Cataracts are a clouding of the lens in the eye that affects vision. This fogging up of the eye's lens is most often the result of aging. By age 80, more than half of all Americans either have a cataract or have had cataract surgery.

The eye's lens is made of mostly water and protein and lies behind the iris and the pupil. The protein in the lens is arranged in a precise way that keeps the lens clear and lets light pass through it. But as we age, some of the protein may clump together and start to cloud a small area of the lens. This is a cataract. Over time, the cataract may grow larger and cloud more of the lens, making it harder to see.

Now, an eye drop that prevents cataracts from forming has been developed. The eye drops appear to work by preventing unwanted oxidation in the eye, especially in the lens. While they're not yet ready to be tested in humans, they've given some very impressive results in rats, cutting cataract formation by 80%.

The active ingredient in the eye drops is a chemical called NACA--n-acetylcysteine amide. It's a major improvement over a similar experimental drug n-acetylcysteine (NAC) because NACA is uncharged, allowing it to be taken up by cells more easily and requiring lower doses than a charged compound like NAC does.

Joshua Carey, a doctoral student at Missouri University of Science and Technology, tested the ability of NACA to prevent cataract formation in rats that were treated with BSO, a compound that causes cataracts to form, presumably by lowering levels of glutathione, a cell's major antioxidant. All rats given BSO formed cataracts. But when NACA was given to the rats 30 minutes prior to BSO, only 20% of the rats developed cataracts; the lenses of the other 80% remained clear. Carey also showed that NACA reversed the decrease in glutathione that occurred from BSO treatment.

Further animal testing still needs to be done to establish a proper dosage and frequency and to test for side effects before the drops can be tested in humans. Nuran Ercal, the principal investigator who Carey worked under, has recently received a three-year research grant from the NIH's National Eye Institute to begin answering these questions and also to see if NACA can reverse lens degeneration once a cataract has begun to form.

Currently, surgery is the only effective treatment for cataracts.

Vision loss from eye-related disorders affects more than 30 million people in the United States and is expected to double in the coming decades. As is true for cataracts, unwanted oxidation appears to play a role in macular degeneration, another common age-related eye disorder. Yet dietary antioxidant supplements don't seem to be effective at preventing or treating either condition. Perhaps introducing antioxidants directly into the eye, as the NACA eye drops do, will prove more effective.

Nuran Ercal, M.D. Ph.D., is Chair of Biochemistry at Missouri University of Science and Technology. She is also Adjunct Professor of Internal Medicine at St. Louis University and Professor in the Department of Chemistry at the University of Missouri-Rolla.