Dr. Chakrabarti said that if Chaudry kept his eye, he could still lose his life, since surgeons couldn’t remove the thin layer of infection behind his eye without removing the eye itself. “I’ve lost vision in my left eye, my studies have suffered,” Chaudry said. The study that Dr. Chakrabarti co-authored, published this month by the U.S. Centers for Disease Control and Prevention, said that heavy use of steroids, the correlation with diabetes and the unsanitary conditions at some hospitals had played a role. Even before the pandemic, India recorded about 50 mucormycosis cases a year, compared with, on average, a single case every two years in the United States and Western Europe. Environmental conditions play a part, as does the incidence of diabetes — India has more than twice as many people with the condition as the United States does. In India, mucormycosis afflicts people with diabetes who are either unaware of their condition or who are not taking insulin properly. But in the current outbreak, many patients had no history of diabetes. The common denominator was a COVID-19 infection treated with steroids, clinicians and researchers say.