'Unsighted' and 'blind' mean exactly the same thing. The only difference is that you almost never see 'unsighted' used. 'Visually impaired' is not necessarily blind. It refers to any eyesight where the person has trouble doing everyday tasks. It could be fuzzy vision, vision where part of the field of vision is blocked, etc. It does not refer to somebody, say, who has to wear reading glasses. If I wear the glasses, I can do anything a person with perfect vision can do, therefore, my freedom and ability to do normal things is not diminished.

Correction: What's the difference between unsighted, blind and visually impaired? Do I offend people when I say blind? How about disabled and handicapped? Is one of them more polite to say? Thanks! The verb is "to offend", the noun is "offense", and the adjective is "offensive."