Do we know what happened to cause deafness?

It obviously had to do with the torture, and Josef knew there was a lot about her he didn't know, so it's not said exactly what was done to make her lose her hearing.

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"I think the mistake a lot of us make is thinking the state-appointed shrink is our friend"

I don't really see what Hanna's deafness did for the story. Indeed, there were moments when she didn't behave as one would expect for a deaf person.

Usually deaf people make solid eye contact when conversing, and use lip reading to reinforce what little they hear. But, for example, when she talks to her boss at the start of the film, her eyes are downcast most of the time. And just before that, while filing out amid the noise of others leaving with her, she hears herself paged to the office. Also, in a restaurant, would a deaf person eating alone be likely to overhear, in detail, a telephone conversation at another table? Aren't those times when she would likely have her hearing aid off?

Actually, when she tells her patient that she is deaf, my thought was that she was sort of putting him on, perhaps to get him to stop the distracting small talk.

I suppose her deafness sort of explains why she works in a factory instead of working regularly as a nurse, however. I wondered about that throughout the movie. I'm not putting down Sarah Polley's acting, she did a superb job, but maybe I have a few issues with the script. Making her deaf just seems a needless complication and tends to promote script discrepancies.

According to the description on netflix, the deafness was caused by workin at the loud factory -- this was later confirmed by a friend who worked on the set of the movie...