This sounds exactly like my now DS7. I took him to a developmental optometrist and it has helped a lot. My Ds7 did not have dyslexia so much as a difficulty focusing visually on things. He would look at something and then look away. He also did the same thing as your son, with rapid fire reading and guessing at words. The vision therapy has been helping him persevere and we are seeing some positive improvements.
MAE is right about the cost of the developmental optometrist. I do scrounge the money whenever I take him. But, I figure it's worth it. The filters are a good aid, but I would not want to use something to compensate for a visual issue that could be corrected.
