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When you choose to wear contacts lenses to treat vision problems, it's important that your contacts are the exact brand, size, and strength your doctor prescribes.^[1] However, deciphering the words and numbers on your contact lens prescription can be hard at first. Typically, a contact prescription contains a brand name, lens base curve, lens diameter, and lens power so you can easily order the right corrective lenses. Research suggests that it's important to double check that the contacts you receive are the same ones your doctor prescribed before you wear them.^[2]

[Edit]Steps

[Edit]Reading a Typical Lens Prescription

Locate your prescription. When your eye doctor gives you the paperwork from your visit, she will hand you your prescription. This comes in the form of a graph or table in your eye care paperwork. Although this is the standard form, the terms on the columns or axes of the graph varies according to your doctor's preference.
- Make sure you are looking at the contact lens prescription, not your eyeglasses prescription. This is to ensure you understand exactly what kind of lenses you are going to get. The two tables may include similar acronyms, but the numbers may differ.^[3]
Recognize the general information. The FDA requires that all contact lens prescriptions provide some basic information about the optometrist prescribing the lenses and the patient receiving them. They require the patient's name, the examination date, the issue date of the prescription, the expiration of the prescription, and the name, address, phone number, and fax number of the optometrist.
- The information about the lens strength must also be on the prescription as well as any special instructions or brand requirements.^[4]
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.^[5]
- 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.^[6]
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.^[7]
- 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.^[8]
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.^[9]
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.^[10]
Get the right brand. In the United States, your optometrists will always indicate the brands of contacts that will best fit your needs. Once they list those brands, it is the law that the retailer who provides your contacts must supply you one of those brands and no other.
- Substitutions can be made for natural brands as well as private label lenses, which are those only sold by eye care professionals.^[11]
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.

[Edit]Reading a More Involved Lens Prescription

Look for the term cylinder (CYL). There are certain numbers that do not always appear on your prescription. If you are suffering from astigmatism, which is common, you will see the added column or row for CYL. This number is the measure of the amount of astigmatism you have, measured in diopters. Most doctors use a positive number, but if a negative number is given, a lens store may need to convert to a positive number.
- This usually caused by an irregularly shaped cornea, but can also be caused by an irregularly shaped lens on the eye.
- A negative number here indicates your Myopia (nearsighted) astigmatism and a positive number means you have Hyperopia (farsighted) astigmatism.^[12]
- Keep in mind that US and Asian lens prescriptions use minus cylinder notation, while European lens prescriptions use plus cylinder notation.
Find your axis (AXIS) number. The axis is the measurement calculated in degrees that is required to bend light to correct the irregular shape of the cornea. This is essentially the orientation needed for your CYL to work properly.^[13]
- This number will be a higher number, such as 090 or 160, depending on how slanted your CYL needs to be.^[14]
Understand the term add power (ADD). Sometimes, it may be necessary for you to have contact lenses with bifocals in them. If this is the case, your prescription may have a column or row for ADD, which is the amount that the lens needs to be adjusted for the bifocal lenses.
- This term is measured in diopters.^[15]
Ask your optometrist about color (COLOR). There may be a reason your prescription includes the term color. This is a field that indicates if you requested a certain kind of contact lens to enhance to color of your eyes. This can also indicate a special kind of contact, such as "cat eye" or some other eye changing quality.
- The special features available will differ depending on the brand you need. Ask your optometrist about your options based on your current condition.^[16]