Blind fish show eyes can grow back

July 28, 2000
Web posted at: 1:34 PM EDT (1734 GMT)

WASHINGTON (Reuters) -- Researchers said on Thursday they had caused eyes to grow in fish that have been blind for aeons -- simply by inserting a lens from sighted fish.

They said the lens seemed to send out signals that instructed the eyes in the blind cavefish to grow -- a finding that sheds light on how eyes evolve and develop.

A fish known as Astyanax mexicanus lives deep inside caves off the coast of Mexico where there is no light. Millions of years ago it had eyes but soon after it starts growing in the egg, the eyes start to degenerate and the fish are born blind.

Fish of the same species that live on the surface, where there is light, grow eyes and see normally.

"Our system deals with fish of the exact same species, but their living space and behaviour greatly differ," Yoshiyuki Yamamoto of the University of Maryland said in a statement.

He and biology professor William Jeffery did tests to see what it would take to get the eyes back in the cave fish.

They implanted a lens from the eye of a surface-dwelling fish into a cave-fish cousin and then watched to see what would happen.

Within eight days, an eye started developing from underneath a flap of skin, they reported in the journal Science.

After two months the cave fish had grown a large eye with a distinct pupil, cornea and iris, they said. The retina of the eye had photoreceptor cells known as rods.

Yamamoto said he was not sure what the lens did to stimulate development of the eye. "Maybe some growth factor but we are not sure what kind of growth factor," he said in a telephone interview.

He said the lenses of eyes were known to secrete a variety of growth factors, which are compounds that, as the name implies, stimulate cell growth and development.

"This offers clues about what sort of molecules are involved in eye growth of any vertebrate and it shows the growth of an eye is controlled in a large part by the lens," Jeffery said in a statement.

He said the finding might one day be useful to doctors.

"Though we are not working with human patients, these findings could someday prove useful to our colleagues in clinical practice," Jeffery said.

"Eye surgeons continue to make advances in the field of blindness research, including exciting new processes such as cornea transplantation," he added.

"Our group hopes to contribute fundamental insights into the genetic factors involved in eye development and growth."

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