April 30, 2007 — Amblyopia, or “lazy eye,” may be reversible in adults, according to preliminary tests done on rats.

The experiments were done in Italy by Alessandro Sale, PhD, and colleagues. Sale works in Pisa, Italy, at the Scuola Normale Superiore.

In amblyopia, one eye is stronger than another. If detected at an early age, it can be corrected. But amblyopia recovery has proven to be harder in adults.

Sale’s team studied 69 adult rats with amblyopia. The researchers sewed the eyelid on the rats’ stronger eye shut, forcing the rats to use their weaker, “lazy” eye.

The researchers split the rats into two groups. In one group, the rats lived in pairs in standard cages. The other group of rats lived in what the researchers call an “enriched environment.”

In the enriched environment, groups of at least six rats shared big cages that had several food sources, a running wheel, and toys, tunnels, stairs, and shelters that were frequently changed.

Rats in the enriched environment “spend many hours per day exploring the environment,” Sale tells WebMD via email.

The rats in the enriched environment reversed their amblyopia. The effects lasted at least two weeks after the rats were removed from the enriched environment, the study shows.

The rats’ brains apparently changed to adapt to the constantly changing enriched environment. Those brain changes may have overridden amblyopia, the researchers suggest.

But Sale says it is “absolutely necessary” to note that the effects “may not apply in the same measure to other species with much higher visual acuities,” including humans.

“Possible applications in humans need further research and suitable caution, although they are more likely than those of other studies using pharmacological treatment,” Sale says.

The study appears in the advance online edition of Nature Neuroscience.