and browse the vast selection of quality lenses available. But if you have specific questions, feel free to contact us so that we can help you.

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