 For those who need corrective eyewear, three out of four adults in this country do, the choices seem endless. But shopping for new specs and contacts can be a hassle, and it can be expensive. Consumer man Herb Weisbaum, a contributing editor at Checkbook.org, has some money-saving advice. It seems like there's healthy competition for eyewear, with dozens of major chains all selling dozens of brands of glasses, maybe hundreds of different frames. But here's a little secret. That competition...