A keen view of vision: seeing cone cells.

At the back of an eye lies the retina, a tissue-paper-like membrane studded with rod and cone cells. Those cells facilitate sight by transforming light energy into electrical signals, which are then sent to the brain. Yet seeing those cells in action is difficult. While scientists study retinal cells removed from eyes donated for research, they have been unable to watch single vision cells at work in living subjects.

Now, Donald Miller, David Williams, and G. Michael Morris, all researchers at the University of Rochester (N.Y.), have brought astronomical technology to bear on the retina. Using lasers and charged coupled devices (CCDs) originally designed for stargazing and military applications, they have observed individual, live cone cells with a resolution as small as 3 micrometers, they said this week at a meeting of the Optical Society of America in Dallas.

"This resolution is three times greater than the resolution that people have attained so far," says Williams. "It's the highest resolution of photoreceptors in living retinas for an image taken outside the eye. This offers a new benchmark for how fine a structure one can see in living retinal tissues. And we're hoping to see more detail in blood vessels, receptors, and other types of eye cells."

To obtain such images, the researchers use an argon laser to bounce a quick flash of light off the retina. They then capture the reflected beam with a CCD, which funnels the signal into a computer for processing and display. The patient remains awake the whole time.

To improve the instrument's acuity, Williams and his colleagues will incorporate an "adaptive optics" system used by astronomers to help compensate for atmospheric disturbances when viewing light from distant stars. This system has effectively compensated for the optical distortions that arise within an eyeball and obscure a high-resolution view of the retinal cells.

Williams sees two potential uses for this imaging method. One is to help physicians diagnose and chart the course of certain eye diseases -- such as macular degeneration or retinitis pigmentosa -- before disabling symptoms appear. The second possible use is scientific. "We don't yet understand very well how light is absorbed into the pigments of photoreceptors," Williams says. "Maybe by looking at these receptors we can gain some insight into how light passes through the retina's photore-ceptive layer."