Over the last month, Horgan and other surgeons at the University of California, San Diego have performed more than 20 minimally invasive operations while wearing Apple’s mixed-reality headsets. Apple released the headsets to the public in February, and they’ve largely been a commercial flop. But practitioners in some industries, including architecture and medicine, have been testing how they might serve particular needs. Horgan says that wearing headsets during surgeries has improved his effectiveness while lowering his risk of injury—and could have an enormous impact on hospitals across the country, especially those without the means to afford specialty equipment. “This is...