Well, some blind people can sense the light. And some blind people are sensitive to light too. I think the sunglasses can prevent their eyes from the damage of UV rays in harsh sunlight. We know that too much exposure to sunlight may lead to cataract. Thought blind people can't see things, but they also need to protect their eyes from developing cataract.
My grandma was blind too. But she used to close her eyes in the house or in the outside. But I have seen the person who opened his eyes while he couldn't see anything. I can't ask my grandma why she often closed her eyes because she passes away a few years ago. So I think the blind people use sunglasses to protect their eyes from being burnt by sunlight too. Just as what we do in daily lives.
We often blink our eyes to lubricate our eyeballs or close our eyes to protect our eyes when the sunlight is too bright, while some blind people can't sense the harsh sunlight and can't react to damages. Their eyes are easy to get further damages. So they need to wear a pair of sunglasses.
I think they may want to cover the appearance of their dull and unmoving eyes. The blind people also aware of their images too, so it is a good way to cover their eyes other than exposed this shortcoming in front of others. But I also think sunglasses can protect their eyes.
If you are very beautiful, and there is a person in front of you who stares at you all the time. You may feel uncomfortable. But if you know he or she is blind. You won't feel in that way anymore. So wear a pair of sunglasses can help avoid such kind of misunderstandings.
Sunglasses can make people look cooler. Blind people can use them to decorate themselves as well as cover their blind eyes. And when the blind people are talking with others, they won't need to worry about looking in the right direction.
Every time when I saw a person with this kind of striking decoration and hold a stick in the street, I would guess that he or she is blind. So I think blind people wear sunglasses to make them more outstanding. And other people will not run into him.