Three elderly women with a common age-related eye disease were blinded after receiving stem cell injections at a South Florida clinic in the summer of 2015, according to the New England Journal of Medicine this week.

The cases raised red flags about the procedure, according to Thomas Albini, a clinical ophthalmologist with the University of Miami Health System’s Bascom Palmer Eye Institute, the Miami Herald reported Thursday.

Each of the women had both eyes injected on the same day with stem cells extracted from their body fat. They received little to no follow-up care or evaluation before or after the treatments. And they paid $5,000 each for the procedure.

“When that all was revealed, I was just in disbelief that this was happening,” said Albini, who helped care for two of the three women and co-wrote an article about the cases in this week’s New England Journal of Medicine detailing his experience.

“I knew that things like this could happen in other countries that don’t have a sophisticated medical regulatory environment,” Albini said Thursday. “But I really was naive to the fact that this could happen in the United States. Then I realized I was just as naive about it as the patients were.”

Albini’s article, co-written with nine other physicians, exposes what he calls a “loophole” in the U.S. government’s oversight of unproven treatments involving stem cells. It also raises questions about whether federal regulators are doing enough to protect patients from risky medical procedures .

He said he co-wrote the article to alert physicians and patients to the dangers of unwarranted claims about the healing power of stem cells, which Albini said hold promise but remain largely untested for clinical use.

In a written statement, Mike Tomás, CEO of U.S. Stem Cell Clinic, called the NEJM article “old news” and suggested it had been published to challenge the company’s most recent financial report that revenue had risen by 38 percent, from $2.2 million in 2015 to $3.03 million in 2016.