How to Read Your Eyeglass Prescription

OD stands for "oculus dexter" (right eye) and OS for "oculus sinister" (left eye). Your prescription lists values for each eye separately. Some prescriptions also use OU (both eyes together) for values that apply to both.

The main correction strength, measured in diopters. A minus (−) sign means you are nearsighted (myopia). A plus (+) sign means you are farsighted (hyperopia). The further from zero, the stronger the correction. Common range: −0.25 to −8.00 for nearsightedness; +0.25 to +4.00 for farsightedness.

This value corrects astigmatism — an irregular curvature of the eye. Not everyone has astigmatism; if this field is blank or shows "DS" (diopters sphere), you do not have significant astigmatism. The cylinder value is always written alongside an AXIS value.

The axis describes the orientation of the astigmatism correction, measured in degrees from 1 to 180. It is meaningless without the CYL value — they must be used together. If your CYL is blank, your AXIS will also be blank.

If your prescription includes an ADD value, you need bifocal or progressive lenses — the ADD is extra magnification for reading, added to the bottom of the lens. Common for people over 40. ADD is always a positive number, typically between +0.75 and +3.00.

The PD is the distance in millimetres between the centres of your pupils. It is used to centre your lenses correctly in the frame. Your optician may give you a single number (monocular PD averaged for both eyes, e.g., 63mm) or two numbers for each eye separately (e.g., 31.5 R / 31.5 L). You need your PD when ordering prescription lenses — but you do not need it to order frames.