Riddoch syndrome is very rare, and thus not especially well understood. It is however a disorder related to motion perception, not coordination of movement based on perception, so not optic ataxia as such.
There was a story on All Things Considered today (26 May 2014), about a Scottish woman who has Riddoch syndrome, due to stroke induced damage to her visual cortex. The parts of the brain responsible for normal visual perception no longer function is the patient, but she can see motion with enough clarity to see the shape outline of moving objects, but she cannot perceive any details (color, contour, etc.) Using a rocking chair, to put non-moving objects in relative motion to her head, she has improved her visual motion detection, and can now do it just by moving her head voluntarily.