Researchers have stopped vision decline in dogs with an inherited disease that causes blindness.

The gene therapy technique they used may someday stop vision loss in humans.

Retinitis pigmentosa (RP) is an eye disease that causes the light-sensitive cells in the retina - the rods and cones - to die.

The loss of eyesight normally happens slowly, over years or decades.

RP is caused by a genetic mutation, so scientists at the University of Pennsylvania's Scheie Eye Institute and veterinary school teamed up to see if injecting a normal version of the mutant gene into dogs with the disease would stop the die-off of those light-sensitive cells.

"What we were able to show is that we can stop the degeneration, we can stop the cell death of both the rods and the cones," says University of Pennsylvania veterinary ophthalmologist William Beltran, the study's lead author. "What the gene therapy approach is doing is, in fact, rescuing those cells that are diseased but have not died yet."

Canine RP is like the human variety, which makes dogs a good model for studying the disease and possible treatments.

Beltran says the gene therapy appears to be safe and effective in stopping the progression of the disease, but he cautions that it can't do much to reverse vision loss. It can't restore the light-sensitive cells that have died, and it can't grow new ones.

Beltran says tests in humans are still an estimated four-to-five years off. He wants to do more animal testing to see, for example, if the gene therapy has a long-lasting effect.  

"And the reason for doing so is that the likelihood is when we get to treat patients, we will be treating individuals that are at a rather later stage of degeneration."