Do you have one of these new fangled Verification Graphics in the comments section of your blog? I think it is meant to stop spam. Well it also stops visually impaired people leaving comments too!
Blind people can't read graphics with their screenreaders at all ... and partially sighted people mostly find it too difficult to decode what the graphic says. So there's no way that visually impaired people can tap the word into the edit field because we can't read it!
I urge you, if you have this anti-spam feature on your site ... dump it immediately!