Multiple icon themes have been introduced in Gnome2. Some of these have been designed specifically for better accessibility.
The simplest of the set is Large Print which is essentially the Gnome stock theme drawn at a larger size.
For a certain group of people a Low Contrast version of this theme has been made (programatically). It's targeted at users who are very sensitive to luminosity differences and thus prefer low contrast themes.FIXME
Figure 1.1. Accessible icons. From left to right — regular stock icon, large, large low contrast, high contrast, high contrast inverted.
The last of the acessible themes is the High Contrast set, which this document describes in more detail. High contrast and scalability typically overcomes the refractive vision error (“unfocused image”). There is a variation of the theme available where the colors are inverted, called High Contrast Inverse.