The quest for extraordinary vision.

The quest to build better people.
March 5 2003 6:41 PM

I Spy With My Eagle Eye

The quest for super-vision.

Optics, defined
Optics, defined
David Plotz David Plotz

David Plotz is Slate's editor at large. He's the author of The Genius Factory and Good Book.

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.)



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