A research team led by University of Maryland has found a new hope for treating "lazy eye" and other serious visual problems that are usually permanent unless they are corrected in early childhood.
Amblyopia afflicts about three percent of the population, and is a widespread cause of vision loss in children.
It occurs when both eyes are structurally normal, but mismatched - either misaligned, or differently focused, or unequally receptive to visual stimuli because of an obstruction such as a cataract in one eye.
During the so-called "critical period" when a young child's brain is adapting very quickly to new experiences, the brain builds a powerful neural network connecting the stronger eye to the visual cortex.
But the weaker eye gets less stimulation and develops fewer synapses, or points of connection between neurons.
Over time the brain learns to ignore the weaker eye.
Mild forms of amblyopia such as "lazy eye" result in problems with depth perception. In the most severe form, deprivation amblyopia, a cataract blocks light and starves the eye of visual experiences, significantly altering synaptic development and seriously impairing vision.
Because brain plasticity declines rapidly with age, early diagnosis and treatment of amblyopia is vital, neuroscientist Elizabeth M. Quinlan, an associate professor of biology at UMD, said.
If the underlying cause of amblyopia is resolved early enough, the child's vision can recover to normal levels.
But if the treatment comes after the end of the critical period and the loss of synaptic plasticity, the brain cannot relearn to see with the weaker eye.
"If a child is born with a cataract and it is not removed very early in life, very little can be done to improve vision," Quinlan said.
"The severe amblyopia that results is the most difficult to treat. For that reason, science has the most to gain by a better understanding of the underlying mechanisms," she said.
Quinlan, who specializes in studying how communication through the brain's circuits changes over the course of a lifetime, wanted to find out what process controls the timing of the critical period of synaptic plasticity.
If researchers could find the neurological on-off switch for the critical period, she reasoned, clinicians could use the information to successfully treat older children and adults.
The study is published in the peer-reviewed journal Neuron.