As livndisney and Cheshire Figment posted, WDW has Guest Assistance Cards that are meant to assist with needs related to a disability. The cards are not given "for medical conditions" or by diagnosis, but based on the needs someone has related to a disability.
They are not Fastpasses and actually printed on the card it says that they are not meant to shorten or eliminate waits in line and if you want to shorten your wait in line, you should get Fastpasses.
Besides the information in post #6 of the disABILITIES FAQs thread about Guest Assistance Cards that Cheshire Figment and livndisney mentioned, post # 3 of the disABILITIES FAQs thread has information about touring with epilepsy/seizure disorders.
Since this was answered and the OP was pointed toward references, I am closing this thread.