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How do i Read my Glasses Rx

Learning to understand your eyeglasses prescription is tricky but necessary. This friendly guide simplifies the process.

An updated eyeglasses prescription is the first step to being able to buy stylish and affordable glasses online. Unfortunately, so few understand what is written on that piece of paper that it makes filling out the order form really difficult and often results in mistakes that end up causing errors in the manufacture of your new eyeglasses.

Learning what all those signs and symbols mean is crucial to you being in control of your visual health.

So let’s get started with a very brief explanation of what the abbreviations on your prescription really mean:

OD is oculus dextrous which means your right eye
OS is oculus sinister which means your left eye
SPH is sphere – the main part of your prescription. It states the strength of your prescription in diopter.
CYL is cylinder – indicating the strength of your astigmatism (if you have one).
AXIS is the rotation of the cylindrical lens (CYL) that runs on a plane of 1-180 degrees.
PL is plano – which means there is no vision correction needed (basically you want frames fitted with clear glass lenses for fashion purposes).
D.V. means distance vision
N.V. means near vision – sometimes it says NVO
ADD is short for additional value
PD is the distance between your pupils or pupil distance
OU just means both eyes
PAL means progressive additive lens and it is the additional value for your progressive lenses.
Balance means that one eye has a prescription and the other eye has no useful vision.
X is short for Axis.
Prism happens when both eyes are not properly aligned and they need a prism to re-align them.
Base is the rotation of the prism. The prescription will read:
BO – base out
BI – base in
BU – base up
BD – base down

Every doctor writes their prescription differently so one really needs to take note of the abbreviations and work out the meaning accordingly.

Note: the numerical values will always be written with either plus (+) or a minus (-) sign in the SPH as well as the CYL and ADD. These signs are probably the most crucial of the whole prescription as mixing them up will determine how and whether at all you can see.

As noted above, SPHERE (SPH) is the strength of your prescription in 0.25 increments. Nearsighted (problems seeing in the distance) people will usually have a minus (-) sign in their sphere while farsighted (problems seeing up close) people will have a plus (+) in their prescriptions.

Your optometrist or eye doctor may have also written your SPH or CYL as +150, which is equal to +1.50.

For those with an ASTIGMATISM, you will have a note on your prescription for your CYLINDER (CYL). Basically, this is when your eye is curved and that curvature makes your vision blurry unless corrected. Some people may only have astigmatism in one eye and many people don’t have one at all, in which case, that field will be left blank. Alternatively, they will write SPH, 00, Plano, or DS – all meaning that you do not have astigmatism.

If you do have a CYL, then you will also have an AXIS, which tells you at what degree that CYL lens must be manufactured. Axis should be from 1-180 degrees and will always be a whole number. If your Axis is written as “6”, it can be entered as 06 or 006.

The ADDITIONAL VALUE (ADD) is most commonly used for multifocal glasses as well as for single vision reading glasses. You need to look carefully for these numbers as your doctor may write them in the near vision (N.V.) or ADD sections, or merely indicating on the side that this is the ADD. There are times when your doctor will only write the ADD once, meaning it is for both eyes, while other times (and more correctly), each eye will be given its own value. Single vision distance glasses do not require an ADD reading and this can just be left off your order form, although this is recommended for better vision. Those needed special glasses like reading, progressive or bifocal glasses, MUST include this information to avoid manufacturing blunders.

Your pupil distance (PD) is not often written on your prescription and so, you should always check before leaving your doctor’s office. The average PD is 62mm and most people fall within the 54mm to 74mm range. Measuring your own PD is tricky, and should be done by a professional. It is never wise to guess this otherwise the optical center of the glasses will not align with your pupils, will give you headaches and will not feel comfortable.

Your PD can be written a few different ways, ie: 63; 32/32; 33/31; 30.5/33.5; 63/60.
If your PD is written as 63 – simply insert it as 63. If your PD is written as 32/32, you can add the two together and insert 64 or you can write each number separately. If your PD is written as 33/31 or 30.5/33.5 – the measurements from the center of your nose to the pupil on either eye is not equal and you should insert your PD as written on your prescription. Do not add the numbers together.

Remember, with all this said and done, the most reputable online eyeglasses companies will also allow you to email or fax your prescription to them so that they can double check that all is correct OR so that they can simply fill it in for you.