You have gone to the optometrist, had your eye exam, and now it’s time to get your prescription. When you look at it, though, you’re perplexed, what do all these letters and numbers mean? How do they tell you what kind of glasses you should get?

Sample Eyeglass Prescription

Which numbers are my right eye and which are my left eye on my prescription?

In a typical prescription, two acronyms, one for each eye, are listed: 

O.D. (Oculus Dexter): This is short for oculus dexter, and is your right eye

O.S. (Oculus Sinister): This is short for oculus sinister, and is your left eye

OU. (Oculus Uterque): Used when a measurement or instruction applies equally to both eyes.

SPH is a common acronym for the sphere column. This is the lens power required to correct your eyesight. Nearsightedness is indicated by a minus sign (−) next to the number; you see better up close and require distance correction. You are farsighted if you have a plus sign (₊), which means your near vision needs to be corrected because you see better at a distance.

Since lens power is expressed in diopters, the sphere field above may be written as −9.00 D, indicating nine diopters of nearsightedness. Consider the measurement system as an integer number line with zero in the center that doesn't require adjustment.

The stronger the prescription lenses needed, the higher the number. This may have an impact on the frames you choose because a higher prescription necessitates a larger lens curve.

Your cylinder number indicates your level of astigmatism, if any. This occurs when a portion of the cornea curves differently. An eye is typically shaped like a basketball; the curve remains constant as it is turned in any direction. Astigmatism causes an eye to be oval or egg-shaped, or more like a football from North America, with one curve being longer than the other. This distinct second curve is corrected by the CYL number. Your eyes are not quite round if the number is low, like 0.25, and they are quite oval if the number is high, like 3.00.

The Axis number in your prescription guides your optician on how to align the cylindrical power in your lenses, which is needed if you have astigmatism.

This number shows the angle of correction, measured in degrees from 1 to 180. An axis of 90 stands for a vertical alignment, while 180 indicates a horizontal one. A larger axis number does not mean your eyesight is worse; it only explains the direction in which the astigmatism is positioned.

Eyeglass and contact lens prescriptions are not the same, and there’s a simple reason why. Glasses sit a short distance away from your eyes, while contact lenses rest directly on them. Because of this, contact lens prescriptions include extra details like the exact size and specific brand that works best for you. 

Before you can order contacts, an eye care professional also needs to do a contact lens fitting to make sure they feel comfortable and suit your eyes properly. When buying, always make sure you’re using the right type of prescription. Keep in mind, prescriptions are valid for up to two years, and by law, you have the right to get a copy after every eye checkup.

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