Interpreting Your Contact Lens Prescription
Eye doctors use standard terms, abbreviations and measurements to write contact lens prescriptions. It can look like a secret code at first, but it's really quite simple to decipher.
Below is a sample contact lens prescription. Place your cursor over each element for explanation on the right.
understanding your lens prescription
- Patient:
- Prescribed by:
| Header 1 | Right Eye (OD) | Left Eye (OS) |
|---|---|---|
The anatomy of Contact Lens Prescription
Run your mouse over the prescription form to find out what all those numbers and abbreviations mean.
Please Note: This is not an actual contact lens prescription! As far as we know, no existing lens contains this combination of features and measurements.
If you have further questions about your prescription please contact your doctor.
Refractive power
The amount in diopters, of correction the lens must provide to sharpen your distance vision to an acceptable level (usually 20/20).
The minus sign means that this prescription is for nearsightedness (myopia). A plus sign means correction for far-sightedness (hyperopia). The farther from zero, the greater the amount.
The patient has mild to moderate near-sightedness and needs a different prescription for each eye, which is not unusual.
If you have further questions about your prescription please contact your doctor.
Base Curve
The back curvature of a contact lens is measured in millimeters. For best fit, comfort, and eye health, it is prescribed to match or complement the curvature of your cornea.
The lower the number, the steeper your cornea.
If you have further questions about your prescription please contact your doctor.
Diameter
The distance, in millimeters, from one edge of your contact lens to the opposite edge.
This measurement is important because it determines where on your eye the edges of the contact lens will rest. If the diameter is wrong, irritation or abrasion can result.
If you have further questions about your prescription please contact your doctor.
Cylinder
The cylinder is necessary if your lens is corrected for astigmatism. Measured in diopters, the cylinder shows the extent of your astigmatism.
The negative sign means myopic astigmatism. A plus sign means hyperopic astigmatism.
All contact lens prescriptions must have a cylinder in the negative format.
If you have further questions about your prescription please contact your doctor.
Axis
The axis is necessary in measuring for correction of astigmatism.
The axis is expressed in degrees. It indicates the orientation of the cylinder in the lens, in order to compensate for the cornea's oval, rather than round shape.
If you have further questions about your prescription please contact your doctor.
Add power
The add power is expressed in diopters. Even if the plus sign is not written on the prescription, it is assumed.
Bifocal contact lenses usually contain a prescription for reading or other close-up viewing. Some bifocal do not use numbers to express the add power, they will instead use "high" or "low".
If you have further questions about your prescription please contact your doctor.
Color
This is included only if the contact lens changes or enhances your eye color. Or, in the case of special effect contacts, a particular design is written here, such as "cat-eye".
Color and style names differ from one brand to another.
If you have further questions about your prescription please contact your doctor.
Brand
In the United States, contact lens prescriptions always indicate a specific brand.
The law states that contact lens retailers must sell you that brand and no other. However, in the case of some "private-label" contact lenses that are sold only by eyecare professionals, substitution of an equivalent national brand or private-label brand may be permissible.
If you have further questions about your prescription please contact your doctor.
In addition to the above information, your prescription may note how often your contact lenses must be replaced (once a month, every two weeks, once a week, daily, etc.). Or you may be instructed verbally, during your exam. Often the lens brand includes this information (e.g., Ophtha-Lens One-Week), but the real judge is your eyecare practitioner, who knows which replacement option is best for your eyes and lifestyle.