DLS was originally developed to study protein crystal formation on the International Space Station (ISS), with the goal of exploring possible new drugs. "In space, due to the lack of gravity, you are able to do a better job of growing better-quality and bigger crystals," says Rafat Ansari, a senior scientist at NASA's John H. Glenn Research Center, in Cleveland. When Ansari's father developed cataracts and the NASA researcher learned the role that protein changes play in their formation, Ansari began to explore the use of DLS as a means of earlier detection.

Laser light is shone into the lens of the eye while a highly sensitive photon detector called an avalanche photodiode is used to measure light backscattered at specific wavelengths. Because alpha-crystallin proteins are much smaller than the proteins that make up cataracts, they move differently. "Brownian motion is effectively controlled by the size of the particles," says Ansari, so smaller particles will move faster than larger ones.

By tuning the photon detector to monitor specific wavelengths over a period of about five seconds, it is possible to accurately measure alpha-crystallin levels.

"Alpha-crystallins are a reliable biomarker for cataracts and demonstrating this in humans is an advance," says Krishna Sharma a professor of ophthalmology at the Mason Eye Institute in Columbia, MO. The process is tricky, Sharma says, because pigments within the lens can affect the visible light scattering back.

The device has so far been tested in a clinical trial involving 235 patients. "We had a whole range, from young people with perfectly clear lenses to older people," says Datiles. The results were recently published in the journal Archives of Ophthalmology. "We were surprised that we can detect the alpha-crystallin proteins in a clear lens even before a cataract has appeared," he says.

The group is now working on a longer-term National Institute of Health study to monitor alpha-crystallin levels in patients with existing cataracts. The hope is that the technique will eventually prevent cataracts from forming in the first place. "Our hope is that millions of people will benefit from this," says Datiles.