i suppose its like dyslexia, the level of difficulty one has.. if the issue was that you were not able to read the numbers and make mistakes, example read 2 as a 5, and 9 as a 6 and so on, then my opinion as we all have, the person is not safe, if it were that the person could not do calculation very accurately, then the calculator become ones friends, we all used one at one point in the cockpit.
Bu things such as altimeter, speed, and altitude would be unsafe, and the caa i would have thought would question the physiology of the pilot.
I would advise this is just my view, and no disrespect intended but that's how i would view this issue..