For centuries, the phrase "to bring eyesight to the blind" was shorthand for a miracle--something that couldn't be done. But times have changed. With new techniques involving stem cells, gene therapy, and tiny electronics, researchers are getting ready to perform that medical miracle.
A TINY TELESCOPE FOR YOUR EYE
If you think about it, the lens in your eye is nothing more than a mini-telescope that lacks the ability to magnify images. So why not replace it with the real deal? That's a proposition that the optics company VisionCare Ophthalmic Technologies wants sufferers of end-stage macular degeneration to consider.
Macular degeneration gradually diminishes vision by damaging the macula, an oval-shaped yellow spot located in the center of the retina. That reduces people's ability to see anything directly in front of them. VisionCare's tiny implantable telescope (only 3.6 millimeters in diameter) replaces the patient's lens and squeezes as much performance as possible out of the few remaining healthy areas of the retina by focusing a wider angle of light and images onto the perimacular cells, rather than the central macula.
Working in conjunction with the cornea, the effect of the telescope is to magnify images in front of the eye roughly 2.2 to 2.7 times their normal size. In a recent clinical trial on patients aged 75 and older, 90 percent of the 219 participants were able to read two lines or more on an eye chart, and 75 percent could read large-print books.
All male squirrel monkeys are color-blind. Unlike their better-endowed female counterparts, these fellows lack a crucial visual pigment called L-opsin that let them distinguish reds from greens. For two lucky male squirrel monkeys, however, color-blindness is now a thing of the past. Reasoning that the female version of L-opsin might also do the trick for males, researchers from the University of Washington used a harmless virus to carry the pigment gene behind the monkeys' retinas.
The adult monkeys, nicknamed Dalton and Sam, had already been trained to recognize specific patterns of blue and yellow dots against a gray screen; now the scientists checked to see if they could also see patterns of red and green dots. Success came about 5 months later, when the duo began paying attention to the new colors. It's now been two years since the monkeys first experienced the full color spectrum, and there have been no further changes in their vision and no noticeable side effects. Researchers hope this technique will lead to treatments for color blindness in humans.
Firecrackers, acids, even exploding eggs--these are some of the known hazards that have resulted in burned corneas. If only slightly scratched, the cornea is more than capable of patching itself up by replacing the damaged cells with new ones from the limbus, a ring that encircles the iris. A burn or a deeper injury wreaks havoc on the limbus, however, forcing the eye to heal itself by taking cells from the white of the eyeball, clouding the cornea in a milky haze.
A treatment developed by Italian scientists could provide lasting relief to these beleaguered victims. For the procedure, which was first performed in 1995, the team harvested the same limbal stem cells that the cornea uses to fix itself and cultivated them on contact lens-like sheets. They then grafted them onto the patients' corneas. The procedure was a striking success. It fully restored the vision of 82 of 117 eyes with scorched corneas (although some needed more than one graft), and partially restored that of 14 others.
The German company Retina Implant AG has developed an implantable microchip that's installed directly under the retina, which stimulates intact inner nerve cells to produce artificial vision. The chip measures 9 millimeters long and wide, and is only 0.1 millimeters thick. Around 1,500 light-sensitive photodiodes, amplifiers, and electrodes in the chip absorb light and convert it into the electricity that activates the nerve cells. A series of transmitter coils buried under the skin behind the ear power the chip. One of its main advantages is the lack of external components, such as the tiny video cameras and transmitters that are used in most epiretinal (over the retina) approaches.
The 11 patients who participated in Retina Implant's first clinical trial, which began in 2005, saw marked improvements in their abilities to read and recognize objects and outlines. Initially all that the chip-assisted eyes can detect are lines, but the brain quickly learns how to piece them together in order to recognize words and images. A more recent study from Retina Implant showed even greater promise, with videos showing one previously blind patient who could identify apples and bananas, and who could tell when his name had been misspelled.
Over 10 million older Americans suffer from macular degeneration, in which the retina's central macula gradually breaks down. Researchers still haven't found an effective way to stanch this deterioration. But a few months ago a team of UC Irvine researchers discovered a way to circumvent this vexing dilemma: just grow a new retina.
In the study, scientists coaxed stem cells into forming a fully three-dimensional tissue structure. They got the embryonic stem cells to differentiate into all the different retinal precursor cells (the gorgeously stained cells in the picture above) by bathing them in specially prepared solutions meant to mimic their natural environment. After testing the technique on animals to see if it can at least partially restore sight, the researchers hope to create lab-grown, transplantable retinas that could be used to treat the millions who suffer from eye disease.
In a long-awaited success for gene therapy, a research team from the University of Pennsylvania restored sight to two patients suffering from Leber's Congenital Amaurosis (LCA), a previously untreatable form of blindness. The patients had malfunctioning RPE65 genes, which code for a protein that ensures the photoreceptor cells in the retina work smoothly. The scientists used a harmless virus to shuttle a healthy version of the gene into their eyes. As early as a week after the injection, the patients began showing noticeable signs of improvement as the proteins began to have their intended effect on the patients' few remaining photoreceptor cells.
The improvements lasted well after the study's conclusion three months later. The researchers had initially planned on keeping the results confidential--the trial was only designed to test the procedure's safety--but they were so impressed by the results that they decided to share them with the rest of the world. This image shows, at left, an LCA patient's eye before treatment, with a healthy eye at right for comparison.
If you need more incentive to indulge in a glass of wine, here's more good news about the health benefits of resveratrol, a chemical compound found in grapes and some other foods. Studies suggest that resveratrol could not only fight obesity's health effects and slow the aging process (albeit only in animals like mice and fish so far), the chemical may also hinder the abnormal growth of blood vessels behind the retina--the prime cause of macular degeneration. This high-magnification image shows a retinal hemorrhage in a patient with macular degeneration.
After reading about resveratrol's beneficial effects in other parts of the body, Rajendra Apte, an ophthalmologist from Washington University at St. Louis, decided to probe its efficacy in the eye. The effects were rapid and pronounced in mice that suffered from runaway blood vessel growth. Shortly after they were given the resveratrol, their extra blood vessels began to vanish and no new ones formed. But before you go running for the nearest bottle of merlot, keep in mind that the mice received the resveratrol equivalent of several bottles of wine.
Beatrice de Gelder couldn't believe her eyes. How could "TN," a patient who had been blinded by two strokes that destroyed his visual cortex, be weaving his way so masterfully through the obstacle course that she and her colleagues had erected? Though unable to see in the literal sense of the word--he had consistently failed all the vision tests that de Gelder had given him--he somehow "saw" the office supplies scattered in front of him and avoided them.
The researchers concluded that TN possessed a rare form of "blindsight" wherein a brain-damaged person with normal eyes can't process visual information but can still subconsciously react to it. They reason that previously suppressed neural pathways located below TN's destroyed cortex may be stepping in to fill its role, albeit on a subconscious level.
Though it may not be possible to fully restore their sight, blindsight patients can recover some of their vision by exercising other regions of the brain involved in motor perception. In a separate study, researchers from the University of Rochester found that stroke patients who "honed" their blindsight through a series of eye exercises over several months were able to recoup some of their former abilities.
