can you be more specific about your disability? If it is severe dyslexia, for example, then this is not a problem at all. If it is something else then there is nothing to stop a person with physical or mental disabilities from passing the instructor exams as long as they can meet all of the requirements of the course.
But - and forgive me, I have to be blunt about this - if a person's disability should prevent them from being able to adequately teach or supervise student divers then the options for actually working as an instructor become more limited. If this is the case then I would suggest you contact dedicated disabled diver organisation such as the HSA, DDI, IAHD or SUDS. If you want further information, a good friend of mine is a Paraplegic PADI course director and disabled diving specialist. I'd be happy to put you in touch with him if you wish.
Cheers
Crowley