To get a better look at the abnormalities that cause age-related macular degeneration, the leading cause of vision loss in Americans and Europeans over 50, researchers have created ultra-detailed 3-D images of the eyes of more than 2,000 people from different ethnic groups, 400 of whom have macular degeneration.

Macular degeneration is a condition in which the macula, the region of highest visual acuity in the retina, stops functioning properly. Macular degeneration causes blurred vision and, in advanced cases, a large blind spot in the center of one's vision.

Optical coherence tomography (OCT) has become a standard tool for assessing macular degeneration and other eye diseases. An OCT instrument shoots beams of infrared light into the retina, where they are reflected to greater or lesser extent by different structures within the eye. By measuring the echo time delays of reflected light, an ophthalmologist can have a cross-sectional or three-dimensional view of the retina's layers. This high-resolution, three-dimensional image reveals abnormalities that can be used to track disease progression and response to treatment.

Researcher Fujimoto and his team use an OCT machine with a resolution two times higher than commercial OCTs. In this study, they imaged the retinas of 400 people suffering from different stages of macular degeneration. Their profiles range from a 54-year-old man with mild macular degeneration and 20/20 vision, to a 77-year-old woman with advanced macular degeneration who can just barely count fingers from a distance of four feet. Each person's eye was scanned in 180 different slices and stitched together to form a 3-D image of the eye.

Most of the patients suffer from "dry" macular degeneration, the milder and more common form of the disease. The hallmark of this condition is drusens, small yellowish clumps that build up between the layers of retina. These masses tend to progress with time, eventually disrupting the structure of the retina.

Ultra-high resolution OCT reveals the detailed structure of these changes with a resolution that enables individual layers of the retina to be visualized. "This would be hard to resolve with the standard resolution of a typical commercially available OCT instrument, which cannot see ultra-thin layers," says co-author Yueli Chen.

Scans of other patients' eyes show a more advanced "wet" form of macular degeneration, in which abnormal blood vessels grow in between the layers of the retina. 3-D OCT provides a more accurate estimate of the volume of fluids leaked by these faulty vessels, which damages the photoreceptors in the eye and leads to blindness.

The electronic data in these 3-D images is being published in order to make it available to the image processing community to develop computer programs that can quickly and automatically detect the details and severity of the disease, by counting the number of drusens, for example, or quantifying the volume of fluid leaked into the eye by faulty blood vessels. Developing these programs will be difficult because of the sheer quantity of data contained in each data set says Fujimoto, but it is important because quantitative measurements can be used to track disease progression and help establish correlations between the severity of vision loss and changes in the architecture of the eye.

Researchers say this could provide a faster and more efficient way to develop and evaluate new treatments in clinical trials. No treatment currently exists for dry macular degeneration, and treatments for the wet form, including lasers that burn the blood vessels can only slow, not stop, vision loss.

Increasing the consumption of foods rich in certain carotenoids, in particular dark green, leafy vegetables, may decrease the risk of macular degeneration.

Observational and clinical trials support the safety of higher intakes of the phytochemicals lutein and zeaxanthin and their association with reducing risks of cataracts in healthy postmenopausal women and improving clinical features of macular degeneration in patients.
References:
1. Yueli Chen et al, Three-dimensional ultrahigh resolution optical coherence tomography imaging of age-related macular degeneration. Optics Express, Vol. 17 Issue 5, pp.4046-60.
2. Rhone M, Basu A. Phytochemicals and age-related eye diseases. Nutr Rev. 2008 Aug;66(8):465-72. PMID: 18667008.
3. Seddon JM, Ajani UA, Sperduto RD, Hiller R, Blair N, Burton TC, Farber MD, Gragoudas ES, Haller J, Miller DT, et al. Dietary carotenoids, vitamins A, C, and E, and advanced age-related macular degeneration. Eye Disease Case-Control Study Group. JAMA. 1994 Nov 9;272(18):1413-20. PMID: 7933422.
4. Image by Patrick J. Lynch, medical illustrator; C. Carl Jaffe, MD, cardiologist.