Technology Takes New Look at Color Blindness

Astronomy tool used in optometry

MONDAY, May 17, 2004 (HealthDayNews) -- A technology originally developed for military space purposes has helped solve a puzzle about color blindness and holds promise for diagnosis and treatment of a number of eye disorders, new research says.

The technology is adaptive optics, which uses a constantly changing mirror to give clear pictures of images that would otherwise be blurred because they are passing through a constantly changing medium -- the earth's atmosphere in astronomy, the fluid of the eye in optometry.

Adaptive optics has become a powerful tool of ground-based astronomy. Its potential medical uses are illustrated by this latest report.

Researchers at the University of Rochester in New York, where much work on adaptive optics has been done, report in this week's issue of the Proceedings of the National Academy of Sciences that they have used the technology to compare the light-receiving molecules in the eyes of two color-blind individuals.

The eye has two kinds of light receptors -- cones, which are sensitive to light but not colors, and rods, which come in three varieties sensitive to red, blue and green.

"This is the first time we have been able to see rods and cones on a single-cell level," said study author Joseph Carroll, a postdoctoral fellow in the Rochester Center for Visual Science.

What they saw in one color-blind person was the normal number of cones, but all the red cones had been replaced by green cones. In the second individual, all the green cones were missing. Remarkably, this loss of one-third of all the cones did not reduce visual acuity.

"This person had no idea that there was anything wrong with his vision other than color blindness," Carroll said.

That finding has no immediate medical application, but Carroll said "it opens the door to the study of many more common retinal diseases that cause loss of vision." One such condition is retinitis pigmentosa, in which rods and cones begin to die in the peripheral part of the visual field, with the loss moving inward to eventually destroy central vision.

What is needed for medical use of adaptive optics is a low-cost mirror, Carroll says. An adaptive technology mirror now costs upwards of $100,000. The goal is to bring that down to about $1,000. Work toward that goal is part of the mission of the Center for Adaptive Optics, funded by the National Science Foundation, which includes 13 institutions across the country.

One of those Institutions is the University of Indiana School of Optometry. Donald T. Miller, an associate professor of optometry there, said "we are working to combine adaptive optics with other technologies to get a better view of the eye."

Adaptive optics gives an image of the surface of the retina, Miller said, but it cannot look into the three layers of cells that make up the retina.

"The push here is to combine adaptive optics with optical coherent tomography, which would give a direct indication of the health of the retina, particularly related to glaucoma," Miller said.

Glaucoma causes vision loss by steadily destroying retinal cells as pressure builds up in the eye. The condition can be treated with drugs that reduce pressure, but "the problem is that we have a difficult time diagnosing whether a patient has glaucoma, and so we tend to err on the conservative side," Miller said. Better images could prevent unnecessary use of drugs, he added.

For retinitis pigmentosa, "we need to be able to image rods and cones as well, and no one has been able to do that yet," he said. Recent reports indicate that adaptive optics may be able to achieve that goal, Miller said.

More information

An overview of the varied uses of this technology is given by the Center for Adaptive Optics. Go to MedlinePlus to find an example of a color blindness test.

SOURCES: Joseph Carroll, Ph.D., postdoctoral fellow, Center for Visual Science, University of Rochester, N.Y.; Donald T. Miller, Ph.D, associate professor, optometry, University of Indiana, Bloomington; May 17-21, 2004, Proceedings of the National Academy of Sciences
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