Purdy accomodates this sort of event. At ACRES he discussed similar 'disease' in deer and elk in Colorado. The source, he believes, is heightened manganese concentrations in pine needles in the area. I've forgotten the details, but, overall, it's the degeneration of the soils, the rains, the trees, and the deer and the sky that work together to cause this neurological breakdown. Increased ultraviolet reacts with increased manganese in the eye to excite the production of prion-like substances.
ACRES does make a tape of Purdy's presentation available http://www.acresusa.com (may not be explicitly listed. Call them if you need the tape.) -Allan
