A team of international researchers, including from the Indian Institute of Technology (IIT) Delhi, has found evidence of brain structures that underlie sight recovery in people born blind, and may help treat the condition.

The team included 23 congenitally blind patients (aged 7-17 years) from Uttar Pradesh with dense bilateral cataracts, who received cataract surgery at different stages of adolescence.

The findings, published in the journal The Proceedings of the National Academy of Sciences (PNAS), showed that improvements in visual functions are linked to changes in white matter pathways, which connect neurons in different brain regions.

The team studied many pathways, but only those involved in high-order visual functions, such as face recognition, were directly linked to the visual improvement.

Moreover, researchers saw that the patient's amount of change in late visual pathways, specifically the posterior callosum forceps, predicted the amount of behavioural improvement. This is a new result that identifies the location of brain changes responsible for behavioural improvement.

They also confirmed that cataract surgery has a greater impact on visual function and brain plasticity if received at younger age, but recovery is still possible even if the eye surgery is received later in adolescence.

The results suggest that sufficient plasticity remains in adolescence beyond the critical period for visual development, allowing patients to partially overcome abnormal visual development and help localise the sites of neural change underlying recovery in blind teenagers.

There is therefore a window of time wider than previously thought, during which sight-recovery surgeries can be useful to improve visual perception by altering structural brain plasticity.

"There is a general notion known as 'critical period for sensory development' that kids who are born visually impaired (due to cataract) and continue in that same condition for a few months or years, can't get back their visual function later part of life, even if they get back their sight by miracle. But this appears not to be true in many cases," said Prof. Tapan K. Gandhi, Professor of AI, Department of Electrical Engineering at IIT Delhi.

"Current medical facilities can treat defects in lenses and corneas, and the brain can then begin to learn about the visual world," he said.

The research sheds light on the definition of the sites of neural change related to sight-recovery, which can guide the development of treatments that attempt to induce neural plasticity through behavioural and surgical interventions.

"The new insights uncovered by our team challenge accepted limitations of sight-recovery surgeries, creating an opportunity for the expanded use of these surgeries that will make many more cases of blindness treatable, worldwide," said Bas Rokers, director at Neuroimaging Centre at New York University- Abu Dhabi.

"Our work also offers evidence to support the call for the scientific community to reassess the critical period for visual development in adolescents," he added.