Are You Blind?

I use a white cane for identification, mainly when I'm traveling by myself or using public transportation.  It's funny how people see the cane and assume I cannot see at all.  On the subway I get people who come up to me asking if I need help or who tell me what train is coming next.  Most of the time it is just easier to thank them instead of trying to explain that I can see where I'm going.  It is nice to know that people are willing to help. 

There was one time when I was on my cell phone when my train came.  This woman grabbed me by the arm and tried to "help" me on the train.  I have to admit, this took me by surprise and I was not very polite.  I shock her off and told her "Get off of me!"  I probably would have been nicer if I hadn't had such a bad week.

More recently, I was on the train and right as I was almost to my stop a fellow passenger asked me "Are you blind?" (she must have seen me look at my watch)  There is not a short answer for that question.  Yes I am legally blind which means I have less than 20/200 vision in my better eye.  But most people assume that blindness means you can't see anything.  If I hadn't been about to get off I would have tried to explain all this to her.  Instead I just said something like "I have some vision.  I can see a little bit."  I want to take every opportunity to educate people about people with disabilities but I realize you can't always take time out to lecture people.  Sometimes you just have to let it go and let these people go on thinking what they think.  Any thoughts?