OD is short for the Latin term oculus dexter which means right eye.

OS is an abbreviation of the Latin oculus sinister which means left eye.

You’ll often see this terms on eyeglass prescriptions.

Sphere: The sphere (SPH) on your prescription indicates the lens power you need to see clearly. A minus (-) symbol next to this number means you’re nearsighted, and a plus (+) symbol means the prescription is meant to correct farsightedness.

Cylinder: The cylinder (CYL) number indicates the lens power needed to correct astigmatism. If this column is blank, it means you don’t have an astigmatism.

Axis: An axis number will also be included if you have an astigmatism. This number shows the angle of the lens that shouldn’t feature a cylinder power to correct your astigmatism.

This is the most common format with clearly printed fields for OD, OS, SPH, CYL, etc.; values are usually entered with computer, but may be handwritten by doctor.

Rx Notes:
Sphere (SPH) and Cylinder (CYL) always have a (+) or (-) sign. On any prescription, PD can be written in different ways: e.g., 62 (Single PD), 33/31 (Dual PD), or 62/60 (Distance PD/Near PD).

The information on this free-form prescription is usually handwritten.

For multi-focal glasses, as well as reading and computer glasses, your Rx will include an ADD or NV value. This number always has a (+) sign.

Rx Note: The type of Rx glasses may be noted on a prescription, such as DV [Distance Vision/nearsightedness] and NV [Near Vision/reading].

The less common prism Rx refers to the amount of prismatic power needed to compensate for eye alignment issues (e.g., double vision or “lazy eye”). The prism Rx will have two values: PRISM & BASE.

Rx Note: BO=Base Out, BI=Base In, BU=Base Up, and BD (or BDn)=Base Down.

Unlike typical Rx formats, with values going from left to right, the vertical Rx values are listed top to bottom. This format is less common in the US.

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