Understanding your contact lens prescription

Having a valid contact lens prescription is important for anyone interested in buying and wearing contact lenses to ensure that the contact lenses you purchase meet your vision’s needs. This prescription is determined and made available to you by your optician or optometrist once you complete an eye exam.

How do I read my prescription?

The prescription you receive from your practitioner after an eye exam states the specifications that your lens must have so that your vision is corrected. When you order your contact lenses, you can find this prescription on the contact lens box. You also have different prescriptions for each eye.

Normally, a written prescription has the following specifications: base curve, diameter, and power (or sphere). If you suffer from astigmatism, your prescription will also have Cylinder and Axis figures. It will also have figures for Addition and Dominant if you suffer from presbyopia.

Sample Prescription Specifications

Base Curve

Diameter

Power/Sphere

Cylinder

Axis

Addition

Dominant

Left

8.4

14.0

-0.50

-1.25

10

+1.0

N

Right

8.4

14.0

-1.25

-1.25

10

+1.0

D

Name and Validity

Your prescription will also include the specific type and brand of contact lenses (i.e. Acuvue Oasys) recommended for you by your optician or optometrist. It is important to remember that your prescription for your glasses will not be the same as your contact lens prescription. Also included will be the validity of the prescription, which begins on the day of your check-up and normally expires after one year.

Below is an example of an individual’s prescription as shown on the side of their 1-Day Acuvue Moist for Astigmatism box.

Prescription Info

What do the different prescription figures mean?

Standard Prescriptions

The figures below are found on all prescriptions. This includes prescriptions correcting myopia (nearsightedness), hyperopia (farsightedness), astigmatism, and presbyopia.

Base Curve (BC): It identifies the right fit of the lens in terms of curvature, indicating in millimeters the radius of the back of the lens. While some brands use non-numerical notations, most use 8.x or 9.x values.

Diameter (DIA): Measured in millimeters and is displayed as a value between 13.x and 15.x, the diameter of a lens identifies its width. It is most commonly found as a 14.x number.

Power (PWR/SPH): Also known as ‘sphere’ or ‘strength, the power of a contact lens is measured in dioptres and is found in negative (-) and positive (+) values). Negative values correct nearsighted vision, while positive values correct farsighted vision. A high number means that the eye needs stronger vision correction.

Prescriptions for Astigmatism

The figures below are found on prescriptions for correcting astigmatism.

Cylinder (CYL): Much like power, it identifies the additional vision correction needed for those suffering from astigmatism as well as the severity of the condition.

Axis (AX): It indicates the central angle at which vision would be corrected. This ameliorates the effect of the distorted curvature associated with astigmatism.

Prescriptions for Presbyopia

The figures below are found on prescriptions for correcting age-related presbyopia.

Addition (ADD): It indicates the level of correcting needed for seeing clearly and sharply at a close distance.

Dominant: Each eye’s prescription is marked with “D” for Dominant or “N” for Non-dominant to indicate which eye is more dominant than the other.