You have to use polarized sunglasses when out on the water.  I find an amber lens gives me the best distinction between shallow and deeper areas.  I also like a frame that wraps around my eyes.  The issue of the wrap-around is the fogging of the lens.  I have found frames that works for me, but every face is different.  Take you time to get a good frame and lens that works for you.  Your eyes are the best tool to navigate the shallow waters of the Florida Keys.