Besides the function of protecting the eyes from the uv and other bad sun lights, the sunglasses now are regarded as the fashionable accessories which are not only used in summer. People wearing the sunglasses at fashion shows will just show their fashion by showing the cool appearance. Actually it is really a fashion for them.
Well, as a matter of fact, I personally have been to a lot of fashion shows, which is a good occasion to meet interesting people and get to know some new products in the market. So, by wearing sunglasses, they are less likely to be recognized because maybe some people have a secret mission. Or they simply want to appear more cool and maybe it is just their habit.
In my opinion, those people who wear sunglasses at fashion shows are both for cool and disguise themselves. You can wear your big ol' sunglasses while you're driving to the show. But, if you are elite status, you had better to pull them off during the show. In that way, you can enjoy a show perfectly.