Every time I see a blind person in public, they always use a white cane and wear glasses. If they can’t see, why do they wear the glasses?
Sometimes, the person is not totally blind but is sensitive to light. For example, last month, one of the reporters at a presidential press conference in the Rose Garden was wearing sunglasses and the president made a couple of jokes about it. Later it was revealed that the reporter is legally blind and sensitive to light, which is why he was wearing the sunglasses. (To be fair, the president wasn’t aware of that at the time and apologized when he found out.)
It could be because their eyes are unusual looking because of their blindness (whitened corneas, completely closed pupils, etc.). It could be because they know their eyes wander around and they don’t want people to mistakenly think they are staring at something inappropriate. And it may just be part of the way you communicate “Hey, I’m blind here”.
I think the white cane lets people know.
It may not apply to the average blind person, but entertainers are “managed” by people who let them know that their eyes don’t “look right” to their audience. If you ever see (or saw) people like Ronnie Milsap, Stevie Wonder, Ray Charles, George Shearing, Rahsaan Roland Kirk, etc., without their glasses (usually shades) you’ll know how unsettling their eyes look.
In short, the glasses are for cosmetic purposes.
As Dewey Finn mentioned, many (perhaps most) blind people do not totally lack vision. They may be able to make out the general shape of large objects, which is a very useful ability (if that large object is a car, for example, it might just save their life). Direct sunlight on the retina could easily damage what little eyesight they have, so they’d want to avoid it.
I’d imagine that sunlight could be an even greater concern to blind people than people with normal vision. A blind person might not be able to immediately tell that he/she is looking directly at the sun, so might not glance away before the damage is done.
I just happened to be researching photophobia (sensitivity of the eyes to light) recently, and what I found is that many of the diseases/conditions that cause blindness will make the eyes photosensitive - which means not only that they sense the difference between light and darkness, but that the sensation of bright light can be uncomfortable or painful. Thus the need to protect the eyes.
It should also be pointed out that some blind people actually don’t have eyes, and for whatever reason, don’t use glass eyes. Do you want to be staring into someone’s empty eye sockets?