A layer of "dark cells" that keeps light-sensing cells in our eyes healthy has been photographed in a living retina for the first time.
The ability to see this nearly invisible layer could help doctors identify the onset of many eye diseases long before any symptoms surface.
"Our goal is to figure out why macular degeneration, one of the most prevalent eye diseases, actually happens," said David Williams, optics professor at the University of Rochester.
"Macular degeneration affects one in 10 people over the age of 65, and as the average age of the US population continues to increase, it is only going to get more and more common," said Williams.
"We know these dark retinal cells are compromised by macular degeneration, and now that we can image them in the living eye, we might be able to detect the disease at a much earlier stage," he added.
In 1997, Williams' team was the first to image individual photoreceptor cells in the living eye, using a technique called adaptive optics, which was borrowed from astronomers trying to get clearer images of stars.
To image the dark cells behind the photoreceptors, however, Williams employed adaptive optics with a new method to make the dark cells glow brightly enough to be detected.
The cells, called retinal pigment epithelial, or RPE cells, are nearly black, and form a layer that recharges the photoreceptor cells of the eye after they are exposed to light, Williams explains.
The photoreceptors contain molecules called photopigments. When light strikes these molecules, they absorb the light and change shape, sending a signal to the brain indicating they 've "seen" light.
Besides, RPE layer keeps the photoreceptors healthy by collecting and storing toxic waste products that are produced during the process of regenerating the photopigment, said a Rochester release.
The findings were published in Thursday's issue of Investigative Ophthalmology and Visual Science.