Bob Smith, an orientation and mobility instructor at the South Dakota Rehabilitation Center for the Blind, demonstrates how to find the edge of a curb and prepare to cross the street with student, Brandi Vissers, 20, of Sioux Falls, who has retinitis pigmentosa--a degenerative eye disease that causes severe vision impairment and often blindness--on Wednesday, April 9, 2014, at the corner of 28th Street and South Willow Avenue in Sioux Falls. Smith said that he can teach students how to use indicators, such as the terrain in Sioux Falls, to find their way around town. (Joe Ahlquist / Argus Leader)