Well, I assume that some research effort has been put into translating into speach for visually impaired. Of course the input may already need to be logically structured (LaTeX, MathML, ...), not just a scanned image of symbols, as otherwise the fine typographical destinction between $2^{2^3}=256$ and ${2^2}^3=64$ might be hard to handle. Finally, how would one translate $A\rightarrow B$ out of context? The arrow can have many different meanings and should not just be read as "rightarrow". Not to mention author-specific conventions ("In this text I shall write ... to denote ...") –  Hagen von Eitzen Sep 2 '12 at 8:06