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How does the brain adapt to the restoration of eyesight?

Vision

With all the scientific research that have taken place in the field of vision and eyesight, it has become possible for eyesight's to be restored even in people who have been blind for their life. But, in a recent study, the scientists at the University of Montreal and the University of Trento discovered that the visual restoration may never be 100%. This is because a rewiring of the senses that occurs in the brains of the long-term blind may never be complete.

Giulia Dormal who led the study, said that they had the opportunity to study a very rare case of a woman who had very low vision since birth. Her vision was suddenly restored in adulthood when she underwent an implantation of a Boston Keratoprosthesis in her right eye. It is known that the visual cortex maintains a certain degree of plasticity which means that it is flexible and has the capacity to change as there is a change in a function or experience like the restoration of vision in an adult person who had with low vision since early life. The visual cortex is the part of the brain that processes information from our eyes. However, after several months of the surgery, it is also discovered that the visual cortex is not functioning to its 100% potential.

Some very interesting observations have been made in cases of untreatable blindness. The occipital cortex – the part of the brain normally devoted to vision, becomes responsive to sound and touch in order to make up for the loss of vision. Some reorganization and rewiring of the brain occurs for this to happen. So, when such people undergo eye surgery to recover vision, the reorganized occipital cortex faces another challenge and it may not be able to restore itself to process vision anymore after having spent years in the dark.

To find out how much of a problem it can be, the researchers worked with the patient, a 50 year old Quebec woman. They conducted several behavioral and neurophysiological measurements prior to and after surgery to track changes in her sight and brain anatomy, and in the way her brain responded to sights and sounds. He was made to undergo MRIs and various visual and auditory tasks. Her scans were then compared with scans of people with normal eyesight and people with untreatable blindness who had performed the same tasks.

Oliver Collignon, Superviser of the research said that they could show that there was some structural and functional reorganization in the occipital regions in this patient before surgery because of the longstanding visual impairment. Some of these reorganizations can be partially reversed by visual restoration in adulthood. Since, there has been important advances in visual restoration techniques, such findings are crucial for blind individuals who are candidate to such interventions.

The study concluded that eye surgery in individuals who have had a life time of profound blindness can have a positive result. However, an important factor to take into consideration is that the decrease in auditory-driven responses and the increase in both visually-driven responses and grey matter density with time are not total.

Dormal said that auditory-driven responses were still evidenced in certain regions of the visual cortex even 7 months after surgery, and these responses overlapped with some visually-driven responses. That could be the reason why even after showing some improvement, some aspects of vision remained below normal range even after 7 months of surgery.

These findings open the door to the use of functional magnetic resonance imaging before surgery as a prognostic tool for visual outcome. It can also help in the development of adapted rehabilitation programs following visual restoration.

References

http://medicalxpress.com/news/2015-01-brain-eyesight.html

http://www.sciencedaily.com/releases/2015/01/150119082752.htm