Hello upnseams. You mention having a visual impairment. These threads may be useful:
Low Vision Guide to the PRS-505
https://www.mobileread.com/forums/showthread.php?t=39757
PRS-505 text zooming
https://www.mobileread.com/forums/showthread.php?t=37563
(in which some people note that the Cybook has more zoom options than the 505.)
Very poor vision level, which reader?
https://www.mobileread.com/forums/showthread.php?t=39165