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If a congenital blind person gets eye sight (either hypothetically, or in the near future due to advancements in technology), will their brain be able to handle that information, or will it become overloaded?

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Short answer
Congenitally blind people can regain visual function at a later age. However, the longer they were blind for, the lesser their visual function will be and the longer it takes for them to rehabilitate. Immediately after receiving first eye sight, the visual experience of congenitally blind people is not comparable to that of normally sighted people. They may need months of rehabilitation training to make sense of their newly acquired sight, especially when they were blind for many years.

Background
There are various treatments for blindness to date. Since you mention technology in the question, visual prosthetics come to mind. Visual prosthetics already exist, and there are at the time of this writing two retinal implant systems commercially available; the Argus II and the alpha-IMS (Stronks et al., 2014). Retinal implants are used to provide a crude form of vision to those with severe retinal degenerations, such as end-stage retinitis pigmentosa. However, visual prosthesis technology is still in its infancy and at the time of this writing, only people that lost their vision later in life are implanted. So there is as yet no data available on your question whether congenitally blinded people can benefit from it.

However, from a related technology, cochlear prostheses, we know that the earlier a congenitally deaf person is implanted, the better the result is. Early-implanted folks can learn to understand speech, and develop speech relatively normally. Nowadays infants as young as 3 months receive cochlear implants. Early implantation is critical, because the brain is plastic. When the auditory cortex is not used due to sensory deprivation, it will quickly be taken over by other cortical areas. Once this cortical recruitment progresses for too long, a person can never gain functional hearing at the level reached by early-implanted people (Teoh et al., 2012).

Very likely the same holds for visual prosthetics. A congenitally blind person should be implanted as soon as possible after birth. This, because it is known that cross-modal plasticity results in the visual cortex being recruited for tactile and auditory processing. As with the auditory system, once this restructuring progresses long enough, my educated guess is that a person will never be able to develop functional vision comparable to an early implanted subject. And this is the reason why at present, only the acquired blind receive retinal implants.

For example, a case report of a subject who was blind for over 50 years regained his eye sight after corneal surgery. Although the subject did develop visual function after the surgery, visual performance remained greatly compromised. This was particularly evident when the tasks targeted finer levels of perceptual processing Siki et al., 2013).

Important clues are being obtained in the "Project Prakash", an ambitious project to provide opthalmological support to the people in poor, rural parts of India. Routine cataract surgeries have been performed in people with cataracts, including in people with congenitally present cataracts, where the lenses in the eyes were opaque from birth. Older kids, like teenagers, that were blind from birth typically show non-functional vision after the bandages are removed after surgery. It is thought that these first moments for the newly sighted are blurry, incoherent, and saturated by brightness, akin to swirls of colors that do not make sense as shapes or faces or any kind of object. However, after months of rehabilitation, they do develop functional vision. The lower-level markers of visual function never reach normal values. Specifically, they continue to suffer from poor visual acuity - the gold standard to assess visual function. Nonetheless, some higher-order aspects of vision do seem to be improving. Within a week to a few months after surgery, the children can match felt objects to their visual counterparts (source: The New Yorker, August 28, 2014).

References
- Siki et al., Iperception (2013); 4(8): 498–507.
- Stronks et al., Expert Rev Med Devices (2014); 11(1):23-30
- Teoh et al., Laryngoscope (2004); 114(9): 1536–40

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