Montreal University. Canada: Recent scientific advances have meant that eyesight can be partially
restored to those who previously would have been blind for life.
However, scientists at the University of Montreal and the University of
Trento have discovered that the rewiring of the senses that occurs in
the brains of the long-term blind means that visual restoration may
never be complete.
“We had the opportunity to study the rare case of a
woman with very low vision since birth and whose vision was suddenly
restored in adulthood following the implantation of a Boston
Keratoprosthesis in her right eye,” explained Giulia Dormal, who led the
study. “On one hand, our findings reveal that the visual cortex
maintains a certain degree of plasticity – that is the capacity to
change as a function of experience – in an adult person with low vision
since early life. On the other, we discovered that several months after
the surgery, the visual cortex had not regained full normal
functioning.” The visual cortex is the part of the brain that processes
information from our eyes.
Scientists know that in cases of untreatable blindness, the occipital
cortex - that is the posterior part of the brain that is normally
devoted to vision - becomes responsive to sound and touch in order to
compensate for the loss of vision. “This important brain reorganization
represents a challenge for people encountering eye surgery to recover
vision, because the deprived and reorganized occipital cortex may not be
capable of seeing anymore after having spent years in the dark,” Dormal
said.
In order to ascertain how much of a challenge this may be, the
researchers worked with the patient, a 50 year old Quebec woman. They
conducted behavioral and neurophysiological measurements before and
after surgery to track changes in her sight and brain anatomy, and in
the way her brain responded to sights and sounds. This involved taking
MRI images as she completed various visual and auditory tasks and
comparing her scans with scans that had been taken from people with
normal eyesight and people with untreatable blindness who had performed
the same tasks. “We show that structural and functional reorganization
of occipital regions were present in this patient before surgery as a
result of longstanding visual impairment, and that some reorganizations
can be partially reversed by visual restoration in adulthood,” said
Oliver Collignon, who supervised the research. “Because of important
advances in visual restoration techniques, such findings have important
clinical implications for the predictive outcome of blind individuals
who are candidate to such interventions.”
The study suggests that eye surgery can lead to a positive outcome
even when performed in adulthood after a life-time of profound
blindness. There is however an important caveat. “The recovery observed
in the visual cortex, that is highlighted by a decrease in
auditory-driven responses and by an increase in both visually-driven
responses and grey matter density with time, is not total,” Dormal
explained. “Indeed, auditory-driven responses were still evidenced in
certain regions of the visual cortex even 7 months after surgery, and
these responses overlapped with visually-driven responses. This overlap
may be the reason some aspects of vision, despite having improved with
time, still remained below normal range 7 months after surgery.”
The clinical implications of the research are two-fold. “Our findings
open the door to the use of functional magnetic resonance imaging
before surgery as a prognostic tool for visual outcome and pave the way
for the development of adapted rehabilitation programs following visual
restoration,” Collignon said.
About this study:
Giulia Dormal, Olivier Collignon and their colleagues published
“Tracking the evolution of crossmodal plasticity and visual functions
before and after sight-restoration” in the Journal of Neurophysiology on
December 17, 2014. The research received funding from the Canada
Research Chair Program, the Canadian Institutes of Health Research, the
Saint-Justine Foundation, the European Research Council (starting grant
MADVIS, ERC-StG 337573, the Veronneau Troutman Foundation, the Fonds de
recherche en ophtalmologie de l'Université de Montréal, PAI/UIAP grant
PAI/33, and the Belgian National Fund for Scientific Research. The
University of Montreal is officially known as Université de Montréal.