I usually wear contact lenses, but I do have glasses as well, and sometimes I prefer to wear them. I definitely did need new ones after I'd lost a good bit of weight, because I was having the same problem; they kept falling down my face. You may be able to have them tightened up, but I also found that the old glasses, picked to suit my giant moon face, just weren't flattering with my much thinner, far more angular face, so I ended up getting a totally different style of frame for my new ones.
Began 14 August 2008
Initial goal of 175 reached 5 July 2010
Goal reset to 160
Maintaining 160-165 since November 2010