There can be a lot of confusion about frame sizing - what the numbers on the frame mean, and what size is the best for you. Let’s start at the beginning. You may have seen numbers stamped or printed on you frame, such as 48-17-135.
First thing to know, frame sizes are metric. Frames are designed, manufactured, bought and sold all around the world, so this allows a measure of consistency, regardless of where the frames came from, or where they are going.
The first number is the “eye” size, or the “lens” size. It measures the horizontal width across the lens in millimeters, from the “temporal” or outside edge to the “nasal”, or inside edge. This can also be referred to as the “A” measurement.
The second number is the “bridge” or “Distance between lenses (DBL),” which is pretty self-explanatory. The last number is the “temple length,” often popularly known as bows or ear pieces. This is generally measured from the hinge to the very end of the temple tip. As with any other item with a size on it, sizes can vary a bit – lenses can be a bit larger or smaller than stamped; bridges can vary.
So, we start with these basic measurements, but there are even more that the savvy optician will use to make sure your glasses will perform as expected. I mentioned how the horizontal lens size is also known as the “A” measurement; there is also a “B” measurement, which gives us the depth, or vertical measurement of the lens. This becomes very important when progressive “no-line” lenses are prescribed by your doctor – too short of a “B” measurement, and you may not be getting your full near correction, or may have to compromise on a lens design that has less intermediate vision than you expect.
The last number that can be useful is the “ED”, or effective diameter. This number takes into account all the various factors of lens size and shape, and specifies the smallest diameter lens blank that can be used to fit into the frame. While this hasn’t been a big deal for years with the smaller frames, the new larger designs will quickly make this number relevant again!
OK, so what is the “best” size? That, my friend, is a very complex question. The knowledgeable optician will take into account another measurement – your “PD”, or pupillary distance (how far apart your eyes are), compare that to the “frame PD”, which is the lens size plus the DBL, and then factor in your prescription to prevent lenses from becoming too thick, or induce too much distortion. They will also gauge the overall width of your head compared to your pupillary distance to help them select a frame that does not create dents in the side of your head, or make you appear to be cross-eyed.
The final factor in determining the best size is – fashion! For the last decade or more, the fashion gods have decreed that glasses have to be tiny. Thank goodness for all of us, frame sizes are slowly but surely getting larger again, making it easier to fit people with frames that actually fit AND look good.
So what is the best frame size for you? Ask an optician, and listen carefully to their answer. If they understand all the aspects of frame sizing, you could end up with the best performing, most flattering pair ever!