Here is a very interesting 2002 article on blind mathematicians from the Notices of the American Mathematical Society. Some quick highlights:
1) Although Lev Pontrjagin is the best known blind mathematician -- and was a wonderful mathematician; "who made important work in topological groups and control theory" is quite true but may be an under-sell -- there have been others. If we count mathematicians who were blind for a substantial portion of their professional career then even Pontrjagin gets outclassed: there is, after all, Leonhard Euler. And there are more contemporary examples, such as Bernard Morin and Lawrence W. Baggett. Both of the latter are still living but retired (on the other hand, the article is 12 years old). It would be interesting to have even more contemporary examples.
2) Being a blind mathematician is rare but not singular. In fact there are enough to notice that blind mathematicians tend to specialize in geometry and topology. This is very surprising, as these fields are thought of as requiring visualization skills beyond the norm (I for instance have felt a little locked out of certain parts of geometry and topology because of my limited skills in this area....though my vision is fine). The article really shines in the way it addresses this point: the insight it offers goes far beyond, um, sight. At the same time there are blind mathematicians in other fields: e.g. Baggett is an analyst.
3) Blind mathematicians must in many ways work harder than sighted mathematicians. But of course mathematics is hard for everyone, and much of being a successful mathematician is embracing the struggle and continually pushing yourself out of your comfort zone and beyond your current range. This is a key point of Terry Tao's career advice. For that matter, I am suddenly struck by Andrew Wiles's famous description of mathematical research as exploring the rooms of a dark house one by one: you spend almost all of your time in the darkness; when you find the light switch you flip it and go on to the next room. (I don't mean to trivialize the challenges of literally living in the dark, just to indicate that the experience of dealing with and gradually surmounting challenges that to a static observer seem totally insurmountable is a somewhat familiar one.) Reading this article made me wonder about the OP's assertion "this person would probably need an assistant for continuing doing his/her research and for giving lectures at some extent." Some might need or want a formal assistant, but some might not and might be self-reliant and of course reliant on the informal assistance of colleagues, friends and family...as we all are. The mathematicians featured in the article are much more independent than one might have assumed possible.
The question was not specifically about blind mathematicians, but that was the example given, and I am a mathematician, so I ran with that. Off the top of my head I would suspect that blindness would be less of an issue in mathematics than most other academic fields...but as a sighted mathematician, how the heck could I possibly know that?!? I would be very interested to hear about blind academics in other fields and what challenges they face.