Fibre optic hearing aids demonstrated

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Researchers in Austria have tested a pair of implantable hearing aids based on fibre optic technology. The devices, which detect the tiniest ossicle movements and stimulate the acoustic nerves, could overcome limitations of existing implantable hearing aids. 

Published on 30 April in Biosensors and Bioelectronics, the tests produced important findings on future use of the technology on humans. The research was carried out by a joint Austrian-Serbian team, which included the Karl Landsteiner University of Health Sciences. 

Implantable hearing devices are beneficial because they do not have to be worn on the outside of the ear, which can be uncomfortable and cause the patient other problems. However, the microphones, which receive sounds and transform them into impulses for the acoustic nerves, have limited performance over time.

'Even state-of-the-art hearing aids often require parts outside the ear. This has many disadvantages for people who wear hearing aids: they can be stigmatised if the device is visible, parts of the ear often become inflamed and the wearer’s own voice can sound distorted. Fully implantable hearing aids can overcome these problems – but the technology still needs to be fine-tuned. And that’s what we are working on,' said Professor Georg Mathias Sprinzl, head of the Ear, Nose and Throat Department at St Pölten University Hospital. 

One advance could be the use of contact-free fibre-optic measuring technology that picks up vibrations in the ossicles - small bones within the middle ear, which transmit sounds from the air to the network of passages within the ear. This technology now tested the technology under realistic conditions, and could potentially allow the microphone to be positioned inside the ear.

The technology is based on low-coherence interferometry, a method which picks up superimposed sound waves. The team used this approach for the optical measurement of nanometre-sized ossicle vibrations. As Professor Sprinzl explained: 'The ability to pick up sound from the ossicles is a huge advantage because it fully preserves the natural amplification function of the outer ear and the eardrum. On the technological side, this also minimises signal distortion and feedback.'

With a view to deploying the system in the human ear, Professor Sprinzl and his colleagues needed to address a number of fundamental requirements. For example, they had to develop the operative procedure for the implantation, as well as the means of targeting the laser used for sensing. Sprinzl, who performs more than 1,000 implants of various types of hearing aid each year, noted: 'Obviously, we did not carry out this development work on people. Instead, we used artificial and animal models, which allowed us to optimise the quality of the ossicle vibration sensing system.'

The recently-published findings confirm the effectiveness of the technology and that, in principle, it could be used inside the ear for long periods. In these initial tests, the team found that the laser beam, which is critical for sensing vibrations, remained accurately aligned with the selected ossicle for five months. The team’s measurements also showed that the system can distinguish between the sounds to be transmitted and background noise, although more work will be required in this respect in future. Aspects such as system miniaturisation and electricity consumption will also be addressed by the team, which comprises Acmit GmbH, the Medical University of Vienna, the University of Belgrade, KL Krems and ENT specialists.

The project team includes surgeons working alongside engineers and software developers. KL Krems’ participation in this cutting-edge innovation project, which is supported by NÖ Forschungs- und Bildungsges.m.b.H., the Lower Austrian research and education agency, once again underlines the university’s focus on niches in bridge disciplines related to health policy.