You know glasses and contacts are used to correct vision problems, including nearsightedness (myopia), farsightedness (hyperopia), presbyopia (aging of the eye lens) and astigmatism (when the curvature of the cornea or natural lens are asymmetrical). 

This group of vision problems are called “refractive errors,” meaning the shape of your eye doesn’t bend light correctly and instead of seeing clearly, you see a blurred image. Your prescription, whether for glasses or contacts, is a recipe for everything needed to correct your specific refractive errors. 

What do the numbers, abbreviations, and symbols on my prescription mean? 


You might see abbreviations on your prescription, such as OD, OS, OU, SPH, CYL and ADD. Here’s what they mean:

OD, OS, and OU are Latin abbreviations and refer to the right eye, left eye, or both eyes respectively. 

OS is for oculus sinister, and means the left eye. OD stands for oculus dexter, and refers to the right eye. OU is for both eyes, and stands for oculus uterque. 

D — Diopters, the unit used to measure your vision correction (the refractive power of the corrective lens).

SPH — Sphere, or the amount of lens measured in diopters. 

CYL — Cylinder, indicating the amount of power you need to correct astigmatism (when your cornea has a more oblong shape vs. a round shape or a football shape vs a basketball shape). 

Axis — This tells you the orientation of the astigmatism, anywhere between 0 and 180 degrees and where the meridian is flatest vs the steepest meridian 90 degrees away. 

PD — Pupillary distance, or the distance between the centers of your pupils. 

Dist., Inter, or Near — These stand for distance, intermediate and near. 

BVD — Back vertex distance, or the distance from the back of your glasses lens to the apex of your cornea. 

ADD — Addition, used in bifocals and indicating additional correction needed for reading.

Numbers and Symbols

Numbers will be listed under the headings OD and OS, and refer to the diopters used which is a unit of measurement that represents and inverse relationship to the focal length of light for a particular dioptric power. The diopters will be listed in positive or negative terms, indicating nearsightedness (Myopia) and farsightedness (Hyperopia).  

A “minus” (-) sign indicates you are nearsighted, while a “plus” (+) indicates you are farsighted. 

For example, -1.25 indicates that you have one-and-a-quarter diopters of nearsightedness. A prescription that says +3.00 means you have 3 diopters of farsightedness. 

The further from zero the number is on the prescription, the worse your eyesight and the stronger your prescription. 

Are glasses prescriptions and contact lens prescriptions the same? 

The two are different. While a contact lens prescription includes the lens power needed to correct your refractive error, it also contains additional information that your eye doctor gains from a contact lens exam and fitting. 

  • Base curve (BC) — This is the measurement of the curvature of the back surface of the contact lens, and is determined by the shape of your cornea. 
  • Diameter (DIA) — This indicates the size of the lens, and along with the base curve, the diameter determines how your contact lens will fit. 
  • Contact lens material or brand — This is important because different lens materials have different degrees of oxygen permeability and lens design. 

How often will my prescription change? 

Dr. Chad Carlsson, founder of Carlsson Family Eye Center, recommends getting an eye exam every year. Most spectacle prescriptions and contact lens prescriptions are good for one year in most States except for maybe one or two States where a prescription may be good for 2 years. 

Vision prescriptions aside, your eye doctor will be able to screen you for diseases of the eye (such as macular degeneration, glaucoma and much, much more) during a routine eye health exam, and, just as important, your eyes are a window into your overall health. 

Do you need an updated prescription for glasses or contacts? Come in and see us! Make an appointment today.