Have you ever tried to shift your focus from your eyeglasses to eyeglass prescription? Sometimes when you walk out of an eye exam, it feels like you need a prescription to read your prescription.Your eye doctor provides you with a sheet filled with acronyms and numbers that seem like a different language. Knowing how to read an eyeglass prescription has become essential! While you likely know whether you’re nearsighted, farsighted or have astigmatism, determining that from your prescription slip is another thing entirely.

Eye prescriptions can be hard to decipher, though. In order to be interpreted worldwide, eyeglass prescriptions are written in a standardized format with common notations. A glasses prescription is intended for the purchase of glasses only - it does not include information that is required in a contact lens prescription. If you wear contacts, you’ll need a prescription specifically for contacts

What do all these letters and numbers mean?

The numbers on your eyeglass prescription describe precisely how your glasses lenses should be cut. Keep your prescription up to date so these numbers can accurately reflect your visual needs. You’ll see several abbreviations and words labeling all of the important data on your prescription. Find more below to learn the meaning of SPH, CYL Axis, Prism, PD, and more.

Sphere:

The sphere (SPH) on your prescription indicates the lens power you need to see clearly. A minus (-) symbol next to this number means you’re nearsighted, and a plus (+) symbol means the prescription is meant to correct farsightedness.

Cylinder:

The cylinder (CYL) number indicates the lens power needed to correct astigmatism. If this column is blank, it means you don’t have an astigmatism.

Axis:

An axis number will also be included if you have an astigmatism. This number shows the angle of the lens that shouldn’t feature a cylinder power to correct your astigmatism.

Prism:

This is the amount of prismatic power, measured in prism diopters ("p.d." or a triangle when written freehand), prescribed to compensate for eye alignment problems. Only a small percentage of eyeglass prescriptions include a prism measurement.

If the numbers are marked with a plus sign (+) or no sign, you’re farsighted. If the numbers are marked with a minus sign (-), you’re nearsighted.

If your prescription reads -1.00, that means your eyeglasses need 1 diopter of strength to correct nearsightedness.

If your prescription reads +2.50, your eyeglasses need 2.5 diopters of strength to correct farsightedness. The higher the number, the more correction your vision needs.

A glossary of eye prescription abbreviations

• ADD stands for the additional lens power needed to make it easier for you to read. This number is seen on prescriptions for reading glasses or the lower portion of bifocal or progressive lenses.
• Axis is a number between 1 and 180. It indicates exactly where the astigmatism appears on your eye.
• BO, BI, BU, BD stand for base out, base in, base up, and base down. These abbreviations tell the eyeglass manufacturer exactly where to position the prism on eyeglasses that correct double vision.
• CYL stands for cylinder, or the amount of astigmatism in your eye. The cylinder and axis together help correct astigmatism.
• DV is an abbreviation for distance vision. This number indicates whether you have nearsightedness or farsightedness.
• NV stands for near vision, or the amount of power that needs to be added to make reading easier.
• OD means oculus dexter, or your right eye.
• OU stands for oculus uterque, or both eyes.
• OS is oculus sinister, or your left eye.
• PD means pupillary distance. Monocular PD is the distance from your pupil to the middle of your nose. Binocular PD is the distance from one of your pupils to the other pupil.

How do I read glasses prescription?

Some of the numbers in your prescription tell the eyeglass manufacturer how much correction your vision needs. Eyeglass strength is measured in diopters.

If you see a – , it indicates nearsightedness. If you see a +, it indicated farsightedness. If you notice an ‘Add’ power, it means you require magnifying lenses, such as progressives.

When you’re buying glasses, all you need to do is make sure the numbers on your prescription match the numbers in the prescription field on your screen.

In the sample below, the right eye is prescribed -2.50 sphere to correct nearsighted vision. This eye needs a cylinder of -0.75 and an axis of 173 to correct astigmatism, and an ADD power of +2.25 to correct near vision. The ADD value is usually present in a multifocal prescription.

The left eye is prescribed with a sphere of -3.00 to correct nearsighted. This eye needs a cylinder of -1.00 and 004 to correct astigmatism, and an ADD power of +2.25 to correct near vision. Without the ADD value, it is a single vision prescription.

How often should you get an eye exam?

If you don’t have any medical issues that affect your vision, you should have a comprehensive eye exam every one to two years.