I have what seems like a similar problem, but pointing at what I'm reading or using a sheet of paper does not work. Strangely, I find it hard to read newspaper articles and long forum posts, but books are fine. I have wondered if this is something to do with how long I expect it will/should take to read it.
So, someone passes me a newspaper article and says "here read this, I really think you will find it interesting!". Even though it is squished into neat little paragraphs with only about three words per line, which is designed to make it easier for people to read, I look at it and get a feeling of dread. I just don't want to read it. If I try, it usually doesn't make much sense.
When browsing through a forum thread, I often skip past the long ones, and again, if I do try to read them, they won't make as much sense as the short ones.
Those two scenarios don't really have that much in common yet they have the same effect. What might they have in common? Pressure to read them quickly or within a certain amount of time? Sometimes I am in a really relaxed state when I read forum threads, with the purpose of gathering particular information, rather than just "getting up to date on a topic". I find the longer threads easier to read when I am in this relaxed state, I think.
So, books. Nobody is going to pass me a book as say "here, read this now and tell me what you think!". Usually I choose when to read a book, and without the purpose of finishing that hour, or that day. I finish it when I finish it. I love doing it, and the content makes sense.
None of this may have anything to do with your issue (or even mine, it's really just a thought), but I thought I'd mention it in case it resonated.
Maybe this post was too long to read though