Eyeglass Prescription Glossary / Abbreviations
Oculus Dexter (OD): Latin for right eye.
Oculus Sinister (OS): Latin for left eye.
Oculus Uterque (OU): Latin for both eyes.
Sphere or Power (SPH or PWR): This is the main strength of your eyeglass prescription, and is written in 0.25 increments. If the field has 'SPH', 'PL', 'PLANO', or '00', this means your there is a 0.00 power as should be entered as so. DiscountGlasses.com can create lenses for prescriptions with sphere ranges between -20.00 and +20.00.
Plano (PL): This indicates there is no spherical correction in this eye. A plano lens would have no focusing power or correction to it.
Balance: This indicates there is no vision correction in this eye. It's a non-prescription lens and is used when only one of your eyes requires vision correction.
Cylinder (CYL): This indicates the amount of astigmatism, and is written in 0.25 increments. Not all prescriptions have a cylinder correction, and some prescriptions have a cylinder correction in only one eye. If you don't have an astigmatism correction then your doctor may leave this field blank, or they may put 'SPH', 'DS', 'Plano', or '00' in this field. This means you do not have an astigmatism correction in one or both eyes. DiscountGlasses.com can create lenses for prescriptions with cylinder ranges between -5.00 and +5.00. Positive (+) cylinder values will be converted into negative (-). See our FAQ page for more information.
Axis (AX or X): This is also part of the astigmatism correction, and is written in increments of 1 (one). If there is no cylinder, then there should be no axis. Since it's a degree/angle, it will be represented as a value between 1 and 180. If there is no cylinder, it's possible that the doctor might enter 0, but this would just indicate that there is no axis. DiscountGlasses.com can create lenses for prescriptions with ADD ranges between +0.25 and +3.00.
ADD: This is a value that is commonly used for bifocal or progressive lenses, as well as reading glasses. It indicates how much power gets added to the distance Rx to create the reading-only Rx; or as it applies to the glasses you'll order from DiscountGlasses.com, it determines the correction strength for the bottom half of your bifocals progressive lenses. It is written in increments of 0.25. DiscountGlasses.com can create lenses for prescriptions with ADD ranges between +0.25 and +3.00.
Prism or Base or Base Curve: A prism is used when both eyes are not properly aligned and they need a prism to re-align them. The base is the rotation of the prism. These fields are rarely used, and the correction type is not currently offered on DiscountGlasses.com eyeglasses. There are two separate parts to a prism correction. The first part is the diopter strength (e.g. 2.0) and the second is the direction (e.g. BU). There are four different directions. Base-Up (BU), Base-Down (BD), Base-In (BI), and Base-Out (BO).
Pupillary Distance (PD): This is the distance between the centers of the pupils of your eyes. Learn more about how to measure your own PD in our Measuring Pupillary Distance (PD) page.
Segment Height or Seg Height (SH): This is the vertical measurement in millimeters from the bottom of the lens to the beginning of the progressive addition on a progressive lens, or the top line of a lined bifocal. Segment height does not apply to single vision lenses. You will need the frame to be able to measure segment height because you can only measure it while the glasses are on your head. For more information, visit our segment height page.
Near Vision or Near Vision Only (NV or NVO): This is written when your doctor is recommending reading-only glasses. This is also known as farsightedness.
Distance Vision or Distance Vision Only (DV or DVO): This is written when your doctor is recommending distance-only glasses. This is also known as nearsightedness.
Astigmatism: An optical condition that can cause blurry vision. This is corrected by a cylinder and axis correction on a prescription.
Binocular: A term used to describe the simultaneous use of both eyes at the same time.
Monocular: Refers to only one eye.
Progressive Additive Lens (PAL): The ADD value specifically for progressive lenses.
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