How to Read an Eyeglass Prescription
Your prescription looks like a spreadsheet full of abbreviations and decimals. Here is what each column actually means, in plain English, from independent lens consultants who read them every day.
OD vs OS: which eye is which?
OD is Latin oculus dexter — your right eye. OS is oculus sinister — your left eye. Some clinics write RE and LE. If you see OU, it means both eyes. The two rows on your prescription almost always list OD first, then OS.
SPH — sphere
The main lens power. A minus number corrects nearsightedness (myopia); a plus number corrects farsightedness (hyperopia). The bigger the number, the stronger the prescription. A "plano" or 0.00 means no spherical correction in that eye.
CYL — cylinder
The extra correction for astigmatism — an uneven curvature of the cornea. If CYL is blank or 0.00, you have no astigmatism in that eye. Otherwise it will show a small number with a sign, always paired with an Axis.
Axis
An angle between 1 and 180 degrees that tells the lab where to orient the cylinder power on the lens. Axis only exists when there is a CYL value. It is a direction, not a strength — Axis 180 is not "stronger" than Axis 90.
ADD — the reading boost
Additional plus power for near vision, used in bifocal and progressive lenses. It usually shows up from the early forties as presbyopia sets in. The same ADD value applies to both eyes on almost every prescription.
PD — pupillary distance
The distance between the centers of your pupils, in millimeters. The lab uses it to place the optical center of each lens directly in front of your pupil. A wrong PD is one of the most common reasons new glasses feel "off," especially in progressives.
Prism and Base
Prescribed less often — prism corrects how the two eyes align. If it appears, it comes with a base direction (up, down, in, or out) that tells the lab which way to bend light through the lens.
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