Your prescription is the most important element when you buy prescription glasses online - it's what enables us to custom-make each pair of glasses. However, we know it can be difficult to understand your prescription details, which is why we have written this Online Prescription Glasses Guide. Every doctor writes their prescription differently, therefore to help you understand your eyeglasses prescription, this section will take you through the various parts and explain what to look out for.

In case you're not comfortable with filling your glasses prescription out online, you can simply send us your prescription by fax or by e-mail and our optical experts will fill it out for you! In order to send us your prescription by fax or by e-mail, all you have to do is to click the "send your prescription by fax / e-mail" buttons in the "enter your prescription" section and to follow the simple instructions.

On a typical prescription, you will see two sets of rows. Most of the time the top portion is for your Right Eye or OD while the bottom portion is for your Left Eye or OS.

Prescriptions are generally laid out as follows:




- Please pay close attention to plus and minus signs as it will affect your lens.
- Eye doctors will often leave out the decimal point on the sphere, cylinder, and addition. For instance, -5 or +150 is understood as -0.50 and +1.50. Let's explain what all of these measurements mean.

SPH or SPHERE

Sphere indicates the strength of your prescription in 0.25 increments. For distance correction, there is usually a value under sphere (SPH) and it generally marked as negative (-). The abbreviation is “D.V.” or Distance Vision.

In this box you may also see the following signs:

This sign is quite common and looks like an 8 on its side but it stands for 'infinity'. Sometimes 'PL' is used instead. You should enter 00 or 'plano' for that part.

CYL or CYLINDER

This figure is required if you have something called an 'astigmatism'. It should be a number between +/-4, in 0.25 increments.
Doctors will often use positive (+) cylinder but some use negative (-), there is a BIG difference between the two so please pay close attention to the signs.
Not all prescriptions have Cylinder (CYL)/AXIS values. If you don't have astigmatism correction, doctors may leave it blank but they might also put SPH, 00, Plano, or DS which means sphere or Diopter Sphere. To fill your glasses prescription online you can enter either nothing (leave the column blank), or select the phrase none or 00 in the drop down.

AXIS

Please note that that Cylinder (CYL) and Axis are always provided together. For any value of Cylinder there should always be a value for Axis. Axis should be from 1-180 degrees. If you see a number like '6' under axis, it is also the same as '006' or '6 degrees.' It should always be a whole number and never with a decimal point on the axis. Please note: when inserting your axis into the field provided, only insert a number like 6 instead of 006.

ADD or Near Addition

The Add is mostly for people over 40 and concerns bifocal or progressive glasses for reading and near correction.

Sometimes opticians write the addition as a complete additional line on your prescription, sometimes once (same for both eyes) and sometimes once for each eye. Only one ADD means that the addition for both the left and right eyes are the same.

If you have a multi-focal prescription glasses but only want to purchase single-vision prescription lenses for distance correction, just leave off the ADD part which is for the bottom near or reading correction of the bifocal. If you are ordering reading glasses, please keep the ADD on the prescription.

PD

In order for our glasses to perform at their best, we need to create lenses that can match the distance between your eyes, so the center of each lens aligns with the center of your pupils. For this reason, we need your pupillary distance measurement – also known as the PD measurement.

Unfortunately, many opticians don't include your PD in the prescription. However, you can ask your optician for it directly during your eye exam. If you already have your prescription, we can make your prescription glasses using the average PD measurement. While it works well for most customers, it can cause discomfort or strain for others. If you have a strong prescription or your PD is significantly differently from the average, you may experience some problems with prescription glasses that have the average PD measurement.

Pupillary distance can be measured on your own with a tape measure. If you chose to measure your own PD, please do so in millimeters. Simply have someone measure from the middle of the left pupil through to the middle of the right pupil. Make sure you are looking straight forward at a distant object.

Average PD is about 62mm and most people fall within the 54 to 74 range. If your number is outside this range, you may have made a mistake. Please do not guess or assume your PD.

Occasionally, PD is written like 32/34.5 (for example), which means the measurement from the center of the nose to either eye plus your PD is the sum of the two – 32+34.5=66.5 (Mono R + Mono L = PD) and you can enter this as 66 or 67.

In your measurement, if you are off by a millimeter or two it's OK. Try to be as accurate as possible, especially for progressive lenses.

You may also be able to get your PD from a previous optician. Unlike a prescription, your PD does not expire with age. Opticians are required, under federal law, to give you your PD as well as your full prescription. It is considered to be your property. Once you have this information, you can then buy Discount Prescription Glasses online from GlasssesUSA.com.