Macular degeneration, an eye disease that affects more than 13 million Americans, is the leading cause of blindness in people older than 65 in the USA. A test developed by University of Utah ophthalmology and physics researchers could help physicians detect the onset of age-related macular degeneration (AMD) and monitor the effects of nutritional intervention. Designed for the noninvasive in vivo measurement of carotenoid antioxidant molecules in human tissue, the test also may be able to gauge a patient's susceptibility to skin cancer.
Carotenoids Protect Eyes
Using low-energy resonance Raman laser spectroscopy, the test measures the levels of two macular carotenoid pigments called lutein and zeaxanthin, according to Paul S. Bernstein, M.D., Ph.D., assistant professor of ophthalmology and visual sciences at the University of Utah's Moran Eye Center, and Werner Gellermann, Ph.D., research professor in the University of Utah's department of physics and associate director of the university's Dixon Laser Institute. Found in dark-green leafy vegetables, such as spinach and broccoli, and yellow- and orange-colored fruits and vegetables, such as peaches and corn, these pigments are said to protect the eye from light-induced oxidative damage and aging. They are found in such abundance in the human macula that they color it yellow, Bernstein says.
Diet and Nutrition Affect AMD
"Lutein and zeaxanthin are potent antioxidants that absorb the blue region of the visible spectrum, the most damaging wavelengths of light for the retina," explains Bernstein. "This new test will allow us to determine whether raising a patient's macular pigment levels through diet and nutritional supplements translates into a lower risk for macular degeneration."
The noninvasive test requires the patient to look into a light for just 1 s. The light is slightly absorbed by the eye and then scattered or reflected back to the equipment. The reflected light can be analyzed for a variety of carotenoids, including lutein and zeaxanthin, because they each have a very specific "signature," originating from vibrations within their molecular structure. Clinical trials of this new technique have involved several hundred patients and several prototype instruments. Ultimately the test could become as common as tests for intraocular pressure and visual fields used to assess the risk for glaucoma, according to Bernstein.
Raman spectroscopy is usually considered unsuitable for routine measurements in living tissue, according to Gellermann. Because Raman signals are typically of weak intensity, the researchers needed to use lasers in combination with sophisticated light collection and analysis instrumentation. Macular pigments glow green, exhibiting extremely strong Raman signals when a blue laser light shines on them. Under proper conditions, this resonance amplification can be as high as a factor of 10,000, turning a weak signal into a readily measured strong signal many times higher than background signals from other cells in the retina. Then the retina can be exposed to light levels that are within established safety ranges. Bernstein says the new technique also can be used with higher reliability than heterochromatic flicker photometry, the most commonly used test to measure macular pigments, in patients with significant visual loss from macular degeneration or other diseases.
In the skin, important antioxidant molecules include the carotenoids lycopene and various carotene isomers, Bernstein says. Although the carotenoid levels in the skin are approximately two orders of magnitude lower than in the macula and although there is a large native fluorescence level in the skin, the technique can measure carotenoid levels over a large concentration range. In addition, it is possible to monitor changes in skin carotenoid levels as a result of dietary intervention based on the test results.
To Reach Market in 2003
The University of Utah researchers have received a US patent on the Raman spectroscopy device. Bernstein and Gellermann initially received funding for their research from the State of Utah Centers of Excellence Program. Recently the researchers obtained a $500,000 Small Business Technology Transfer grant from the National Institutes of Health and the National Eye Institute. They have also formed a start-up company Spectrotek to develop the device for routine testing in eye clinics. Based on the results of their current clinical study, the researchers predict that the device could reach the market by 2003.
Source: Medical Laser Report, July 2001