How can you make an interface for impaired vision that works for you and other people?

If the interface is for impaired vision, firstly consider whether vision is the best medium in which to work. It may not always be. (rather than making a clock more visible, how about a talking clock?)

If for people with poor vision, remember BBB

Make it

Big... increase size of characters, wherever possible. This may be limited by the number of words that need to be displayed.

Bright... Good illumination. Really good illumination on printed material can deliver an improvement in print legibility of two or three sizes.

Bold... High contrast, with no fussy confusing backgrounds or unecessary images. No coloured print on a coloured ground. White print on black is often more legible than the conventional reverse.

That would generally be fine for ordinary vision too, except if the print has to be so large that more pages have to be used on the booklet/screen etc.