NEW IMPLANT RESTORES BALANCE IN PATIENTS WITH SEVERE INNER EAR DISORDER
Learning from hearing aids
Problems with the inner ear and vestibular system can substantially affect patients’ quality of life. The most extreme variant is bilateral vestibular hypofunction, which can affect gait and balance. Patients are more likely to experience falls, have visual blurring and chronic “dizziness”, even when sitting or lying down. About 120,000 adults in Europe, and 3 million worldwide, are estimated to have bilateral vestibular dysfunction.1 There is no current treatment for the disorder, other than patients learning compensatory strategies.2 But researchers from Switzerland and the Netherlands have developed a vestibular implant, which delivers electrical currents directly to the vestibular nerve itself, to artificially restore lost vestibular function.
“Our group has been working in this field since 2007. The idea came from the clinical accomplishments of cochlea implants, the most successful nueroprosthesis to date”, said Dr Angelica Perez Fornos (Division of Otorhinolaryngology Head and Neck Surgery, Geneva University Hospitals and University of Geneva). “Our team, a pioneer in the development of cochlear implants, is trying to build on this experience to design a vestibular implant.”
Currently there are no vestibular plants commercially available. But a few research groups are working on variants of an implant. The device under development by Dr Fornos and her group comprises a cochlear implant as well as a vestibular implant, that aims to work as an “artificial inner ear”. The vestibular system works by sensing motion with the semicircular canals; three tiny, fluid-filled tubes located in the innermost part of the ear. When your head turns, the liquid inside the semicircular canals moves in turn and moves tiny hairs inside the canals, and this provides feedback on balance. The group tried to recreate this function in the inner ear.
The group tested their device on 13 patients to see if the implant could activate the vestibulo-colic pathway and vestibule-colic reflex. A gyroscope motion sensor (that senses orientation) was fixed on patients’ heads, and this imitated sensing motion like the vestibular system. This motion information was fed to a dedicated processor that communicates with the implanted device transcutaneously. The implant simulator then delivers an “artificial” motion signal directly to the ampullary branches of the vestibular nerve via implanted electrodes. Patients were asked to do various tasks with the motion sensor on, such as taking a few steps with their eyes closed. And the results confirmed that the device was able to successfully restore the vestibule-colic reflex and generate controlled postural responses in patients. The team were also able to activate the vestibulo-ocular reflex, and improve visual ability in patients with symptoms of oscillopsia, which is visual blurring that occurs during head movements, a symptom that can affect almost 70% of patients with bilateral vestibular dysfunction.
THE DEVICE WAS ABLE TO SUCCESSFULLY RESTORE THE VESTIBULE-COLIC REFLEX AND GENERATE CONTROLLED POSTURAL RESPONSES IN PATIENTS.
Bilateral vestibular hypofunction affects patients’ quality of life in many ways, including reduced physical activity which can lead to social isolation. The research group hopes that their technology will one day make a big difference to patients’ lives. In addition to balance, vision and hearing, functional vestibular deficits can impact patients in psychiatric and cognitive difficulties ranging from agoraphobia, depression, anxiety, memory shortfalls and difficulties in multitasking, explained Dr Fornos.
Since the vestibular implant project was born in Geneva in 2007, the group has expanded as researchers from the University of Maastricht, the Netherlands joined the team. “Since then we have established a very close and fruitful collaboration,” said Fornos, “Our project would not be successful without our multidisciplinary team of scientists, engineers, ENT doctors who specialise in vestibular science and inner ear surgery, biologist and physicists.”
"Understanding the misunderstood”
The field’s main barrier is poor understanding of vestibular deficit. The exact causes of the condition are still not known, the function of the vestibular system is still not clearly understood and is difficult to measure, explained Dr Fornos. Initially Dr Fornos worked with retinal implants and moved onto cochlear and vestibular implants. “I think what brought me into this field was hoping to ‘understand the misunderstood’. Knowledge of the fundamental aspects of vestibular function has been extremely difficult until now. A vestibular implant offers an unprecedented opportunity to, on one hand help a population of patients in need, and on the other hand move a field forward.”
The team’s next steps are to carefully investigate how and to what extent each of the vestibular pathways can be selectively activated and how each evoked vestibular response contributes to the restoration of everyday activities.3 It is hoped that this further research will optimise processing and stimulation strategies to improve rehabilitation in patients but also to improve understanding of the vestibular system and its pathways.
Kingma H, Felipe L, Marie-Cecile G, et al. Vibrotactile feedback improvesbalance and mobility in patients with severe bilateral vestibular loss. J Neurol 2019; 266: 19-26.
Veda, Life Rebalanced: Bilateral Vestibular Hyopfunction.
https://vestibular.org/BVH#:~:targetText=Bilateral%20Vestibular%20Hypofunction,see%20clearly%20during%20head%20movements. Accessed November, 2019.
Perez Fornos A, van de Berg R, Armand S, et al. Cervical myogenic potentials and controlled postural responses elicited by a prototype vestibular implant. J Neurol 2019; 266: S33-S41.