Glasses prescriptions can be confusing sometimes it may appear to be written in mysterious code but actually once you understand the meaning of the symbols, it will all make sense.
In the example below, we learn how to read the eyeglasses prescription, you will need to understand what the symbols mean first.
Right Eye and Left Eye Abbreviations
Since we’re nearly always looking at prescriptions for two eyes, you’ll nearly always see two sets of numbers, one for the left eye, and one for the right.
OD: Oculus Dextrus as means right eye in Latin.
OS : Oculus Sinister Latin terms for left eye.
OU: Your prescription may or may not contain this one. It stands for oculus uterque which means both eyes
Sphere (SPH) – This shows the strength of your glasses, or lens power, measured in diopters (D). A negative (-) sign indicates nearsightedness (in which case you have myopia) while a positive (+) sign or no sign at all indicates farsightedness (hyperopia).
Cylinder (CYL) – This shows the lens power for astigmatism, the condition of having an irregular lens shape caused by both nearsightedness and farsightedness. It is measured in plus and minus diopters as above. If the Cylinder field is empty, you have no astigmatism so there is no correction needed.
Axis – This is a number from 1 to 180 which describes the lens meridian that contains no cylinder power to correct astigmatism. If your eyeglass prescription has a Cylinder power, it must also have an Axis value (sometimes preceded by an x when written in freehand).
Add – This field contains any added magnifying power for people with presbyopia (or aging vision) and is featured in the bottom part of a multifocal lens. As a result, this is always a positive (+) number and is usually the same in both eyes.
Prism – This is for the uncommon occurrence of eye alignment problems. It is measured in Prism Diopters (p.d. or a superscript triangle if written freehand).
Base – This refers to the thickest edge of the Prism, which is also the direction towards which the Prism redirects light (up, down, in, or out)
PD: Pupilillary Distance (PD) or interpupillary distance (IPD) is the distance (the industry standard is to measure in millimeters) between the centers of the pupils in each eye. This measurement is used when preparing to make prescription eyeglasses
take a look at our PD measurement tips for more information.
An Example Of An Eyeglass Prescription
A good rule of thumb when reading a prescription is this: the further from zero each number is, the worse your eyesight.
In above example the optometrist has prescribe -2 D sphere for the correction of myopia in the right eye (OD). There is no astigmatism correction for this eye, so no cylinder power or axis is noted.
The left eye(OS is being prescribe -3 D sphere for myopia plus -0.5 D cylinder for the correction of astigmatism. The Cyl power has its axist at the 180 meridian, meaning the horizontal (180-degree) meridian of the eye has no added power for astigmatism and the vertical (90-degree) meridian gets the added -0.50 D.