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January 21 2014
Patients blinded by cataracts from an early age can learn to see after corrective surgery, suggesting that the brain can rewire itself long after the ‘critical window’ for development.
The findings from a recent study by US researchers suggest that the area of the brain which processes visual information, the visual cortex, maintains a degree of plasticity beyond infancy, and may be able to adapt even after years without visual stimuli.
It has long been held that core brain processes are laid down early on in life during a critical window of development and are then set. However, the findings indicate that the visual cortex may retain a level of adaptability, called neuroplasticity, in which the brain is able to reorganise and strengthen or cut connections and pathways.
The study looked at children in India who had developed cataracts in both eyes before the age of one. The children then received corrective surgery at eight years old or later, meaning they were effectively blind for an extended period of time.
The group aimed to study how contrast sensitivity developed once cataracts were removed, an indicator of visual processing of the brain. After the surgery, 11 patients were monitored for six months and administered iPad-based tests to measure contrast sensitivity – a basic function of vision allowing a person to distinguish between spatial patterns and backgrounds.
After six months, five of the children (aged 11 to 15) showed a significant gain in visual function, and two had seen an improvement of 30 times their original assessment.
The results indicate that their brains were able to adapt to process the flood of new information from their functioning eyes. In some cases, the rate of development was faster than that of infants.
It was typically thought that older children who required corrective surgery to restore vision had missed the critical window of development in which the brain lays down the brain processes needed for sight. However, the team have showed that patients with early-onset prolonged blindness can develop contrast sensitivity outside of this critical window of neuroplasticity.
“The dogma in neuroscience is that any improvement should be minimal at this stage,” said Dr Amy Kalia
, study author and post-doctoral fellow at the Massachusetts Institute of Technology. “I think it really extends what we think of as the window of plasticity in the visual brain,” she added.
The team are currently collecting data from fMRI scans to image the activity of the brain in these regions after surgery.
Dr Luis Andres Lesmes, of Adaptive Sensory Technology, who designed the contrast sensitivity test, and co-author of the study, said: “The study speaks to how incredibly plastic the brain is and how resilient it is.”
“Even if the brain is blind to visual experience for more than a dozen years, there remains potential for substantial visual development.”
The researchers hope to help children who have gained vision after prolonged blindness. “Many of these children get lost in the education system,” said Dr Kalia. “They go to blind school, then once they regain vision, the system won’t allow them to join the education stream at that late age.”
Commenting on the findings to OT
, Dr Dolores Conroy, Director of research at Fight for Sight
, said: "This study challenges established views that there was a development window for vision which closes at around 6-7 years of age and gives new insights into brain plasticity.
“The implications of this are far reaching and may lead to new approaches not only for children with treatable sight loss in developing countries but also deafness.”
Clara Eaglen, eye health campaigns manager for RNIB
, added: “This study is interesting as it helps to increase our understanding of how vision develops.
“Clearly further research is needed, across larger groups of participants, but it will be interesting to see how it progresses.”
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