A study in mice reveals an elegant circuit within the developing visual system that helps dictate how the eyes connect to the brain. The research, funded by the National Institutes of Health, has implications for treating amblyopia (also known as “lazy eye”), a vision disorder that occurs when the brain ignores one eye in favor of the other. Amblyopia is the most common cause of visual impairment in childhood, and can occur whenever there is a misalignment between what the two eyes see—for example, if one eye is clouded by a cataract or if the eyes are positioned at different angles. The brain at first has a slight preference for the more functional eye, and over time—as that eye continues to send the brain useful information—the brain's preference for that eye gets stronger at the expense of the other eye. Patching the strong eye can help correct amblyopia. But if the condition isn't caught and corrected during childhood, visual impairment in the weaker eye is likely to persist into adulthood. "Our study identifies a mechanism for visual development in the young brain and shows that it's possible to turn on the same mechanism in the adult brain, thus offering hope for treating older children and adults with amblyopia," said Joshua Trachtenberg, Ph.D., an associate professor of neurobiology at the David Geffen School of Medicine, University of California, Los Angeles (UCLA). The study was published online on August 25, 2013 in Nature. Within the brain, cells in a limited region called the binocular zone can receive input from both eyes. During brain development, the eyes compete to connect within this zone, and sometimes one eye prevails—a process known as ocular dominance. Ocular dominance is a normal process and is an example of the brain's ability to adapt based on experience—called plasticity. But it can also set the stage for amblyopia.
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