It may be an idea for you to contact the medical department of the CAA to ask them. Too be honest, I'm not even sure if they can answer you, but perhaps they know somebody who can!
Medical Department
CAA Safety Regulation Group
Aviation House
GatwickAirport South
West Sussex RH6 0YR
Telephone: 01293 573700
In the mean time, perhaps somebody here can shed some light on it. My gut feeling is that it could be a problem in writing down clearances and the like, but I may well be wrong. Good luck!
T.