The brain can learn to see in later life even if it has been deprived of visual input early on, work suggests.
Some blindness is reversible
One woman, who had her vision restored at the age of 12 by a cataract operation, performed almost normally on vision tests at the age of 32.
US experts say their studies show the brain is malleable in older children - which was doubted previously - and that the risks of surgery can be worth it.
And they have launched an initiative to treat blind children living in India.
About 450,000 children in India are blind, and many of those cases are preventable.
Most of the affected children live in remote areas where eye care is not available, and have conditions that could easily be treated, such as cataracts, vitamin A deficiency or conjunctivitis.
The Massachusetts Institute of Technology team hope to reach more of these children through Project Prakash.
Lead researcher Pawan Sinha explained that as a result of their work already, eye doctors were more willing to treat older patients, which they previously thought would be hopeless.
"Before our collaboration with them, they would be very reluctant to treat children older than five or six years of age, but now they are much more willing to identify older children and treat them."
He explained that his initial interest had been sparked by the case of the 32-year-old woman they studied, who they called SRD.
Before her surgery, SRD could distinguish between light and dark, but could not make out form or pattern.
Twenty years after the operation, which she had when she was 12, SRD's vision was as good as anyone with normal eyesight.
Surgery restored SRD's sight
On tests, she had near normal abilities and was able to recognise objects and faces, judge depth order and match 2D and 3D shapes, Psychological Science journal reports.
Things she did struggle with was visualising objects with her eyes closed and judging people's gaze when based on the direction of people's heads rather than where their eyes were looking.
Studies in animals have suggested a "critical period" for learning how to see. Kittens, for example, have very limited recovery of vision after being reared for the first few months in complete darkness.
But Mr Sinha's work suggests this is not the case in humans. They plan more work to track the precise order and mechanism of visual skill development in children who have their sight restored.
Tragically, SRD recently died in a road accident. The researchers are contributing funds to help her 9-year-old daughter, who is now living by herself in a hostel for the blind.
Sonal Rughani, an RNIB spokesperson, said: "Whilst these findings are fascinating, this single case study raises questions about the accepted ideas about the development of visual function.
"In each case where delayed visual development causes visual loss, the patient's ophthalmologist can best advise on the course of action as each case of visual impairment is complex."