Four American women tackling Mount Everest have been forced to turn back just 285 feet short of the summit. Former heart patient Alison Levine of San Francisco collapsed and guide Lisa Rust developed vision problems in her right eye Saturday, according to Discovery Channel, which is chronicling the trip. All team members safely reached a camp. Since Edmund Hillary and Tenzing Norgay climbed Everest in 1953, about 1100 people have reached the summit at 29,035 feet. Only 11 American women have reached the top.