Deciphering your eyeglass prescription can be confusing, especially if you’re getting glasses for the first time. Going to your eye exam armed with knowledge on how to read your script and about the types of prescriptions can help you make a smarter decision when it comes time to pick out your glasses. Here’s what you need to know:
How to Read an Eye Prescription
Understanding your glasses prescription comes down to knowing what the letters and numbers stand for.
O.D. and O.S.
O.D. represents your right eye and O.S. represents your left eye. Some prescriptions will just refer to your eyes as “right” and “left”.
This tells you whether you are nearsighted or farsighted and how much correction your eyes need. If the numbers are negative, you are nearsighted. A plus sign means you are farsighted and could be in need of reading glasses. Usually, the worse your eyesight is, the further from zero the number will be.
If there are three numbers in your prescription, you probably have astigmatism. The “cylinder” might be written with a plus or minus, but either way, it’s indicative of the degree of your astigmatism.
You might also see this written as “X”. This whole number between 0 and 180 represents the orientation of your astigmatism, not a power.
If this is present on your prescription, it means you need correction for presbyopia. The number indicates the magnifying power added to the lowest (reading) portion of a progressive lens.
Not all prescriptions have a prismatic power, as this power is used to correct issues with eye alignment.
Nearsightedness vs. Farsightedness
Nearsightedness can occur if the cornea is curved too much or if the eyeball is too long. Nearsighted individuals have difficulty seeing far-away objects. Picture it like this: Someone who is nearsighted is able to read a book well but has difficulty reading street signs. Nearsighted prescriptions are signified with a minus sign and they increase at intervals (diopters) of 0.25.
People who are farsighted can see far-away objects with no problem, while close-up objects are blurry. Farsightedness occurs when light that enters the eye focuses behind the retina instead of on it. A prescription for farsightedness always has a plus sign.
Many farsighted individuals only wear glasses while reading or doing something up close. For this reason, reading glasses offer a practical solution for people who spend a lot of time concentrating on close-up material. Those over the age of 40 likely have developed presbyopia, and need reading glasses to correct their farsightedness.
Types of Eyeglass Prescriptions
Single vision prescription lenses can correct nearsightedness, farsightedness, and astigmatisms. They contain the same amount of vision correction throughout the entire lens. In terms of single vision reading glasses, full frame readers are the most common. You’ll also find single vision lenses in half frame reading glasses, which are narrower and sit at the end of your nose for easier up-close and distance viewing.
Bifocals (sometimes called “lined bifocals”) contain two prescriptions within the same lens and can correct both nearsightedness and farsightedness. Usually, bifocals contain focal lengths that correct close vision of 12 to 18 inches from the face and distances of 10 feet and beyond. When you’re looking at someone who is wearing bifocals, you can see the line between their nearsighted and farsighted prescription.
Trifocals (sometimes called “lined trifocals”) contain three prescriptions within one lens. The top Rx corrects distance vision, the middle corrects intermediate distances (18 to 24 inches), and the bottom corrects up-close vision. Just like with bifocals, you can visibly see the lines between the prescriptions on the lens.
Progressives are multifocal lenses that contain at least three prescriptions. Similar to trifocals, progressive lenses have three main fields of vision, including near, intermediate, and distance. However, progressives do not have a visible line between prescriptions. This gives the wearer a seamless and uninterrupted transition when looking from up-close objects to far-away distance.
*These types of eyeglass prescriptions are not referring to any lens types on Readers.com.
The lenses of computer glasses are designed to deal with eyestrain caused by computer screens. Computer glasses help with an intermediate distance of around 20 to 26 inches, which is the distance most people sit from their monitor. Many computer glasses have tinted lenses to filter out potentially harmful blue light radiating from your electronic devices. For more information on the benefits of computer readers, click here or head directly to purchase a pair here.
Even if you don’t have an eyeglass prescription from your eye doctor, you may find yourself needing reading glasses. A valid prescription is not required to purchase over-the-counter reading glasses, though your eye doctor can tell you the magnification you need. For more on buying readers, click here.
Note: Glasses prescriptions are not the same as contact lens prescriptions and cannot be used interchangeably.