Gingersnap, a 4-year-old Abyssinian, rolled lazily on the examining table while veterinary ophthalmologist Kristina Narfstrom rubbed the cat's cinnamon-colored head.
Then, using a special viewer, Narfstrom peered deep into Gingersnap's eyes to measure her losing battle with a disorder that is slowly killing her retinas, the thin film at the back of the eyeball that makes sight possible.
"By the time she's 5, she'll probably be blind," said Narfstrom, a professor at the University of Missouri.
Gingersnap's condition is similar to retinitis pigmentosa, an incurable genetic disease in humans that strikes one out of every 3,500 Americans and often causes blindness. Narfstrom, who discovered the feline version of the disease among Abyssinians in her native Sweden, is implanting special silicon chips in partially blind cats in a bid to help replace or possibly repair diseased retinas in humans.
Retinitis pigmentosa attacks the eye's photoreceptor cells, also called rods and cones, that register light and color.
The chips, which provide their own energy, have shown encouraging results in clinical human trials, in some cases improving sight in people with retinitis pigmentosa or at least slowing the disease's development. Narfstrom said chips have been implanted in 30 people.
Narfstrom's cats will help researchers fine-tune the chips' performance and train physicians on surgical techniques to implant the devices, because the structure of cat eyes is similar to that of humans.
The 2-millimeter-wide chips, developed by Optobionics Corp. of Naperville, Ill., are surgically implanted in the back of the eye. Each chip's surface is covered with 5,000 microphotodiodes that react to light, sending electric signals along the eye's optic nerve to the brain.
"We're placing it right where the photoreceptors are and if they're lacking, this is supposed to replace what they're doing," she said. "At this point, it's impulses of light they're seeing (as opposed to images), but the aim of the research is to get more information out of the chip."
Besides helping slow the advance of the disease, studies suggest that the electric currents generated by the chips may be regenerating damaged photoreceptors surrounding the implants.
Narfstrom said she should know in about two years whether the implants are actually encouraging retinal cells in her cats to grow.
The Optobionics chip is just one of many research paths now swarming with scientists looking for ways to protect and restore sight.
Besides genetic therapy, which is seen as a good tool to fight hereditary disorders, researchers are also looking to use stem cells to rebuild damaged retinal cells. Others are looking for substances that could trick healthy retinal cells surrounding the photoreceptors to take over for their diseased counterparts.
Then there are the many attempts, like Optobionics, to create artificial sight. Some efforts include miniature video cameras that pipe images straight to the brain, devices that send signals to a network of miniature electrodes attached to the retina or chips that eventually could graft themselves to retinal cells, creating a cyborg-like system for producing images.
A French company is conducting trials for an implant that would release proteins in the eyeball to offset the damage done to retinal cells, perhaps indefinitely.
Tim Schoen, director of research development for the Foundation Fighting Blindness, a Baltimore area group that funds researchers, said technology to provide prosthetic sight is especially encouraging.
"This offers great hope to individuals who have completely lost vision," said Schoen, whose group is not involved in the Optobionics chip. "We can treat these patients with gene therapy, but once the photoreceptors die, we have to replace them with stem cells or one of these artificial methods."
Machelle Pardue, a researcher at Emory University and the Veterans Administration Hospital in Atlanta, who is working with Narfstrom on the Optobionics chip, said she's glad she's not the only one doing such research.
"I think it's helpful because we all have slightly different ideas and expertise," Pardue said. "In some respect, we are competing to find a product that will work, but that's advantageous to the patients because it provides an incentive to move forward."