You will be at high altitude while trekking in the mountains or desert where a pair of best trekking sunglasses is of great use. And wearing a pair of carefully-chosen sunglasses will for sure make you cool on the trail. And the most important of all, the sunglasses you wear should protect your eyes from intensive sunlight and reflective glare. So your sunglasses for trekking should be of strong frame and polarized lenses. Now the most popular sunglasses for trekking in the sunglasses market include Oakley Straight Jacket Sunglasses, Chili's Bluefin Polarized sunglasses and Maui Jim Ho'okipa Sunglasses sunglasses from which you can choose the one suiting you. And of course there are many other nice ones for trekking. Just have a look at all of them and pick up the right one. And at last I wish you a pleasant trekking.
Your sunglasses should have the function of protecting your eyes from UV. The lenses can't be too light and be sure that you can't see your eyes clearly in the mirror with the sunglasses on. A "wrap-around sunglasses" that protect your eyes around all sides is suitable. Choose sunglasses with interchangeable lenses so that you can change lighter shade lenses on cloudy days. Your sunglasses should also light in weight in order to avoid hurt on your nose after a long time of trekking. For fear that your sunglasses break or are missing, head strap that enable you to attach sunglasses on the neck is necessary. I'd like to recommend two sunglasses to you:
Native Eyewear Hardtop Polarized
Oakley Flak Jacket Sunglasses (http://www.oakley.com/products/4658/15247)
Ok, from what you said, I know what you want to do, and your goal just requires a pair of nice and solid sunglasses which could help you with UV rays. Because as you can see, in the open, especially on a sunny day, your eyes are likely to get burned by the sunshine. So, your choice of sunglasses must consider more the quality rather than the design you know? Try to take a look in a local optical store and consult a professional clerk.