Vision was restored in amblyopic adult mice when exposed to visual stimuli while running. Amblyopia is a condition in which the brain does not develop properly to process visual information due to lack of visual experience when young. During early brain development visual experience is necessary otherwise amblyopia will result. When humans have amblyopia, glasses cannot correct vision to normal because the brain has learned to “turn off” visual processing.
The study was carried out at the Center for Integrative Neuroscience at the University of California in San Francisco. The lead author was Michael Stryker, who has worked on the problem of amblyopia for many years.
In the newly reported study, newborn mice were made to be amblyopic by having their eyelids sutured shut by the researchers. With the eyelids shut, the brain could not receive any visual stimulation. After the mice became adults, they were amblyopic and had a level of blindness. Usually, once the brain has reached a level of development that is considered to be adult, vision cannot be restored. This is the case for humans as well as animals.
In humans, one of the common causes of amblyopia is “lazy eye.” With lazy eye, one eye is misaligned from the other due to a difference in the lengths of the muscles that pull the eye left and right. If someone has lazy eye, their two eyes do not focus together and the brain receives a very different picture from each eye. Then the brain shuts down the information from one eye (the “bad” eye) and only works with the information from the other eye (the “good” eye). Amblyopia results from the bad eye being shut down. It has been commonly held that correction of amblyopia in humans must occur before age 8 years old, which is when it is thought that the brain reaches a critical stage of adulthood.
Correction of amblyopia in humans includes surgery to adjust the eye muscles so that the two eyes are aligned correctly or eye patching. Eye patching to correct amblyopia involves wearing an eye patch over one eye for a certain period of time and then switching the eye patch to the other eye for a while so that the brain receives information from each eye for a while equivalently.
Other causes of amblyopia besides lazy eye are congenital cataract or a droopy eyelid. When these situations occur, the process for preventing or treating amblyopia are similar to eye patching in that visual stimuli must be allowed to reach the brain. In the case of congenital cataract, the cataract in the cornea needs to be removed and a droopy eyelid would need to be surgically corrected to allow proper visual stimulation.
What is new and of particular interest in the recently published study by Stryker is that they were able to restore vision in adult mice that were amblyopic, and they used a simple method of letting them run to experience flowing visual stimulation. Visual stimulation alone and running without visual stimulation did not restore visual function. What was important was the combination of streaming visual stimulation while running. Showing that vision could be restored in amblyopic adult mice with visual exposure while running may offer new and exciting treatment suggestions for humans with amblyopia.
By Margaret Lutze