What Do Contact Lens Numbers Mean?

Many people who wear contact lenses do not fully understand them. Whether they are for improving eyesight or for changing eye color, all contacts require a prescription. Wearing ill-fitted or poorly prescribed contact lenses can cause permanent tissue damage to the eyes.

Function

• A contact lens prescription is usually assigned by an optometrist or an ophthalmologist. After your vision is checked by an eye doctor, he will write a prescription using medical measurements and terms. This prescription determines the size and power of the lenses.

Significance

• The numbers that appear on the side of contact lens boxes, next to symbols, are measurements that determine the size of the lenses.

What are symbols?

• Some symbols used in lens prescriptions are OD, which stands for Right Eye; OS, which stands for Left Eye; OU, which stands for Both Eyes; BC, which stands for Base Curve; and Dia, which is short for Diameter.

Types

• There are different types of lenses. If you were prescribed toric lenses then there would be two additional columns: cylinder and axis. Toric lenses are prescribed for people with astigmatism.

Fun Fact

• A contact lens prescription is different from your eyeglass prescription. This is because contact lenses sit on the surface of the eye, while eyeglasses are 12 mm away from the eye.