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HomeminewsVisual System Shows Plasticity

Visual System Shows Plasticity

Children blind at birth as a result of cataracts have regained sight and there vision has continued to improve following cataract surgery, even after extended periods of blindness, according to researchers from the Schepens Eye Research Institute/Massachusetts Eye and Ear, Harvard Medical School (HMS) and Massachusetts Institute of Technology (MIT).

The research, published in Proceedings of the National Academy of Sciences (PNAS) Early Edition challenges the theory that deprivation of vision during critical periods of childhood development results in irreversible vision loss.

The researchers studied a unique population of paediatric patients who were blind during these critical periods before removal of bilateral cataracts.

According to the published study, they found improvement after sight onset in contrast sensitivity tests using an iPad-based assessment function, which measure basic visual function and have well-understood neural underpinnings. Their results show the human visual system can retain plasticity beyond critical periods, even after early and extended blindness.

“Our research group has been studying the development of vision in children who were blind from birth because of congenital cataracts,” said Senior Author Peter J. Bex, Ph.D., Senior Scientist at the Schepens Eye Research Institute/Mass. Eye and Ear and Associate Professor, HMS Department of Ophthalmology. “We have been measuring if and how their vision develops after surgery in late childhood and adolescence to remove cataracts, which enables sight for the first time. Our results show remarkable plasticity and vision continues to improve in many children long after the surgery…

“We showed that some patients developed substantial vision after 15 years of blindness. This visual change could not be accounted for by simple optical factors, either.”

The ‘critical period’ or the ‘critical window’ is a traditional concept in the field of neuroscience that suggests there is ‘plasticity’ or potential for development early in life. As people age past seven or eight years there is less and less plasticity in the visual system.

Researchers believe this concept influenced practitioners’ approach to treating children with amblyopia – it was once believed that if you didn’t treat amblyopia before a child turned eight the opportunity to save sight would be lost. In many cases this justified the decision to do nothing once the child had reached adolescence. Insights into plasticity and the potential impact of brain or sensory training following surgery over the past decade have changed this thinking.

Research to Aid Rural India

The researchers hope their work will aid problems of treatable blindness in India by providing surgeries free of cost to children with cataracts who would in many cases be left untreated due to the financial burden placed on families. In the Western world, children born with cataracts are typically treated in their first year of life.