Pretty sure this topic has never been approached. As I understand it, one of the main objectives of RR.com is to help others. I feel like I am walking on eggshells here, and am doing my best to avoid posting something stupid or offensive.
In my opinion, no scanner has ever been designed for the impaired and I doubt one will be.
If one is totally blind, I suggest the Uniden BCD396XT. Obviously, someone else would program it, but assuming it was programmed without assigining any system/group keys, it would be fairly easy to operate. One would only use the four buttons on the left column: "ON/OFF" "LOCK OUT" "SCAN" and "HOLD". The volume knob must be pressed to activate, and if it wasn't pressed, rotating it would not disturbed anything programmed. The "Menu" and "Fuction" buttons on the side would require a shield. Activting them and not being able to know what was happening couldn't possibly be to anyone's advantage.
If one has partial vision and requires a large, bright screen, a software program like Butel may be helpful. It has a Virtual Scanner feature which puts the scanner's display and keypad on the monitor. The only thing I am unsure of is the size of the font - some items could still remian hard to read if the font size is fixed.