I have impaired vision myself and I find HN to be one of the most accessible sites around. I have set all font sizes to 32-point and do not allow any smaller fonts. Also I have chosen a font that easy to read for me and do not allow sites to select any other fonts. On bad days I disable CSS so I can have my default bright-on-dark color scheme.

Using these settings, HN is a pleasure to read! Other sites suffer, of course, because large fonts destroy their layouts, but those sites are FUBAR (from an accessibility point of view) anyway.