Try to describe the symptoms. Don't state the obvious, but how the words look to you on the page. Is there any tendency for them to jumble so that you seem to be having to chase the words while reading?
Or, is the page quite calm and still, but the words are simply difficult to interpret?
How is your spelling? What do you see in your mind's eye while spelling?
A great link for us word challenged.
http://www.wsu.edu/~brians/errors/