Vestibular implants in bilateral vestibular failure: current evidence and future directions

Bilateral vestibular failure (BVF) results from dysfunction of both vestibular apparatuses, leading to impaired gaze stabilisation, postural instability and oscillopsia; symptoms that significantly reduce functional independence and quality of life.¹ Patients frequently report difficulty walking in low-light environments, reading while in motion and maintaining balance during daily activities, often resulting in falls and notable psychosocial impact.² Given renewed international interest in vestibular neuroprostheses, a critical appraisal of current evidence is timely.^3–5

BVF has been estimated to affect approximately 28 per 100,000 individuals.¹ In a population of 5 million, such as New Zealand, this equates to over 1,400 patients, a figure likely to increase with population ageing. Thus, although often described as rare, BVF represents a clinically meaningful and growing source of disability. 

Current management focusses on vestibular rehabilitation, which promotes central compensation through reliance on visual and proprioceptive cues, and symptomatic strategies. While some patients derive benefit, rehabilitation is an inherently compensatory approach that does not restore vestibular sensory input, particularly in cases of complete bilateral loss.⁶

Vestibular implants are microelectronic devices designed to stimulate vestibular nerve afferents to restore vestibular function, drawing conceptually on the experience of cochlear implantation.⁷ Over the past two decades, preclinical and early human studies have demonstrated the technical feasibility and physiological effects of vestibular implants, with early signals of functional benefit. However, their role in routine clinical practice remains to be defined.

At present, clinical research in vestibular implantation has largely been confined to patients with severe bilateral vestibular failure who have coexisting sensorineural hearing loss and are undergoing cochlear implantation, typically within formal research protocols. This reflects both the recognised risk of iatrogenic hearing loss associated with inner-ear surgery and the wider ethical acceptability of adding vestibular electrodes in the context of an established surgical intervention with a well-defined risk profile.^8,9

Rather than focussing on device development alone, this narrative review synthesises current evidence on vestibular implantation with particular attention to patient selection, ethical justification and navigating implementation within publicly funded health systems such as New Zealand’s. Given the profound functional limitations, falls risk and lack of restorative treatment options, the development of vestibular implants represents a potentially important advance, not only for affected individuals but also for health systems managing an ageing population.

Methods

A narrative review of the literature was undertaken using PubMed, Embase and the Cochrane Library from database inception to June 2025. Search terms included “vestibular implant”, “vestibular neuroprosthesis” and “bilateral vestibular failure”. English-language human studies, relevant animal studies and key review articles were included. Reference lists of selected articles were manually searched for additional publications. Given the small number of clinical studies and heterogeneity in outcome measures, meta-analysis was not appropriate; thus, findings were synthesised narratively.

Ethics approval was not required as this study was based solely on published literature, not involving any human participants or identifiable data.

Clinical impact

BVF can arise from a range of aetiologies, including aminoglycoside ototoxicity, genetic vestibulopathies, autoimmune inner-ear disease and idiopathic degeneration.¹ Patients experience significant functional limitation, including imbalance, oscillopsia and reduced mobility, contributing to an increased risk of falls and substantially diminished quality of life. Vestibular rehabilitation may provide partial symptomatic relief in part of the patient population but does not restore vestibular sensory input, leaving an unmet clinical need for restorative management strategies.⁶ Importantly, BVF is associated with a markedly increased risk of falls, contributing to injury, hospitalisation and loss of independence.¹ This results in increased healthcare utilisation, as well as significant morbidity, mortality and healthcare costs.²

Rationale for vestibular implantation

The vestibular system encodes angular and linear head movements via the semicircular canals and otolith organs.⁷ These signals are transmitted through the vestibular nerve to central pathways that stabilise gaze and maintain balance. In BVF, loss of peripheral vestibular input disrupts these reflexes, notably the vestibulo-ocular reflex (VOR), resulting in blurred vision during movement.²

Vestibular implants aim to bypass damaged sensory structures by delivering patterned electrical stimulation directly to vestibular nerve branches, guided by implant motion sensor input.¹⁰ Early animal models confirmed that electrical stimulation could evoke canal-specific VOR responses.¹¹ Subsequent human prototypes, adapted from cochlear implant technology, incorporate motion sensors that detect head movement and translate this into electrical stimulation designed to mimic natural vestibular signals.¹² Functional benefit, however, depends on central adaptation to this artificial input, a process that remains less well characterised than the neural plasticity observed following cochlear implantation.¹³

In practical terms, current vestibular implant systems consist of an inertial motion sensor, an external processor and an implanted electrode array.^10,12 Head movements are detected by the sensor and converted into patterned electrical stimulation delivered to specific semicircular canal nerve branches, with the aim of recreating physiologically appropriate vestibular signals.¹¹ While conceptually analogous to cochlear implants, accurately encoding multidirectional head movement remains a complex challenge cited in the literature.¹²

Device design and surgical considerations

Vestibular implants typically use multichannel electrode arrays positioned adjacent to the ampullary nerve branches of the semicircular canals. Surgical approaches can be broadly categorised as intra-labyrinthine or extra-labyrinthine.^14,15 The former allows proximity to target nerve fibres but carries a significant risk of cochlear trauma and potential loss of residual hearing, a critical consideration given that many BVF patients retain useful auditory function.

As a result, contemporary human implantation studies have largely been restricted to patients with BVF who also meet criteria for cochlear implantation due to severe or profound sensorineural hearing loss. In this population, the incremental surgical risk associated with vestibular electrode placement is considered acceptable, as the baseline risk to residual hearing is already present and comparable to that of standard cochlear implantation.^5,9 Extra-labyrinthine methods may mitigate cochlear risk but are technically more demanding and remain less validated in human implantation.⁵

In addition to hearing risk, vestibular implantation carries potential for facial nerve injury, post-operative vertigo and device failure.¹⁴ Given that BVF is not life threatening, the threshold for acceptable surgical risk must be cautiously considered. These operative risks currently limit vestibular implantation to highly selected patients, most commonly those undergoing concurrent cochlear implantation within specialised research centres.^9,16

Clinical evidence

Initial first-in-human studies demonstrated that electrical stimulation of vestibular nerve branches could evoke canal-aligned VORs, establishing proof of concept for vestibular implants.¹⁷ Subsequent studies reported partial adaptation to continuous stimulation and improvements in measures such as dynamic visual acuity in small patient cohorts.^16,18,19 Collectively, these findings validate the basic principles that vestibular prostheses are capable of generating meaningful vestibular signals at the level of reflex physiology.

Despite measurable physiological responses, functional and patient-reported outcomes have been variable. Some participants report improved balance and reduced oscillopsia, while others report limited or no subjective benefit.¹⁸ Interpretation of these studies is limited by small sample sizes, short follow-up periods and heterogeneity in functional outcome measures, limiting the ability to draw firm conclusions regarding clinical efficacy.^12,16 To date, no large randomised controlled trials have been conducted and long-term durability of observed benefits remains unestablished.²⁰

Comparison with cochlear implantation

Vestibular implantation is often considered alongside cochlear implantation due to shared technological underpinnings.^7,14 Cochlear implants predominantly target a single sensory deficit, with well-defined functional end points such as speech perception. In contrast, vestibular implants must translate complex, multidirectional motion signals into meaningful improvements across a range of balance and functional tasks.²¹ The lack of a singular, universally accepted functional outcome measure complicates evaluating efficacy of vestibular implants and distinguishes their translational trajectory from that of cochlear devices.

Ethical and health system considerations

Ethical considerations include informed consent for experimental procedures, risks of therapeutic misconception and equitable access to specialised services. These concerns are especially relevant for patients with profound functional impairment who may be vulnerable to overly optimistic interpretations of early evidence.²² Limiting implantation to patients already undergoing cochlear implantation further strengthens the ethical justification, as the operative risks do not exceed those of an established, evidence-based intervention.⁹

In publicly funded health systems, such as New Zealand’s, cost effectiveness, resource allocation and centralisation of expertise must also be considered.²³ The existing cochlear implant programmes and otology infrastructure provide a ready framework to support the development and evaluation of vestibular implantation pathways; however, robust evidence of clinical benefit is required before scarce resources can be allocated.^23,24 These considerations must be balanced against the substantial downstream costs associated with untreated BVF, particularly fall-related injury and loss of independence.

New Zealand–specific considerations

In New Zealand, advanced otological interventions are already highly centralised, with cochlear implantation and complex lateral skull-base surgery delivered through a small number of tertiary centres.²⁵ This established infrastructure provides a practical foundation for implementing vestibular implantation into clinical practice, particularly supporting surgical expertise, peri-operative pathways, specialist audiology services and long-term device programming. However, implementation within a publicly funded health system would require careful evaluation of cost effectiveness, opportunity cost and transparent patient-selection criteria, particularly given competing demands on limited surgical and technological resources.⁹

New Zealand’s small population limits the feasibility of large single-centre clinical trials, reinforcing the importance of national co-ordination, prospective registry-based outcome collection and participation in international collaborative research networks.²⁶ As with cochlear implantation, early adoption of vestibular implants would likely need to follow a phased, evidence-generating model focussed on highly selected patients with severe bilateral vestibular loss and substantial functional impairment.²⁵

Equity considerations are central to the introduction of any high-cost implantable technology within New Zealand. Māori experience persistent and well-documented inequities in access to specialist surgical services and implantable hearing technologies, driven by geographic, socio-economic and systemic barriers.^25,27,28 Consistent with Te Tiriti o Waitangi obligations, any future vestibular implantation programme would need to embed equity-focussed design principles from the outset, including equitable referral pathways, culturally safe models of care and routine monitoring of access and outcomes by ethnicity.²⁷ Failure to address these issues risks reproducing patterns observed during the early expansion of cochlear implantation services, where inequitable uptake was documented prior to targeted policy and service redesign.^25,28

Future directions

Future research should prioritise development of validated functional outcome measures, longer-term follow-up studies and larger multicentre trials to identify patient sub-groups most likely to benefit.⁵ Technological advances, including closed-loop systems and improved signal processing, may improve outcomes. Collaboration across centres will be essential to generate sufficient evidence and guide clinical practice.

Conclusion

Vestibular implants represent a promising but still experimental approach to the management of BVF. Physiological proof of concept has been established, but consistent functional benefit remains unproven. Given current evidence and surgical risks, vestibular implantation should remain confined to specialised research settings. Further clinical trials and technological refinements are required before vestibular implants can be integrated into routine clinical practice.