Bad eyesight runs in my family. Nearly all of us have glasses and struggle with some type of vision loss. One of my cousins has had glasses since first grade and her eyesight has deteriorated to the point where she is legally blind and probably shouldn’t drive at night, no matter how much she protests otherwise.

Though it hasn’t presented in my family, a typical eye disorder for children is called amblyopia and it’s when the brain ignores one eye in favor of the other. This disorder is generally caused a lazy eye to develop, or amblyopia can also develop when one eye has cataracts and the other doesn’t. The main treatment for amblyopia is to patch the stronger eye, but that only works for children under the age of seven. After seven, ocular dominance and plasticity is established and is hard to correct. 

Recently, researchers found a brain circuit that may help fix amblyopia even after the age of seven years old. To understand how this work, we need to first understand why amblyopia typically remains untreatable in teenagers and adults.

As the eyes develop they try to connect to the binocular zone, or the area that takes in what the eyes see. If one eye is weakened, the other will most likely become the dominate eye and restrict the other eye from making a secure connection. When the connection has been made by an eye, the process is called ocular dominance, and this is an example of the brain’s ability to adapt based ones experience, which is called plasticity.

These connections must be made in a critical time period, which ends around the age of seven. After this point, it’s hard to make the eyes form different connections. The idea behind the new study is to delay plasticity because this is what makes the connections hard to change. Once the brain has settled on a routine, it doesn’t like to change its mind. However, plasticity can only happen when the firing rate of the brain cells are above a certain threshold, so the idea is to keep the eyes below the threshold for a certain amount of time so that the connections to the binocular zone can be remodeled.

Researchers found a potential method of remodeling the connections in a brain circuit that normally inhibits the firing rate of cells. When the dominate eye is patched for a period of 24 hours, the threshold predictably drops, but then rises to normal levels in both eyes when the patch is removed because the circuit that usually inhibits this temporarily weakens. By manipulating this circuit, doctors may be able to fix amblyopia in teenagers and adults by basically rebooting ocular dominance and delaying plasticity.

Source: NIH/National Eye Institute (2013, August 25). Researchers find essential brain circuit in visual development. ScienceDaily.

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