Cataracts are the single biggest cause of blindness and are responsible for almost half of all cases worldwide. A new laser probe, originally developed for the U.S. space program, has been shown to detect the condition earlier than is otherwise possible. Its developers say that the technique can tell that a cataract is forming even when an eye looks perfectly clear.

Cataracts are caused by the buildup of damaged proteins within the eye's lens, clouding it over and impairing vision. "The proteins start to unravel when they are damaged, and stick together to form clumps," says Manuel Datiles, a medical officer and senior clinical investigator at the National Eye Institute, in Bethesda, MD, who has been assessing the new technique.

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, contribute to the problem. Once cataracts have developed, the most common treatment is replacing the impaired lens with an artificial one. But if cataracts can be detected early enough, then it may be possible to slow or stop the accumulation of damaged proteins by reducing relevant factors, says Datiles.

Normally, diagnosis is carried out by looking for protein buildup in the eye with a slit-lamp microscope--a standard ophthalmological device that illuminates the eye with a beam of light so that it can be examined with a microscope. However, slit-lamp microscopes can only detect cataracts once they have formed, Datiles says. "This new method detects cataracts even before they can be detected normally, and before they are symptomatic," he notes.

The new technique uses dynamic light scattering (DLS) to detect small proteins called alpha crystallins in the eye's lens. These are known to play a natural role in preventing cataracts from forming by sticking to larger proteins and stopping them from unraveling. If the larger proteins cannot unravel, then they cannot stick together.

Cataracts can still form because there are only a finite number of these proteins in the eye, and they are gradually depleted. So these alpha crystallins can be a useful biomarker, Datiles says: "If the amount of alpha-crystallin proteins has dwindled, then you know something is happening."

Alpha-crystallin proteins are between one and three nanometers in diameter--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.