South Dakota Rehabilitation Center for the Blind student, Brandi Vissers, 20, of Sioux Falls, who has retinitis pigmentosa--a degenerative eye disease that causes severe vision impairment and often blindness--works on her ability to find the edge of a curb and prepare to cross the street with Bob Smith, an orientation and mobility instructor at the Rehabilitation Center, 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.