Toby Willis gave up on medical miracles long ago.

The Seattle man’s eyesight started deteriorating when he was a kid and by the time he was in his early 40s, his visual world had dimmed to shadows.

Still, he refused to obsess over scientific advances. “I made it a point not to go down those rabbit holes, to be chasing that pipe dream,” he said.

Nevertheless, the possibility that something might be on the horizon occasionally tickled at the back of his mind.

So Willis checked in with his eye doctor late last year, setting in motion a train of events that culminated in becoming the first adult to undergo the first gene therapy approved in the U.S. for treatment of an inherited disease.

The medication, called Luxturna, is injected in the eye and uses a harmless virus to deliver working versions of a gene to the cells of patients whose own genes are defective. It targets a single, rare mutation, but has raised hopes that after decades of disaster and disappointment, a wave of gene therapies for other disorders is on the way.

But Luxturna’s staggering price tag of $425,000 per eye is raising questions about who can afford the newest medical technologies — and whether the results will justify the costs.

Willis already knows it won’t be a miracle cure for him. The therapy is expected to work best in children with early diagnoses, before the disease causes irreversible damage. In Willis’ case, doctors hope it will keep the 44-year-old software engineer’s eyesight from getting worse and perhaps improve his ability to distinguish objects and navigate the world. Without the surgery, he would eventually lose his eyesight entirely.

“As much as I would love to have a full range of 20-20 vision, that’s not realistic for me,” Willis said. “But to be able to recognize my fiancée’s face or see my guide dog, or maybe enjoy a more rich experience in my travels and hiking — that would be a big deal.”

For physicians who have helplessly watched patients go blind, even an imperfect treatment represents a breakthrough.

For gene-therapy researchers, it’s a thrilling validation.

“I think this is a game changer,” said Timothy Cherry, who’s exploring ways to repair inherited forms of blindness at Seattle Children’s Research Institute. “What I see as inspiring is that this shows us that the fundamental idea works.”

Gene therapies for several other inherited diseases are already in the pipeline.

The Luxturna procedure takes about an hour and requires precision, said CHLA Vision Center surgeon and researcher Dr. Aaron Nagiel. With a tiny light illuminating the inside of the eyeball, he had to thread a needle through a port and inject a .3 milliliter drop of viral solution between two layers in the retina where the RPE65 gene carries out its mission. If something goes wrong, there’s a single backup vial.

In clinical trials, 27 out of 29 patients experienced improvements that lasted at least a year, and more than 70 percent were able to navigate better in very low light. One patient’s vision got worse. But some experienced dramatic revelations, like seeing the stars for the first time.