A partial restoration of sight is possible also in individuals blind from birth, thanks to the most recent advances in research. However, a group of researchers of the Mind/Brain Center of the University of Trento and of the University of Montréal in Canada, discovered that the functional reorganization of the brain happens also in individuals who, for a long period, experienced a long sense deprivation which could impede a complete sight restoration.
“We were lucky enough to study the rare case of a patient, visually impaired since birth, whose sight was rapidly restored during her adult life, following keratoprothesis implant surgery, i.e. the replacement of the cornea with an artificial cornea, and specifically a Keratoprothesis Boston, in the right eye”, Giulia Dormal of the University of Montreal explained, being the coordinator of the study. “On the one side our results show that the visual cortex maintains a certain degree of plasticity - i.e. the capacity of the brain to tune its activity according to the experience - also in individuals visually impaired since birth. On the other side we discovered that, even months after the surgery, the visual cortex does not restore its complete normal functioning”. The visual cortex is the part of the occipital lobe responsible for the processing of the electric inputs coming from the eye.
In blind individuals the occipital cortex responds also to stimuli coming from other sense organs, such as hearing and touching, thus partially compensating the loss of sight. “The brain tuning is fundamental. However it challenges the sight restoration of individuals who undergo a transplantation, because the cortex - after its reorganization - may not be able to process visual inputs any longer”, Giulia Dormal explained.
To better understand the importance of this phenomenon researchers examined the 50-year-old Canadian female patient through a set of behavioural and neurophysiological tests. They monitored, before and after the surgery, the changes of the sight and the brain anatomy, as a response to visual and sound stimuli. Therefore the team of researchers used the functional MRI to record the brain activations of the patient during the performance of specific visual and hearing tasks and then compared them with the activations of individuals with normal sight and individuals blind since birth, while performing the same tasks.
“Before the surgery the patient presented a structural and functional reorganization of the occipital areas typical of individuals with a long sense deprivation. Therefore we proved the possibility of a partial recovery of the previous functions, after the sight restoration in adult age”, Olivier Collignon - neuroscientist at CIMEC - MIND/BRAIN CENTRE and coordinator of the research - explained. “Considering the significant recent advances in the technological solutions which allow for the sight restoration, these results play a significant role in the clinical implications to foresee the possible results of transplantations in patients to be operated”.
The study suggests that the eye surgery may achieve good results, also in adults severely visually impaired since childhood. However, it is important to warn that “The observed restoration in the visual cortex, in terms of minor response to sound stimuli and the gradual increase of response to visual stimuli and the density of the brain, is not complete. Indeed seven months after the surgery, some areas continue to respond weakly to sound stimuli, despite the simultaneous response to visual inputs”. This overlap may be the reason why some features of sight, in spite of the gradual improvements, still remain below standard even seven months after the transplantation”.
The clinical implications are twofold: “The results of our research pave the way for the systematic clinical use of the pre-surgery MRI as a prognosis tool regarding the efficacy of the transplantation. Further, they open up ways for specific rehabilitation programmes after sight-restoration surgery”, according to Collignon.
The research “Tracking the evolution of cross modal plasticity and visual functions before and after sight-restoration” by Giulia Dormal, Olivier Collignon et. al. was published in the Journal of Neurophysiology on 17 December 2014.
The study was financed by the Canada Research Chair Program, Canadian Institutes of Health Research, Saint-Justine Foundation, the European Research Council (the starting grant MADVIS coordinated by professor Olivier Collignon), Veronneau Troutman Foundation, Fonds de recherche en ophtalmologie de l’Université de Montréal, PAI/UIAP grant PAI/33 and the Belgian National Fund for Scientific Research.