After visiting an eye doctor to correct your vision, you will receive a piece of paper indicating your contact lens prescription. This prescription consists of technical acronyms that describe your particular needs in regards to corrective lenses. The formula for a contact lens prescription describes the kind of lens needed to produce the right amount of refractive error your lenses need to help you see normally. Once you understand the terms and abbreviations, you will be able to read your contact lens prescription without a problem.

Understand the main terms.

Each contact lens prescription lists the necessary strength for each eye. On your prescription, you may see the term oculus dexter or the abbreviation OD. OD is a Latin term for the right eye. The term oculus sinister, or OS, means left eye. If both of your eyes require the same prescription, you will see the term oculus uterque, or OU, meaning that the prescription is for both eyes.

• Most terms on contact lens prescriptions are measured in diopters, a unit of refractive power that is equal to the reciprocal of the focal length in meters of a lens. Diopter is often abbreviated as D.

Locate the term power (PWR) or sphere (SPH).

These numbers are usually the first set of numbers listed next to the OD and OS rows or columns. They indicate the strength of correction needed for that particular eye or, if OU is listed, both eyes.

• For example, if the field under OD reads -3.50 D, this indicates that you have 3.5 diopters of nearsightedness in your right eye. If the field under OD reads +2.00, this indicates that you have 2.00 diopters of farsightedness in the right eye.
• It is common for the correction to differ between the right and left eyes. If you find the term PL, which stands for Plano, it means the number is 0 and no correction is needed for that particular eye.

Understand the base curve (BC).

This term describes how the curvature on the inside of the lens should be. This is measured so the lens fits perfectly against your eye and fits the shape of your cornea. Unlike most of the other numbers, this number is measured in millimeters.

• This number typically ranges from 8 to 10. The lower the number in this column or row, the steeper the curvature of the lens will be.

Find the diameter (DIA). The diameter is the measurement of a straight line through the center of the contact lens. It lets the maker of your contact lenses know how big around you need your contacts to be to fit your eye. Like the BC, the DIA is also measured in millimeters.

• This is a very important measurement. If it is off, your lenses can cause irritation or abrasions on your eyes.

Decipher a lens equation.

Sometimes, your contact lens prescription can also be written in a simple equation form. The equation usually follows this order: +/- Sphere/Power +/- Cylinder x Axis, Base Curve' BC'= diameter DIA = number. For example: +2.25-1.50x110, BC=8.8 DIA=14.0.

• If you are unsure exactly how to read your lens equation, ask your doctor to translate it for you.