How to Read Your Rx

Contact Lens Rx Abbreviations

Don’t be intimidated by the abbreviations and numbers on your contact lens Rx. It’s not secret code. Although arriving at the numerical measurements on your prescription requires precision equipment and a thorough eye exam by an eye care practitioner, the measurements on your contact lens prescription are relatively easy to understand with a general knowledge of geometry and the concept of magnification. 

OD – Oculus Dexter: Latin term for “Right Eye”

OS – Oculus Sinister: Latin term for “Left Eye”

OU – Oculus Uterque: Latin term for “Both Eyes”

DS – Doptris Sphere: your lenses have “sphere” power only.

PD – Pupillary Distance: the distance in millimeters between your left pupil and right pupil.

SPH – Sphere Power: the overall power of the lens

PWR – Refractive Power: the measurement or amount of diopters a contact lens must provide to sharpen distance vision to an acceptable level (as close to 20/20 vision as possible). A minus signs means the prescription is for the correction of nearsightedness (myopia) and a plus sign means the prescription is for the correction of farsightedness (hyperopia). The farther from zero these numbers, the greater amount of correction the contact lenses call for.

BC – Base Curve: the back curve of a contact lens measured in millimeters. For maximum comfort, fit and eye health, a contact lens is curved to match the curvature of your cornea—the lower the number, the steeper the curve of the cornea (the clear outside layer of your eye).

DIA – The diameter of your contact lens as measured in millimeters from one edge of your contact lens to the opposite edge.  This measurement determines where on the eye the contact lens rests. If the diameter is off, abrasion, irritation and discomfort can result.

CYL – Cylinder: this measurement correlates to the correction of astigmatism and in diopters measures the extent of astigmatism.  A minus sign refers to correcting a myopic astigmatism (nearsighted) and a plus sign refers to correcting a hyperopic astigmatism (farsighted).

AXIS – Axis: a measurement for contact lenses designed to correct astigmatism. A contact lens Axis is measured in degrees and refers to the orientation of the contact lens on the eye and the degree to which it compensates for the oval shape of an astigmatic cornea.

PL / plo – PLANO: this means lenses are plain and have no corrective qualities whatsoever.

NV/NVO – Near Vision or Near Vision Only: your eye doctor recommends reading glasses.

DV – Distance Vision: for the correction of farsightedness  (hyperopia).

ADD – Add Power: typically found in bifocal contact lens prescriptions for reading or other close-up viewing. ADD is measured in diopters and is assumed to be a positive (+) measurement even if not indicated on your contact lens Rx.

COLOR – This applies only to colored contact lenses or otherwise cosmetic contacts or theatrical contact lenses. If contacts are colored, the name of the color (blue) will appear here. If contacts are theatrical in nature, i.e. “Zebra” the style or name of contact lenses will appear here.

BRAND – This denotes the manufacturer or brand of contact lens, i.e. PureVision, Air Optix and indicates to retailers that the prescription applies only to the brand stated on your contact lens Rx.

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Why a prescription for contacts?

A contact lens is an FDA approved medical device that requires an eye exam and prescription in the United States. A contact lens prescription is good for up to a year in most U.S. states and must be obtained from a licensed ophthalmologist or optometrist. Some states, however, allow opticians certified in contact lens fitting to issue a contact lens Rx.

Is my eyeglass prescription and contact lens prescription the same thing?

Although a prescription for eyeglasses and a contact lens Rx may contain similar information, a contact lens prescription is more in depth and contains measurements for lenses that sit directly on the eye’s cornea as compared with eyeglasses that don’t.

If my prescription expires can I still get contacts?

No. You must have a valid contact lens prescription to obtain contact lenses from licensed eye care professionals on Although you may think nothing about your eyes or vision has changed since your last eye exam, it’s imperative that you get re-examined for proper fitting and corrective contact lens powers.

General Contact Lens Rx Information

 If you don't see numbers in some of the boxes on your prescription (for example no CYL or AXIS or ADD), then they don’t pertain to your corrective needs. If you only see one number for each eye, it's normally the "SPHERE" power, and other fields may not apply. It’s also common for contact lens fitters to leave out the decimal points, so numbers like -50 or +175, are understood to mean -0.50 or +1.75, respectively. Also, an axis of 5 (or 05) is the same as 005 and 90 is the same as 090.

Your doctor may use a blank Rx pad, not a pre-printed Rx pad for your contact lens prescription. If this is the case, make sure all abbreviations and numbers are legible so that if you order from a source other than your eye care professional, they can fill your contact lens prescription properly.

If you have NO astigmatism in one or both eyes, your doctor may just write the sphere power alone, or may use placeholders like SPH ("sphere") or D.S. ("dioptres sphere") instead.

If your contact lenses are strictly for cosmetic purposes and not corrective action, you still need an eye exam and contact lens Rx to obtain contact lenses from a eye care professional or otherwise reputable source for contact lenses.

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Who is authorized to prescribe contact lenses?

Ophthalmologists are licensed physicians and surgeons and have an extensive level of education - typically twelve to fifteen years of undergraduate work, medical school and advanced training. They can perform ophthalmologic examinations, prescribe vision correction (glasses or contact lenses) medications and diagnose and treat diseases and disorders of the eye. In addition, ophthalmologists can diagnose general diseases of the body and treat ocular manifestations of systemic diseases.

Optometrists are licensed healthcare providers who have completed four years of undergraduate work and four years of optometry school. They can perform eye exams, prescribe and dispense eyeglasses and contact lenses and diagnose vision disorders and eye diseases. Optometrists can prescribe medications to treat certain eye diseases.

Opticians are technicians who have graduated from a two-year program at a community or technical college. They are qualified to make, fit, and dispense eyeglasses and contact lenses, either in an optical laboratory or for retail sale to the public. Opticians are not licensed to perform patient examinations in the U.S., but in some states are allowed to fit contact lenses.

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Contact Lens Myths

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Eye Exams are Important

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How to read your contact lens Rx

  • Contact lens Rx abbreviations
  • Why a prescription for contacts?
  • General contact Rx information
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