Responses
I assume it's because his senses are maxxed out so he can feel what he writes without needing to see it physically
Visually impaired people iRL have ways to be able to write on paper. There's raised paper, tactile guides and bold pens, just to name a few. Not to mention the duke wasn't always impaired, so I suppose muscle memory could always help as well.
In chapter 2, when the aide introduced her to the duke. How is the duke writing when he is blind??? me is confused (´｀;)？