The eyeglass prescription is the combination of three numbers or letters that indicate the strength of your vision. If you wear glasses and have never had a professional eye exam, chances are good that your prescription consists of two numbers separated by a slash, such as -3.5/-2.0 or +1.00/+3.00 (also abbreviated as OD/OS). In this case, left-eye (-) means "minus" and right-eye (+) means "plus." The first number indicates how strong your lenses need to be for distant objects (usually out past arm's length), while the second number indicates how strong they need to be for near objects (from about arm's length up).

Interpreting the prescription

A prescription is a formula used to determine the best corrective lenses for your eyes. It's written on an eye chart, which is designed to test your eyes' refractive error (ability to focus light). The chart will feature rows of numbers and letters that become increasingly blurry as they move downward. You'll be asked to read these lines in order from top down, starting with the smallest line at the very top (which should be clear).

The way optical prescriptions work is by taking into account what type of refractive error you have and adjusting accordingly—so if you're farsighted, we'll prescribe glasses that help focus light on the retina; if you're nearsighted, we'll prescribe glasses that move light away from the retina.

The first column represents your right eye; second column represents left eye

OD and OS

OD and OS are the abbreviations for right eye and left eye. If a prescription is written with these numbers, then you have an OD prescription in one eye (right) and an OS prescription in the other eye (left). These numbers are often written as R and L, but they can also be written as OD (Right) or OS (Left).

In some cases, your doctor may write a single number that represents both eyes together. This would be called an OPD or ODS number. The first letter indicates which eye you are looking through—O is for right eye, P is for left—and the next two digits indicate how strong your lenses need to be corrected for nearsightedness (hyperopia), farsightedness (astigmatism), or astigmatism only.

Sph (sphere)

The Sph (sphere) column is the distance from the center of the lens to the center of the eye. It's usually written as a fraction or a decimal, like +0.50, -0/10, or -7.00/-9.00. This is typically the first term in your eyeglasses prescription because it helps us calculate other values that are needed to put together your nerd glasses prescription.

Cyl (cylinder)

The cyl is the correction for astigmatism. Cylinder is a number followed by a C, e.g., -3C.


The axis refers to the angle of your eyeglasses lens. The measurement is in degrees, and it can be rotated to adjust the lens.

This is important because not all axes are created equal; some are more suitable for certain prescriptions than others. A common example is astigmatism, which needs a different axis than non-astigmatism lenses do (the doctor will let you know which one).

The prescription for eyeglasses is like an algebraic formula, but it's not difficult to figure out once you understand the symbols.

The prescription for eyeglasses is written in a specific format. The first number is the sphere power, which describes how thick your lenses are at the center of your lens. If you have strong prescriptions, you may need to choose glasses with a sphere power of no more than -10, or else they may look too thick and block out light from your peripheral vision.


This article is meant to help you understand the basics of eyeglass prescriptions so that you can order glasses online or visit an optician with confidence. The prescription for eyeglasses is like an algebraic formula, but it's not difficult to figure out once you understand the symbols. Once you have your own pair of glasses, we hope that they will help make life easier and more enjoyable by improving your vision.

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