When I was studying math, a lot of times, I got to take tests at home. Prof would email me a copy of the test in LaTeX (they used it anyway), and I'd mail my answers back in LaTeX or PDF. Worked well for us. I'd just slip out the door on test days, walk the three blocks to my apartment, type up my answers, and mail them back.

In one case, one of my profs actually wrote his own textbook. It was for an intro to theorem proving / symbolic logic class. He also used LaTeX. While everyone else got a printout of the course text, I got a copy of the source code that I could read with a screenreader.

I'm a disabled student, not blind, but I work extensively with my university's Student Disability Center. For a blind student, common accommodations are extra time on the exam and a scribe to note the answers down.

You might be interested in this overview of strategies: http://itd.athenpro.org/volume1/number4/article3.html

Although in practice the answer is that instructors have to lean heavily on the learner and the university's resource center.

My understanding is they give a proctor and provide assistance. How a student declares their solution is an interesting question though.