You can wear sunglasses when attending triathletes. Sunglasses can protect you eyes from sunshine.Polaroid sunglasses are most suitable for triathletes. Because this kind of sunglasses can effectively isolate you from the glare and you won't influenced by the hardlight. By the way, wearing sunglasses make you concentrate on the competition.
You must wear sunglasses when you are doing triathletes to protect your eyes from bugs and other foreign matter when they impact at 30kph or faster. Glare is not in the consideration in choosing triathletes sunglasses. Neither are frame and style. Besides, your sunglasses should be comfortable to wear, so it is better for you to purchase triathletes sunglasses in a physical store rather than online. To make sure that your vision is not blocked, you'd better choose frameless sunglasses. I'd like to recommend NASHBAR NO-FRAMES to you. Here is its official website:
https://www.nashbar.com/bikes/Product_10053_10052_169399_-1_201492_10000_200442. You can get detailed information on it.
Yes, you can wear the sunglasses when you attend to triathletes which will improve your cool look and help you protect from the uv rays in the strong sun light. You could choose the ray ban classical types which could be suitable for you. You could go to the real store to have a look at the products which may be perfect for you to wear.