I use to work with someone who had been blind since birth, we worked together for a couple of years........ I use to provide IT support for him helping him with speech synth stuff on his laptop etc blah blah bore. Anywho, as we became friends this was one of the topics we discussed. He told me that he dreams all the time and that they were visual dreams, he explained that he still has pictures of what everything looks like in his mind (despite not having ever seen the object), he creates the pictures through his other senses. Although he did admitt that his pictures may not be as accurate as the real thing but pictures and dreams do exist in the mind of the blind.
Quite an amazing person, very inspiring to see someone with what I consider to be a big disability in life and to still have such a lust for life and a great attitude.
Off topic, Funny story: The first time I had to do a support job for this person I was informed that he was blind and required help with blah.... So I went to his office and on arrival found that he was not in. After completing the job, I found a post-it note and pen, scribbled a brief message and stuck it too his laptop to inform what I had done and to call if there were further issues. About an hour later he must have found the post-it note as everyone in the building received a mail from him requesting "If the person who left me (the blind guy) a post it note on my screen would kindly come back and read it to me".
From that day one we always laughed about it