It is a personal decision to tell another person, agency, company or institution about your disability.
Disclosing your disability is not legally required by an employee EXCEPT where it affects your ability to perform the 'inherent requirements' of a job (for an explanation go to section on Disability Discrimination), including to work safety in the workplace.
Telling others about a person's disability is reported by people with disability and their families as one of the most difficult aspects of living with a disability. It's a hard decision to make and so much hinges on whether, how and when they disclose.
Each transition stage in the life of a person with disability raises disclosure dilemmas. The transition out of university or TAFE and into graduate employment is for many people with disability their first venture into the professional world. This is a big move and raises questions about whether and how the graduate's disability will affect them in their new role as employee, and how prospective employers and co-workers may react to the person's disability.
Having a disability that is apparent to others doesn't mean there is no disclosure dilemma. There may be other aspects of the person's disability that are not apparent to others, such as a degenerative condition, an underlying medical condition or other disabilities not visible.