BALTIMORE - Sitting on the front steps of her Cockeysville, Md., home a year and a half ago, Vanna Belton was startled and thrilled when her eyes focused on a car's license plate. Essentially blind for more than five years, she suddenly could read the numbers and letters.

"When I realized I could see the license plates, we started walking around the neighborhood reading them," said Belton, recalling the excitement she and her fiancée felt at that moment. "We drove around and read store signs. The Pennsylvania Dutch Market. The tanning salon."

No one can explain exactly how Belton came to see again, not even the doctor who treated her as part of an unconventional stem cell study shortly before she regained limited vision.

Despite their promise, stem cell treatments often garner skepticism from experts who are still studying their safety and effectiveness. While stem cells can be grown into any type of cell in the body, scientists generally believe proving the cells can repair or cure anything is a ways off. The only U.S. government approved stem cell treatment involves blood clotting disorders, but that hasn't stopped those who can afford the treatments from seeking them.

An unorthodox study

Belton, now 29, was training to be a police officer in Washington in 2009 when, while stuck in traffic one day, she noticed the streetlights were blurry. Weeks later she had almost no vision and no explanation for why everything seemingly went dark.

She was diagnosed with a sudden and perplexing case of optic neuritis, a general term meaning optic nerve inflammation.

Belton's damaged optic nerve was not properly sending visual information to her brain. Doctors suspected the cause was multiple sclerosis, an autoimmune disorder, but Belton tested negative for it. They initially said her sight would improve, but after six months they stopped calling her blindness "temporary," she said.

Since doctors offered little hope and no treatment options, Belton turned to Chinese herbs and acupuncture and even made a trip to India seeking a stem cell treatment.

After relying on friends and family for help getting around, she learned to use a cane, public transportation and technological aids for the blind. One such aid helped her access a dating website and she met Julia Donoghue, who would become her girlfriend and later her wife.

Their first date was at Ruth's Chris Steak House, where Belton once worked. It was a familiar enough spot to initially hide the fact that she could see little more than shadows. Things went so well that she mustered the nerve to tell Donoghue about her condition. They began dating, enjoying meals and walks together with Donoghue holding Belton's elbow. They also devoured any research they could find online about her condition.

As Belton searched for alternatives, a doctor pointed her to clinicaltrials.gov, the National Institute of Health's clearinghouse of studies. There she found Dr. Jeffrey Weiss in Margate, Fla., who was enrolling blind patients in an unorthodox stem cell study.

He wasn't affiliated with a university or government institute, but he was taking on all those who could afford the roughly $20,000 to pay for the study and injecting stems cells into their eyes in one of three ways - around the retina, in the retina and directly into the optic nerve - in hopes of restoring some people's sight.

He made no promises.

Her local doctors advised against it; one doctor even called her stupid. Belton decided to go see Weiss anyway.

She paid for it with her wedding budget, opting instead for courthouse nuptials, and a few weeks later in early 2014, she had the surgery. During the four-hour procedure, Weiss and a medical team extracted bone marrow from Belton's hip, separated her stem cells in a machine and then injected the cells in and around her right eye's retina and directly into her left eye's optic nerve.

Weiss is not following the usual steps of clinical studies. Among other things, he didn't test his treatment theories first on lab animals or using computer models, or randomize his trials by using either stem cells or placebos in study participants. He didn't test the procedure for safety on a small group before moving to a larger trial.

Weiss, who is board-certified in ophthalmology and once taught at Harvard University, said he didn't have the patience for academic research, which is strictly governed by internal review boards and requires fundraising. Without a long history of stem cell research and a current academic appointment, he said, he sought legitimacy for his work by registering the trial with NIH, which scientific journals require to publish promising results.

Not sure how it works

The U.S Food and Drug Administration must permit the use of "investigational" drugs, and the NIH requires that researchers attest they have such permission to register a trial. While the FDA continues to tweak regulations, there are exceptions when stem cells aren't considered drugs, such as when they are minimally processed and taken from and used in the same person.

The NIH also requires researchers to gain approval and oversight from an ethics review panel. Universities and government agencies have their own panels; Weiss tapped the International Cellular Medicine Society, an independent group that promotes stem cell therapies.

Weiss published a case study about Belton in the journal Neural Regeneration Research. However, he said, 60 percent of his 278 patients with macular degeneration, glaucoma and other diseases have regained some sight.

While he can't explain how it works, he believes that will become clear eventually.

"We didn't know how penicillin worked for many years, but it saved many lives in the meantime," Weiss said. "It is hubris to think that something can't work until you understand how it does. … It is more important what the patient sees, not what I see."

No one disputes that Belton now sees well enough to read the menus in her new Mount Vernon restaurant, Flavor. She can navigate the eatery and the streets without the white cane she once used. And on her wedding day, just a week after she read the license plate, she could see her wife's face.

"She started crying when she realized I was looking in her eyes," Belton said.