Hi there, I'm running a game jam event - Audiogame Jam - to raise money for the Royal National Institute for the Blind (RNIB). As interactive fiction is very accessible to blind computer users I thought I'd come here to promote it.

I'm also very curious of whether any devs. here have experience of making their game blind accessible through screen-reader support or OS-level speech functionality, or what proportion of your games' user base has sight loss.

While I don't have the answer to your question, I suggest also promoting your jam at this forum:

http://www.intfiction.org/forum/index.php

Also, you might be interested to know that the IF Tech Foundation has "measuring and improving IF accessibility" as one of its planned projects:

http://iftechfoundation.org/programs/

Thanks, I'll definitely post there.