“Glasses can usually return you to 20/20 while hearing aids don’t return you to normal hearing, not even close,” said Kathleen C.M. Campbell, a professor at Southern Illinois University School of Medicine.

Image The trial at the University of Kansas Hospital uses a gene therapy developed by GenVec, a Maryland biotech company. Credit... University of Kansas Hospital

But challenges remain. Efforts in the past to develop ear drugs, to the extent they were made, largely failed. The inner ear, which is crucial to both hearing and balance, is almost impenetrable, making it difficult to study or for drugs to enter.

“It’s a teeny organ encased in a really, really hard bone,” said Dr. Hinrich Staecker, professor of otolaryngology at the University of Kansas School of Medicine. “The whole inner ear fits inside the tip of your pinkie.”

Executives at the new companies say that genetic and animal studies are revealing more about how the ear works. They note that the pharmaceutical industry once also neglected the back of the eye. Now there are blockbuster drugs like Genentech’s Lucentis and Regeneron’s Eylea that are injected into the eye to stave off blindness from retinal diseases.

The ear, they say, is the new eye.

Crucial to hearing are about 15,000 so-called hair cells in the cochlea, part of the inner ear, which convey signals to the auditory nerve leading to the brain. The hair cells can be damaged by loud noise, by disease, by exposure to certain medicines, or simply by the passage of time. And the hair cells do not regenerate, so once they are destroyed the loss is permanent.

But maybe not for Rob Gerk, a 31-year-old man in Denver who lost most of his hearing when he had meningitis as a toddler. He is the first patient in a clinical trial of gene therapy aimed at regenerating hair cells. The trial is being sponsored by Novartis and uses a gene therapy developed by GenVec, a Maryland biotech company.

In late October, Mr. Gerk underwent surgery by Dr. Staecker at the University of Kansas to infuse viruses carrying a gene called Atoh1 into his right inner ear. Atoh1 causes cells in a fetus to become hair cells. It is hoped that some of the supporting cells in the inner ear will take up the gene and turn into hair cells.