My advice: Spend the money on prescription glacier glasses. I mean, really, how much is this trip costing? In the scheme of things, paying the extra scratch for the right glasses will be trivial. The alternative is to wear contacts, but those can cause problems in the cold, dry, high conditions you'll encounter. And you WILL need glacier glasses. Yes, goggles too -- but for when it's windy and snowy. When the sun is out, glacier glasses are the deal.
So here's what you do: A Boulder, Colorado company called Opticus specializes in fitting mountaineering glasses with prescription lenses. You can find a pair that fit, such as Julbo Micropore's ($90), and send them in to Opticus with a copy of your prescription, and they'll make new lenses and fit them into the glasses. Or, just order a pair from them directly. They stock Julbo and Cebe -- the two big names in glacier glasses. Cost is typically about $250 for the whole deal. True, that isn't cheap. But I think you'll find it money well spent. Find Opticus at www.opticus.com, or call them at 800-870-5557.
They do prescription goggles, too.