I Spy With My Eagle Eye

The quest for super-vision.

Optics, defined

Super-vision is the indispensable comic-book power. Superman sported X-ray sight. Other superheroes were gifted with night vision, eagle eyes, or even eyes that fired deadly laser beams (a kind of Lasik surgery, whacked inside out).

The eye is an obvious target for enhancement: Vision is our dominant sense, and the structure and function of the eye are relatively well-understood. From eyeglasses to contact lenses to cataract removal to laser surgery, there is a long history of tinkering with vision. And because so many people suffer from vision ailments (blindness, colorblindness, etc.), eye research is lavishly funded. Some of that research on damaged eyes may end up improving normal vision.

There are three ways this is likely to happen. The first is an easy-to-use technology that will soon be available. The second is a complicated technology that probably won’t be available for a decade or more. The third is a bizarre gene therapy that would be most remarkable of all, if anyone can figure out how to make it work.

1) Laser-Perfected Vision

The Background
Laser refractive surgery on the eyes—the most common technique is known as Lasik—has become one of the first mass-market operations, performed assembly-line-style at surgical factories around the country. Doctors cut away layers of corneal cells with laser beams. This reshapes the cornea, allowing it to focus light more correctly on the retina in the back of the eye.

But today’s Lasik is a relatively crude tool. It can correct most near- and farsightedness pretty well, and it can get rid of astigmatisms, but surgeons are stymied by what are called “higher-order aberrations.” These include the “spherical aberration”—in which a star looks like it has a halo—and the “coma”—in which a point of light looks like a streak. Higher-order aberrations, which affect most of us to some degree and one-third of people severely, blur and distort vision, especially at night. Until now, higher-order aberrations have gone uncorrected because no tool existed to detect them, much less fix them.

The Project
This is where Dr. David Williams comes in. Williams, a voluble 49-year-old who directs the Center for Visual Science at the University of Rochester, is the world expert on the structure and function of the eye. (When other eye scientists didn’t know the answer to a question I asked, they inevitably told me, “Call David Williams.”)

Williams is pioneering the use of an instrument called a “wavefront sensor” that can detect all distortions, from major nearsightedness to the tiniest coma. (This technique was first demonstrated by a former postdoc of Williams, Jinzhong Liang, when he was a grad student in Germany.) Borrowing from a field of astronomy called “adaptive optics,” Williams shoots light into the eye, then observes how it bounces back through 221 lenslets in the wavefront sensor. The patterns created by the lenses indicate all the aberrations of the eye. It is a kind of map of the eye’s mistakes.

Williams has proved that these errors can be fixed. In his lab, he has subjects stare at a deformable mirror that corrects the aberrations revealed by the wavefront sensor. When someone looks at this mirror, her vision is essentially perfect: All light is striking the retina exactly where it should. (The mirrors are not any kind of permanent solution, just an experimental technique for showing how to rectify errors.)

When people try his mirrors in the lab, Williams can cut their higher-order aberrations by a factor of 10 or 20, giving them sharper vision, especially night vision. At their best, Williams’ mirrors can correct vision to 20/10, the limit of normal human sight. (This limit is established by the density of cones and rods in the “fovea,” the heart of the retina. That density, combined with certain optical laws, means that human vision can’t get better than about 20/10 or 20/8. An eagle sees more sharply than we can because it has better optics and more densely packed cones.)

Williams’ adaptive optics system may eventually replace the phoropter, the device used by eye doctors to prescribe glasses and contact lenses. It is also being used to provide ultra-high resolution pictures of the retina, which will help in diagnosing and treating eye disease.

But adaptive optics will be most useful when it can be used to correct vision permanently outside the lab. That’s why eye surgeons are so interested in Williams’ work. His technique is fairly easily translated to surgery (and may also work for contact lenses). A laser surgeon can follow the map of errors revealed by the wavefront sensor, making minuscule, precise corrections on the corneal surface. No longer will laser surgery be limited to the big aberrations that surgeons can now eliminate: It could erase every error in the eye.

Williams is collaborating with Dr. Scott MacRae, a celebrated University of Rochester eye surgeon, who recently finished a laser surgery trial on more than 300 patients using the wavefront sensor. MacRae and Williams are also working with Bausch & Lomb to develop contact lenses that would eliminate higher-order aberrations. At a January conference, MacRae reported that 91.5 percent of the eyes treated in his study attained 20/20 or better vision six months after the surgery. And in another surgical trial of 340 patients, Dr. Stephen Slade reported that more than 70 percent achieved 20/16 vision or better.

The Obstacles
Even if the surgery proves to be a successful technique, it’s unrealistic to expect every patient to achieve 20/10 vision with no higher-order aberrations: Surgery is always risky, patients respond differently to treatment, and many have other visual problems that could weaken their sight.

Bausch & Lomb and its competitors are puzzling out how to apply wavefront sensor technology to contact lenses, which float around on the eye. To eradicate higher-order aberrations, the lenses must lock in one place—which remains an engineering challenge. MacRae says that Bausch & Lomb “is making inroads” on the customized contact lenses.

The Timeline
Neither Williams nor McRae would predict when such surgery or contact lenses might be used widely, but it will probably happen a few years from now, not a few decades. In November 2002, the FDA recently approved its first wavefront-guided surgical system, LADAR-Vision, which is made by Alcon, Bausch & Lomb’s competitor.

An eye into the eye

2) The Cyborg Eye

The Background
A dozen teams of American scientists are working on implants to restore sight to the blind. The scientists all begin with the same basic notion: Sight is essentially an electrochemical signal in the brain, and in the blind, something prevents the light that enters the eye from becoming a usable signal. (Usually, the source of this failure is the retina’s rods and cones, the delicate cells that detect light and color.) These implant scientists want to circumvent the broken parts of the eye and send a signal to the cells that still work.

The implant researchers take two basic approaches. Some want to place miniature light-sensitive photo arrays in the retina itself. This “retinal implant” replaces broken rods and cones. When light strikes the photo array, its sensors transform the light into an electrical pulse that fires the optic nerve, which in turn stimulates the visual field in the brain. Due to the difficulty of transmitting signals from machine to cell, today’s implants contain no more than 1,000 photoreceptors. The fovea, by contrast, has more than 100,000 rods and cones, meaning current implants might provide only a blurry, low-definition approximation of normal vision. (So far, only one outfit, a company called Optobionics, claims to have put a working implant in a human eye.)

Other groups are targeting the brain, not the eye. Rather than repair or implant eyes, they mount a camera on the head of the patient or build it into a pair of glasses. This camera transmits a picture to electrodes that have been implanted in the brain’s visual center or to the optic nerve. William Dobelle, a New York scientist, has just installed the first successful brain implant. He put electrodes—about 100 of them, according to a Wired reporter who witnessed the experiment—in a man who’d been blind for 20 years, then hooked the electrodes up to a signal processor and a camera. The blind man was able to see—very crudely, to be sure, but enough to walk around unguided. Dobelle’s implants suffer from the same shortcoming as retinal implants: With only 100-odd electrodes, they deliver a fuzzy facsimile of normal sight.

The Project
Brain imaging and miniaturization are improving rapidly. It’s possible that Dobelle and others will figure out how to feed 1,000 electrodes, or even 100,000 electrodes, into the brain or build retinal arrays with 100,000 sensors.

This is when super-vision becomes possible. Thanks to the camera, there is scarcely any limit on what an implanted person could see. You could equip the camera with a telephoto or fisheye lens. The camera could swivel. It could receive infrared light (the light that you see in night-vision goggles). So an implantee could see in the dark, or see behind him, or zoom in on a particularly interesting corner of his visual field. (The model for all this, I say with embarrassment, is Star Trek: The Next Generation’s Geordi La Forge, the blind character who can “see” infrared and UV light through his special visor.)

Retinal implants, too, could serve as cyborg eyes, though they wouldn’t be as sophisticated since they depend on normal light. But you could make a retinal implant in which the sensors respond to a broader range of wavelengths than the human eye does—including infrared light.

The Obstacles
Today’s implants are crude: Multiplying a 1,000-receptor retinal photo array into a 100,000-receptor array is a daunting problem. Going from 100 brain electrodes to 100,000 is even more difficult.

It’s also an invasive process that involves having holes drilled in your head and thousands of wires snaked into your brain. This may be an acceptable risk for a blind person who is eager for newfound sight, but what person with normal vision would choose such a process merely to see in the dark? (Especially since you can mimic the benefits of implants with noninvasive tools such as infrared goggles.) The blind will be the only customers for implants until they become stupendously good.

The final obstacle is the brain itself. It takes a long time to learn to see, and there is no guarantee the brain can retrain itself to master zoom lenses and infrared vision. People with cataracts who regain their sight after surgery sometimes remain “blind” because their brain can’t process the new visual stimulus. Rochester’s Williams, for one, is unsure the brain is plastic enough to handle vast amounts of new visual information.

The Timeline
Implants that offer some sight to the blind may be available in a decade. Super-vision implants probably won’t arrive for at least two decades.

3) The Rainbow Eye

The Background
The most audacious supereye would improve us by altering our own genes.

We see colors well because we have “trichromatic” vision: The retina hosts three kinds of “photoreceptive” cones, each sensitive to different wavelengths of the visible light spectrum. The light that enters the eye fires these cones in different amounts, allowing us to see all colors from white to black. (We can’t see light at longer—infrared—or shorter—ultraviolet—wavelengths.) In many colorblind people, the third cone doesn’t work. The two functioning cones deliver a muddy, narrow band of colors and a much poorer sensory experience. (To get a sense of what “dichromats” see, watch this slide show.)

Many animals, including birds and fish, have four cones, not three. The fourth cone is usually receptive to ultraviolet light, meaning these animals see a whole range of light that we cannot.

The Project
Medical College of Wisconsin professor of cell biology Jay Neitz, whose expertise is color vision, recently started to wonder what would happen if humans, like birds, had a fourth cone. Neitz and his wife, Maureen Neitz, who is a professor of ophthalmology at MCW, are working with a species of monkey that has only two kinds of cones. The Neitzes have created a virus containing a gene for a photopigment that the monkeys do not have, and they’ll inject this virus into their eyes. If some of the cones absorb the viral DNA, the monkeys should become receptive to light of different wavelengths—the light that the new photopigment senses. The monkeys would then have three kinds of cones. If their brains are able to process the new information, the monkeys might leap from dichromatic vision to trichromatic vision.

If this experiment succeeds in monkeys—and assuming progress in human gene therapy, thus far mostly a failure—the Neitzes will try a similar technique on colorblind humans, attempting to give them a third, functioning cone. If that proves successful, the Neitzes hypothesize, you ought to be able to give people with normal sight a fourth cone, equipping us “tetrachromatic” vision.

What would tetrachromatic vision be like? Jay Neitz can only speculate based on the astounding difference between dichromatic and trichromatic vision. Because of the way the nervous system works, a fourth cone “would add two more entirely new colors, completely new and wonderful and unimaginable sensations. … And it is not just those two new colors but the combinations of those colors with all the colors we already see. We would see almost everything differently.”

There are weirder possibilities, too. In their first four-cone experiment, the Neitzes think they would engineer a photopigment sensitive in the visible light spectrum (probably in the gap between our current blue and green cones). But they could also make a cone receptive in the infrared zone. If the cones were to become too sensitive to infrared light, though, we would start “seeing” our own body heat, and that would blur our vision. But if you could engineer cones that were somewhat sensitive to the infrared spectrum, we might have extraordinary night vision—without goggles, street lights, or surgery.

The Obstacles
Most human gene therapy trials have been unsuccessful. Until scientists puzzle out how to make implanted viral genes stick and not bite back, gene therapy for the eyes will remain only a hope.

Even if the Neitzes can make the gene therapy work, the brain may rebel. As with the cyborg eye, no one is certain the brain would accept the signals of a fourth cone, although Jay Neitz believes the mind is plastic enough to accept the strange new sights.

The Timeline
The Neitzes are in the final stages of preparation for their initial monkey trial.