A laser probe originally developed for the U.S. space program has been shown to detect cataracts earlier than is otherwise possible. Developers say the technique can spot forming cataracts even when eyes look perfectly clear.

Cataracts are the buildup of damaged proteins within the eye's lens, clouding it over and impairing vision. “Damaged proteins start to unravel and clump together,” says Manual Datiles, a medical officer and senior clinical investigator at the National Eye Institute in Bethesda, Maryland.

When using the probe, laser light is shone into the lens of the eye while a sensitive photon detector, an avalanche photodiode, measures specific wavelengths of backscattered light. Because alpha-crystalline proteins are smaller than proteins that make up cataracts, they move differently. “Brownian motion is effectively controlled by the particle size,” says Rafat Ansari, a senior scientist at Nasa's John Glenn Research Center, Cleveland. So smaller particles move faster than larger ones. By tuning the photon detector to monitor specific wavelengths over a period of about five seconds, it can accurately measure alpha-crystalline levels. These play a natural role in preventing cataracts from forming because they stick to larger proteins and stop them from unraveling and clumping.

A common treatment replaces the impaired lens with an artificial one. Datiles says detecting cataracts early enough may make it possible to slow or stop accumulation of damaged proteins by reducing relevant factors. The protein buildup that causes cataracts can be triggered by age, but various stress factors, such as exposure to cigarette smoke and poor blood-sugar management in diabetics also contribute.

Conventional diagnosis looks for protein in the eye with a slit-lamp microscope, a standard ophthalmologic device that illuminates the eye so it can be examined with a microscope. However, says Ditalies, this only detects cataracts after they form. “The new method finds cataracts even before they can be detected normally, and before they are symptomatic,” he says.

Cataracts form because there are a finite number of alpha crystalline in the eye and they gradually deplete. So the crystalline can be a biomarker. “If the amount of alpha-crystalline proteins dwindles, something is happening.” Alpha-crystalline proteins are 1 to 3-nm dia., too small to detect using conventional equipment. But DLS can spot them by measuring the way that light is reflected by particles in a liquid.

DLS was originally developed to study protein crystal formation on the International Space Station with the goal of exploring possible new drugs. When the father of developed cataracts, the NASA researcher learned the role that protein changes play in their formation and began exploring use of DLS as a means of earlier detection.

The device has been tested in a clinical trial of 235 patients. “We were surprised to detect the alpha-crystalline proteins in a clear lens even before a cataract has appeared,” says Datiles.