Once I got a Kindle I fooled around with settings and tried out all the fonts. Was surprised that there was one that was not "annoying" and let me read faster.

Fast forward a few years and I've had my eyes checked and found that I have mild astigmatism (0.25 left and 0.5 right).

Now I have a font that I can still read without glasses (but mostly in bed and with slightly larger text).