Researchers at Cornell University said findings they made by fitting chickens with the wrong prescription lenses may lead to new treatments of human vision problems.
When young chickens wear spectacles, their eyes adapt by either growing faster or slower to correct for fuzzy images produced by the wrong prescription lenses, the researchers said Thursday."These findings are the first direct demonstration of . . . controlling growth of the eye," Howard Howland, a professor of neurobiology and behavior at Cornell, said in a statement.
Howland said that if the same effect operates in humans, it would mean that placement of lenses on the eyes of young children could affect the growth of their eyes.
Lenses normally prescribed for farsighted people caused week-old chickens' vision to defocus until their eye growth slowed and the chickens could see again. Lenses normally prescribed for nearsighted people also blurred chickens' vision, but they compensated by increasing their eye growth and regaining perfect vision, the study showed.
The chicken eyeglass experiments, published this month in Vision Research, also suggest a biochemical basis for regulating vision, and may lead to new treatments to help young eyes compensate for vision defects, Howland said.
"It's always seemed sort of a miracle that young eyes can grow, increasing in size several times as they mature, and still keep an image focused on the retina with all the internal parts changing," Howland said.
"Perhaps it is not surprising that the eye is in some way recording its own length by looking at whether it has a focused image on the retina and modulating its growth accordingly," he said.
To conduct the experiment, researchers at Cornell fitted young chickens with mask-like devices that held the lenses just off the bird's eyes.
At first the chickens compensated for blurred vision by changing the curvature of their corneas, which humans are incapable of doing, but within days significant changes in the rate of eye growth were noted, Howland said.
The distance between the corneas and retinas of chickens with positive prescription lenses became proportionally less, when compared to other dimensions of the growing eye, and focused images returned to the retina.
Chickens with negative prescription lenses experienced accelerated growth of their eyes.