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. So what do the numbers and letters on your eyeglass prescription stand for? What does all the information mean? We break it all down for you below.
Please note: this information pertains to eyeglass prescriptions only. Contact lens prescriptions are not the same as eyeglass prescriptions because different information is required for each, and your prescription is calibrated based on the distance the device is from your eye. While contact lenses sit right on the eyeball, eyeglasses sit further out, which calls for an adjustment of the correction needed.
Nearsightedness vs. Farsightedness
Nearsightedness, also called myopia, can occur if the cornea is curved too much or if the eyeball is too long. Nearsighted individuals have difficulty seeing far-away objects but can see close-up objects clearly. Picture it like this: A child who is nearsighted is able to read a book well but has difficulty reading the chalkboard. Nearsighted prescriptions are signified with a minus sign and they increase at intervals (diopters) of 0.25.
Farsightedness, also called presbyopia, is indicated by the ability to 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 before the numbers and will increase in 0.25 increments.
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. Learn more about buying reading glasses.
How to Read Your Eyeglass Prescription
Understanding your glasses prescription comes down to knowing what the letters and numbers stand for. Please note, this information is for eyeglass prescriptions, not contact lens prescriptions.
Right Eye (O.D.) and Left Eye (O.S.)
These abbreviations come from the Latin words oculus dexter (O.D.) and oculus sinister (O.S.), which mean right eye and left eye respectively. Some prescriptions will just refer to your eyes as “right” and “left”. If you see O.U. listed on your prescription, that stands for oculus uterque, meaning “both eyes.”
This tells you whether you are nearsighted or farsighted and how much correction your eyes need. (If you’re unsure if you’re nearsighted, jump to the next section to read more. If the numbers listed for sphere are negative, you are nearsighted.) A plus sign or no symbol before the number 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 is a number listed in this column, you likely have astigmatism. The “cylinder” might be written with a plus or minus, but either way, it’s indicative of the degree of correction needed for your astigmatism.
You might also see this written as “X”. This number between 0 and 180 represents the orientation of the astigmatism. The horizontal median of the eye is indicated by 180 and the vertical median by 90. If you have astigmatism, your prescription will list an axis number.
Any number listed in the add column indicates the additional power in the reading (lower) section of a multifocal or progressive lens. Because this power corrects presbyopia, the number will always be positive.
PRISM (p.d.) and Base
A prism correction helps those who have double vision, a condition called diplopia. This condition occurs when light enters the eyes and instead of hitting the same place in each eye’s retina, the light hits a different part of the retina in each eye. This misalignment causes two images to be seen.
This unit of prism correction is measured in prism diopters, also noted as “p.d.,” and bends the light as it travels through the lens so the light hits both retinas in the same place. A prism correction will also require a direction of the prism to be noted on the prescription, which is found under the “base” section, and will either say “up,” “down,” “in,” or “out,” depending on the direction the light needs to be refracted. Learn more about prism correction here.
Your eye doctor should provide you with your eyeglass prescription after your exam, but you can call and request your prescription free of charge at any time. In fact, this law is protected by the Federal Trade Commission by the Prescription Release Rule.
Types of Eyeglass Prescriptions
The following descriptions refer to prescription eyeglasses, not over-the-counter reading glasses sold on Readers.com®.
Single vision prescription lenses can correct nearsightedness, farsightedness, and astigmatisms. They contain the same amount of vision correction throughout the entire lens.
At Readers.com®, the most common frame for single visions reading glasses is a full frame, which is worn like regular glasses. 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.
Prescription bifocals (sometimes called “lined bifocals”) typically contain two corrective powers 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.
A bifocal’s visible line does take some time to get used to, as your eyes have to adjust to moving from one portion of the lens to the other to see clearly.
At Readers.com™, we carry non-prescription bifocal style reading glasses.
Trifocals (sometimes called “lined trifocals”) contain three prescriptions within one lens. The top prescription 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.
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.
If you are in need of non-prescription reading glasses, a valid prescription is not required to purchase them. However, visiting your eye doctor annually for an eye health exam and vision screening is recommended, and your eye doctor can also give you guidance on the right reading power for you.
Blue Light Glasses
The lenses of blue light glasses are designed to help combat temporary eye strain caused by digital screens including but not limited to: computers, tablets, smartphones, and televisions. Many computer glasses have tinted lenses or blue light blocking properties to block out potentially harmful blue light.* Blue light glasses, also known as computer glasses, help with an intermediate viewing distance of around 20 to 26 inches, which is the distance most people sit from their computer screen. Learn more about the benefits of computer readers, or head directly to shop blue light glasses.
*Disclaimer: Lenses do not block all blue light. Lenses help reduce the amount of potentially harmful blue light transmitted through the lens and varies between lens types. Harmful blue light refers to the 415-455 nanometer range of the visible light spectrum.
The information provided on this blog is for informational and general educational purposes. Before making decisions regarding your eye health, consult with a health professional who can base their recommendations on an assessment that will provide for your individual needs. Read our full disclaimer here.