Crashing Through by Robert Kurson Page A

none had attempted it.
    • If successful, it could restore vision to the blind—even to those who had been assured they would never see.

    May briefed Jennifer on his discoveries. It felt strange to him to think about vision—he could remember doing it only once before. In his late twenties, he’d heard a man on the radio describe using hypnosis to help people recover childhood memories, and he’d wondered if a hypnotist might make him see what he’d seen before his accident. It was a fascinating proposition and one he’d entertained for a few days before returning to his busy life.
    “The stem cell surgery is really interesting,” he told Jennifer. “I’d like to know more about it. I still don’t think it would change my life, but I have to say, it seems like it’s for real.”
             
    V ision begins at the cornea. When light enters the eye, it passes first through the cornea, a transparent, circular layer one-fiftieth of an inch thick at the very front of the eye. The cornea has no color, but its job is critical—to allow light in and do the majority of focusing. The cornea must stay clear; otherwise, trying to see would be like trying to look through a frosted shower door or a dirty car windshield.
    But how are corneas kept clear? People can’t run wiper blades over them as with car windshields. The body, it turns out, has its own ingenious method for keeping the corneas clear. It begins with special cells known as corneal epithelial stem cells. These are not the controversial stem cells taken from embryos or fetuses, but rather cells that exist in every person for a lifetime.
    These stem cells reside along the edges of the cornea. If you imagine the cornea as a round window, the stem cells—about a thousand of them—live along the area where the frame would be. The stem cells produce millions of daughter cells. These daughter cells have a single mission: to converge toward the center of the eye, covering the cornea in a transparent protective layer.
    This protective layer of daughter cells is the cornea’s main defense against dirt, scratches, bacteria, and infection. It also prevents blood vessels and cells from the white part of the eye (known as the conjunctiva) from growing over the cornea. The protective layer itself might get dirty, but every few days the daughter cells that compose it fall off and are replaced by new ones, thereby ensuring perpetual freshness and clarity. The stem cells around the edges of the cornea never tire of making new daughter cells—they do it for as long as the person lives.
    But what happens if these stem cells are destroyed—perhaps by disease or burn or trauma to the eye? In that case, they can no longer produce the daughter cells that form the protective layer over the cornea. Soon, blood vessels and conjunctiva cells grow over the cornea, clouding it and then making it opaque. Light is no longer able to pass through the cornea on the way to the pupil, iris, lens, and retina. That means the person is blind. A chemical explosion—like the one that happened to Mike May when he was three—can destroy corneal epithelial stem cells instantly.
    Before 1964, scientists had little idea that the edges of the cornea play a role in keeping the cornea clear. And they certainly didn’t know of the existence of corneal epithelial stem cells and how they protect the cornea. When surgeons encountered a grown-over cornea, they removed it and transplanted a clear donor cornea in its place. That worked most of the time, because the patient still had stem cells around the edges capable of producing protective daughter cells. It failed, however, in cases when the patient lacked those stem cells. Ophthalmologists believed those failures to be caused by the body rejecting the donor cornea. They never suspected that the patient’s lack of stem cells was the cause of the donor cornea going bad.
    In 1964, a Colombian ophthalmologist named José Barraquer treated one of his