Firstly, ask your eye doctor or assistant to help you record your PD (or Pupillary Distance) measurement on your glasses prescription. This is a simple measurement that they can take which is the distance between the centers of your pupils and is recorded in millimeters. Your eye doctor normally would use a machine that can automatically record the PD measurement while you look into a binocular-like device. The average adult’s PD measurement is around 63mm while a child’s measurement is around 54mm. If you get a separate measurement for your right and left eye, simply add them up to get your PD measurement.
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Then, Take some measurements of your existing frames, especially if you have a particular frame that you like. Oftentimes, you will notice that the measurements are stamped inside the temple or on the bridge. Usually, there are 3 measurements in such a form: 52 18-139. 52mm being the (eye size) Lens Width, 18mm being the (bridge size) Bridge Distance and 139mm being the Temple/Arm Length. Another important measurement is the lens height which you should take manually. Some people prefer shorter lens heights while others prefer larger lens heights. cheap prescription glasses should have a minimum lens height of 26mm. When choosing a frame online make sure the measurements of the frames you are perusing are similar to the measurements you have taken of some of your existing frames. But remember, the measurements do not have to be exactly the same. It is only a good guideline, so you do not get frames that are grossly too large or too small for your head size. If you don’t have any existing frames, or this is your first pair of eyeglasses, you may find a nice fitting pair or two at your local shop, and record the measurements down. Remember, the measurements should be stamped directly on the inside of the temples.
Last but important, Input your prescription details onto the given form and choose the appropriate lens for your frames. If you don’t understand your prescription, send an e-mail to your online vendor to see if they can decipher it for you. As a general rule if your sphere power is between +6.00 to -6.00 you can use the mid-index 1.56 lens. For sphere powers between +6.00 to -8.00, thin index 1.61 lens may be appropriate. For sphere powers between +8.00 and -12.00, high index 1.67 lens are recommended. Ultra high index 1.74 lens may be needed for more extreme sphere powers due to the thinness of the lens. Your lenses should include, anti-reflection coating, anti-glare, anti-scratch and UV coating. If you require additional lens surfacing, such as Photo chromic lenses that darken when exposed to the sun’s UV rays or need Polarization, you may ask your vendor if they offer this service.
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