How To Understand Your Contact Lens Prescription

Overview

Contact lenses are a prescription item used to correct vision problems. A contact lens prescription contains more information than an eyeglasses prescription, because the measurements of the eye are very important when fitting contact lenses. When you receive your prescription for contact lenses, you will see several different abbreviations and numbers. Knowing what these stand for will help you to understand your contact lens prescription.

Step 1

Look at the top of the prescription, and notice the abbreviations "OD" and "OS." According to All About Vision, OD stands for oculus dexter, which is Latin for right eye. OS stands for oculus sinister, which means left eye. Everything under the OD column will apply to your right eye, and everything under the OS column will apply to your left eye.

Step 2

Understand what the refractive power number means. The next line will be a positive or negative number. This is the power that the contact lens must be in order to bring your vision in the applicable eye to perfect vision, which is commonly referred to as 20/20 vision. All About Vision states that a negative number will indicate nearsightedness, and a positive number will indicate farsightedness.

Step 3

Note the measurements of the base curve, or BC, and the diameter, or DIA. According to the Eye Care Source, the base curve is the measurement of the natural curve of your cornea. The diameter is the measurement of the contact lens from one side to the other. Both of these must match your eye to avoid irritation and possible abrasions to your eye.

Step 4

Note whether you have an astigmatism, which the Mayo Clinic defines as an irregularity in the shape of your eye. The cylinder (CYL) indicates the amount of irregularity that you have, and the axis, measured in degrees, indicates where it is on your eye.

Step 5

Determine whether you need bifocal vision correction. If you do, it will be indicated by a number in the ADD row, according to All About Vision. A bifocal correction will help you to see for close-up work, such as reading.

Step 6

Note the color of your contact lenses as well as the brand specified in the last two rows. The color boxes will only be filled in if you have chosen to have contact lenses that will enhance or change your eye color. According to the Eye Care Source, the brand name must be specified on prescriptions given in the United States. In some cases, a specific brand may not be available, and may be substituted.