Understanding Contact Lens Numbers: A Comprehensive Guide

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.