<div>I am unfortunate enough to be needing prescription glasses for driving as well as windsurfing. Being on the water, with sunrays coming from all possible angles, I chose Polaroid lenses. The cost of getting your lenses polarized is more than the frame itself
For windsurfing, good looks are not important as you are on the water anyway. Strength of the frame is very important though. I found a pair of cheap un-named frame from Japan. It has very thick frame and strong hinges. Also, its arms are also thick and strong. That pair of windsurfing glasses have lasted me for many years.
One of the major risks of wearing glasses on water, especially windsurfing, is it gets ripped off on waves, or when you do an involuntary somersault. I simply buy some elastic bands from supermarket. The kind of elastic you use for sewing purposes. I cut a suitable length form the roll, tie up the two end on the arms of the glasses. The "trucker's knots" is the best knot to get a firm attachment. Of course, you want the band to be just tight enough to keep your glasses on you head, but not so tight that it may hurt, or damage the arms of the frame. That will stop the glasses falling off 95% of the time except when and if your got rolled on waves.
Still, to ensure the glasses still with me if it does come off on waves, I tie a short length of nylon rope, a very skinny one of course, to one of the arms and to the zip of my wetsuit.
A little tip that may be useful: To check if it is Polaroid or not, get two pairs of the same, and line up the lenses. Rotate them about 90 degrees. If it turns totally dark, then it is a genuine Polaroid.