The discovery of a surprise lurking in the retinas of colorblind people may have ramifications for understanding a number of eye disorders. Using a technique called “adaptive optics,” which was originally developed to help astronomers see more clearly through the Earth’s atmosphere, researchers at the University of Rochester have discovered that as many as one-third of the light-detecting “cones” in a colorblind person’s eye can be missing, yet amazingly, visual acuity appears unaffected. The work is published in a recent issue of the Proceedings of the National Academy of Sciences.
“Not only are we excited to show how this method can reveal us living cells in a way never before possible, but it’s revealed a mystery with profound implications,” says Joseph Carroll, a postdoctoral fellow at the Center for Visual Science at the University of Rochester and lead author of the paper. “If a third of the light-receiving cells in your eye are absent and you don’t even notice it, it means that when a patient complains to a doctor about waning light sensitivity, then the damage must already be very serious.”
The findings were possible thanks to a laser-based system developed by David Williams, director of the University’s Center for Visual Science, and colleagues at the University over the last decade that maps out the topography of the inner eye in exquisite detail. The team built on technology known as adaptive optics, initially proposed by astronomer H. W. Babcock in 1953, then developed by the U.S. military to clear up images from spy satellites. The idea is to correct for aberrations in the atmosphere so that rays of light travel in parallel lines and converge at a single point, delivering a sharp image. Astronomers use the technique in telescopes to grab ever-better photos of the heavens. Williams leads the effort to apply the same technology to human vision.
The adaptive optics technique allows researchers to study the retina in ways that were never before possible. Being able to peer into the eye of a living patient affords a researcher to ask simple questions, like the most basic in this case—“Are you colorblind?” Many diseases degenerate the cells of the retina, and since donated tissue does not have a medical history attached, it’s very difficult to know whether a sample of tissue came from a colorblind individual or someone suffering from another malady.
The ability to work with live patients also gives the researchers access to further tests of their overall health, including behavioral and genetic tests which can help determine what kind of disease may be causing damage to their retina.
“The real lesson learned here is that adaptive optics becomes incredibly powerful when coupled with other technologies,” says Carroll. “When we combine it with retinal densitometry, for instance, we can determine the amount and kind of pigment in the retina at the cellular level. Our ability to understand the retina and diseases of the retina is going to see big advances as this technology is merged with others.”
Noting how useful adaptive optics can be in helping to spot and diagnose disease of the retina earlier than is possible with current clinical techniques, the researchers are working to build five new adaptive optics machines to be used around the world in vision clinics. The cost of the deformable mirror itself is the main stumbling block. At more than $100,000, it is prohibitively expensive, but Carroll and others at the Center for Adaptive Optics, which includes 11 institutions across the country, are working with industry partners to bring that cost down to below $10,000.
“Joe Carroll’s research on colorblindness represents a terrific example of cross disciplinary research,” says Donald T. Miller, associate professor of Optometry at Indiana University. “The project highlights the significant resolution advantage of adaptive optics technology and demonstrates the enormous potential this technology has for addressing unanswered clinical and scientific questions about human vision.”
“This research is really an indicator of how powerful adaptive optics can be,” says Carroll. “With it, we’ll be able to understand how our vision works in far more detail, and help to quickly diagnose and treat disease more effectively.”