See as how I have a larger head, I figured that 54mm was a wise choice. My girlfriend has a smaller more round-shaped head than myself and the 51mm frames look perfect. Proportionally speaking, the 54's look just as good on my face as the 51's do on hers. So if you have a longer or larger head definitely go with the 54mm frames.<br /><br />These are very similar to the black solid frames. I would say that the translucent part of the frame makes this seem a bit more flashy or glossy. I like these because they appear SLIGHTLY less casual than the traditional solid black frames -Yet, they still look great with casual attire.