I got to know a blind person (I'm pretty sure he became blind at an older age), who would Daven the whole Davening out loud. Eventually it made me think, if I ever go blind I won't be able to Daven, so for the past bunch of years (probably around 10 years), I've been Davening out loud and by heart (with a Siddur always next to me "just in case"), at this point I can pretty much Daven all general Teffilos by heart.