The abbreviations OD and OS that may be included with corrective eyewear prescriptions stand for “oculus dexter” and “oculus sinister.” In other words, this is Latin for “right eye” and “left eye,” respectively.

If you need vision correction following an eye exam, your ophthalmologist or optometrist will let you know if you’re nearsighted or farsighted. They may even tell you that you have an astigmatism.

With any diagnosis, you’ll be given a prescription for corrective eyewear. Your prescription will have a number of abbreviated terms such as:

  • OD
  • OS
  • SPH
  • CYL

Do you know what these mean? We explain.

Step one of understanding the prescription from your eye doctor is knowing OD and OS. These are simply abbreviations for Latin terms:

  • OD is an abbreviation for “oculus dexter” which is Latin for “right eye.”
  • OS is an abbreviation for “oculus sinister” which is Latin for “left eye.”

Your prescription might also have a column for OU, which is an abbreviation for “oculus uterque,” Latin for “both eyes.”

Although OS and OD are traditional abbreviations used in prescriptions for eyeglasses, contact lenses, and eye medicines, there are some doctors who have modernized their prescription forms by replacing OD with RE (right eye) and OS with LE (left eye).

Other abbreviations you might notice on your eyeglass prescription include SPH, CYL, Axis, Add, and Prism.


SPH is an abbreviation of “sphere” which indicates the power of the lens your doctor is prescribing to correct your vision.

If you’re nearsighted (myopia), the number will have a minus sign (-). If you’re farsighted (hyperopia), the number will have a plus sign (+).


CYL is an abbreviation of “cylinder” which indicates the lens power your doctor is prescribing to correct your astigmatism. If there’s no number in this column, then your doctor hasn’t found an astigmatism or your astigmatism does not need to be corrected.


Axis is a number from 1 to 180. If your doctor has included cylinder power, there will also be an axis value to indicate positioning. Axis is measured in degrees and refers to where the astigmatism is located on the cornea.


Add is used in multifocal lenses to indicate the additional magnifying power for the bottom part of the lens.


Prism only appears on a low number of prescriptions. It’s used when your doctor feels that compensation for eye alignment is necessary.

When looking at your eyeglass prescription, you might see specific lens recommendations that your doctor has included. These are typically optional and may incur additional charges:

  • Photochromic lenses.Also referred to as variable tint lenses and light-adaptive lenses, this makes the lenses automatically darken when exposed to sunlight.
  • Anti-reflective coating.Also called AR coating or anti-glare coating, this coating reduces reflections so more light passes through the lenses.
  • Progressive lenses.These are multifocal lenses with no lines.

While your eyeglass prescription has all the information necessary for you to buy eyeglasses, it doesn’t have information necessary for purchasing contact lenses.

This information includes:

  • lens diameter
  • curve of the back surface of the contact lens
  • lens manufacturer and brand name

Your doctor will also sometimes adjust the amount of corrective power between glasses and contact lenses based on the distance the lens will be from the eye. Glasses are about 12 millimeters (mm) away from the surface of the eye while contact lenses are directly on the surface of the eye.

Depending on your specific situation — currently using corrective eyewear, age, risk factors, and more — most eye doctors suggest having a comprehensive eye examination every year or two.

At that time, if necessary, your doctor will provide a prescription for you to use when purchasing eyewear. This prescription can appear confusing until you know the meaning of abbreviations such as OS, OD, and CYL.

Remember that the prescription you get for eyeglasses isn’t a prescription for contact lenses as well. You can’t get a prescription for contact lenses until your doctor has performed a fitting and evaluated your eyes’ response to contact lens wear.