My Deaf Actors on Star Trek post got good comments, and yes, I'm familiar with how the show is fantasy and sci-fi. Some of the storylines have reflected real life to an extent. Some things have become reality, as their communicators have become today's cell phones and PDAs to name a few things.
However, even though it's set in the future, with the the occasional mention over time of how the common cold was eliminated as well as a few diseases, there's always the subject of disabilities that you almost never see. In the original series, Captain Pike is in a wheelchair-like device after an accident in "The Menagerie, Part I" (first season, episode 15) in November 1966.
We also see Bill Cobb as Emory Erickson in a wheelchair in Star Trek: Enterprise in the fourth season, tenth episode, due to a transporter accident.
Consider for a bit that if certain disabilities were not quite eliminated, but helped to an extent. How would other deaf communicate with the computer and other people? Would they type and read the responses? Would they have duties on the bridge as well as other key areas on the ship? One might also have an interest in the subject of bionics, which could be used on those with hearing losses. They could be used in the Star Trek time frames, and they have.
One interesting thing... A commenter in that previous post mentioned a beautiful empathic woman with incredible healing powers. That would be The Empath on the original series (season 3, episode 8) in December 1968.
Kathryn Hays played the empathic character and is still performing today in her 70s.