Out of 18 legally blind patients with progressive eye diseases, more than half reported greatly improved vision after having human embryonic stem cells infused into their retinas.

"I'm astonished that this is working in the way that it is — or seems to be working," Steven Schwartz, a UCLA eye specialist who led the study, told NPR. "I'm very excited about it."

The study participants had age-related macular degeneration and Stargardt's macular dystrophy, the leading causes of blindness in the developed world. Researchers did not expect the patients to regain any sight, and were just trying to determine if it was a safe procedure.

Human embryonic stem cells can become any type of cell in the body, and researchers turned them into retinal pigment epithelial cells. Between 50,000 and 150,000 cells were infused into the retinas of patients, replacing dying tissue with new tissue. Soon, 10 patients could see significantly better, seven saw better or didn't lose any additional vision, and one was worse. "These are patients that didn't see better for 30 years and all of a sudden they're seeing better," Schwartz said. "It's amazing."

The results were the first for any human embryonic stem cell trial approved by the FDA, but they're considered preliminary because the number of patients treated was very small, and they were only followed for an average of less than two years. Many said their lives have changed for the better — one elderly rancher can ride his horse again, and a consultant who travels internationally is able to walk unassisted through airports — but Schwartz notes that the procedure is "not ready," and won't be for at least a few years: "We have to wait and see. The jury is way out still."

The findings were published Tuesday in The Lancet. Catherine Garcia