Science Daily

by American Chemical Society

    Millions of Americans live with vision problems ranging from mild blurriness to severe vision loss. Glasses and contact lenses can correct many common problems, but some people turn to surgery for a more permanent solution. Hundreds of thousands of Americans undergo corrective eye procedures each year, including LASIK, which uses a laser to reshape the cornea and improve how the eye focuses light.

    Now researchers are investigating a very different approach. Instead of cutting away corneal tissue with a laser, they are testing a technique that temporarily makes the cornea flexible enough to be reshaped.

    Early experiments using rabbit eye tissue suggest the method could potentially correct vision in about a minute, without incisions and with much simpler equipment than LASIK requires.

Why the Shape of the Cornea Matters

    The cornea is the clear, dome-shaped surface covering the front of the eye. It plays a major role in vision by bending incoming light so it can be focused onto the retina, the light-sensitive tissue at the back of the eye. The retina then converts that light into signals that the brain interprets as images.

    When the cornea does not have the right curvature, light may not focus properly. This can cause refractive errors such as myopia, better known as nearsightedness, in which distant objects appear blurry.

    LASIK corrects these problems by using specialized lasers to remove extremely precise amounts of corneal tissue and change its shape. The procedure is widely used and generally considered safe, but it still involves permanently removing tissue and can carry side effects and other risks.

    Michael Hill, a professor of chemistry at Occidental College, puts it more bluntly: "LASIK is just a fancy way of doing traditional surgery. It's still carving tissue -- it's just carving with a laser."

    That led researchers to consider a very different question: Could the cornea be reshaped without cutting it at all?

Reshaping the Eye With Electricity

    Hill and collaborator Brian Wong are studying a technique called electromechanical reshaping (EMR). Rather than physically removing tissue, EMR uses a small electric potential to temporarily alter the chemical environment inside the tissue.

"The whole effect was discovered by accident," explains Wong, a professor and surgeon at the University of California, Irvine. "I was looking at living tissues as moldable materials and discovered this whole process of chemical modification."

    The approach takes advantage of the chemistry that helps tissues maintain their shape.

    The cornea contains large amounts of collagen, a structural protein also found in skin, cartilage, tendons, and other tissues. Within collagen-rich tissue, electrically charged components attract one another and help hold the structure firmly in place.

    Because these tissues also contain a large amount of water, applying an electric potential can change their pH. The pH scale measures how acidic or basic something is. Lowering the pH makes the tissue more acidic and temporarily weakens some of the electrical attractions that keep its structure rigid.

    During that brief window, the tissue becomes easier to reshape. Once its normal pH returns, those interactions are restored and the tissue can remain in its new form.

    Researchers had previously used EMR to reshape cartilage-rich rabbit ears and to modify scars and skin in pigs. The cornea was an especially intriguing target because its precise curvature determines how effectively the eye focuses light.

A Platinum "Contact Lens" Molds the Cornea

    For the new experiments, the researchers built specialized platinum "contact lenses" designed to act as molds for the desired corneal shape.

    They placed the lenses over rabbit eyeballs immersed in a saline solution intended to mimic natural tears. Because platinum conducts electricity, the lens also functioned as an electrode. When a small electric potential was applied, it produced a carefully controlled change in pH inside the cornea.

    Within about a minute, the curvature of the cornea shifted to match the shape of the platinum lens.

    That is roughly comparable to the amount of time involved in the laser portion of LASIK, but the experimental EMR method required no incision and potentially could use simpler, less expensive equipment.

Early Tests Corrected Simulated Nearsightedness

    The researchers tested the method on 12 rabbit eyeballs. Ten were treated as though they had myopia, or nearsightedness.

    In every one of those "myopic" eyes, EMR changed the cornea enough to reach the intended focusing power. In practical terms, that type of optical change would be expected to improve vision if the same effect could eventually be reproduced safely in a living eye.

    Importantly, the cells in the treated eyes survived the procedure. The researchers achieved this by carefully controlling the pH gradient so the chemical changes were large enough to reshape the cornea without causing excessive damage.

    The experiments also hinted at another possible use.

    In separate tests, researchers found that EMR might be able to reverse some chemical-caused cloudiness to the cornea -- a condition that is currently only treatable through a complete corneal transplant.

    If that result holds up in future studies, the technique could potentially have applications beyond ordinary vision correction.

A Long Way From Replacing LASIK

    Despite the encouraging results, the researchers stress that EMR remains at a very early stage.

    So far, the vision-correction experiments have been performed on isolated rabbit eyeballs rather than living animals. The next major step is what Wong describes as, "the long march through animal studies that are detailed and precise," including testing the technique in a living rabbit.

    Researchers also need to determine exactly which types of refractive errors EMR could correct. Those could potentially include near- and far-sightedness and astigmatism, a common condition caused by an irregularly shaped cornea or lens.

    Many other questions would also need to be answered before the approach could ever be tested widely in people, including how stable the reshaping is over time and whether repeated or long-term effects emerge in living eyes.

    For now, progress has also been slowed by uncertainty surrounding the team's scientific funding.

    "There's a long road between what we've done and the clinic. But, if we get there, this technique is widely applicable, vastly cheaper and potentially even reversible," concludes Hill.

    This research was funded by the National Eye Institute of the National Institutes of Health and the John Stauffer Charitable Trust.