Tech Topic | April 2020 Hearing Review

By Drew Dundas, PhD, and Suzanne Carr Levy, PhD

In January 2019, the FDA approved a new and  improved inductive radio power system for the Earlens Contact Hearing Solution which replaced the previous light-driven system. This article details the advantages of this change, and provides study results on the benefits of the inductive coupling system and how it is equal to or surpasses the light-driven system in several parameters.

The next-generation Earlens Contact Hearing Solution was cleared for market distribution by the FDA in January 2019. This is the second in the class of Tympanic Membrane Contact Hearing Aids; the predicate was the Earlens Light-Driven Contact Hearing Aid. 

The basic mechanisms of action and performance characteristics of the two systems are identical: they both provide broad-spectrum amplification extending from 100 Hz to 10 kHz for the target population of users with SNHL, within the mild-to-severe ranges. While the sensitivity to alignment between the laser emitter in the Light Tip and the Photodetector on the lens resulted in undesirable output variability with normal facial movements in the Light-Driven system, the Contact hearing solution with Inductive coupling is much more resilient to these same variations. This article reviews the results from a comparative study that demonstrates the superior bandwidth performance of the Earlens Light-Driven System is maintained in the Inductive Earlens Contact Hearing Solution, and that the consistency of maximum output is, in fact,  improved due to the consistency of coupling between the Inductive Ear Tip and Lens. 

Technology Comparison

The Light-Driven and Inductive systems are both contact hearing devices intended for the treatment of mild to severe sensorineural hearing impairment. Both systems are comprised of five key components: 1) A rechargeable, behind-the-ear processor; 2) Custom Ear Tip; 3) Custom Tympanic Lens; 4) Wireless charger, and 4) the Earlens Control app for iOS devices (see top illustrations in Figure 1). Similarly, both systems provide superior audible bandwidth and stable gain, which when combined with the direct drive modality, results in superior sound quality performance and enhanced speech understanding performance by providing access to high- frequency speech information without occluding the ear. 

Figure 1. Illustrations of Light-Driven and Inductive Earlens systems. Bottom graphs: Comparative system sensitivity to transmitter position including offset variation and angular rotation illustrating the reduced sensitivity of inductive coupling to output variability (dB power loss).

Sound is digitally processed in a state-of- the-art, behind-the-ear processor, and signal and power are transmitted wirelessly from the Ear Tip Emitter to the Tympanic Lens. The Lens receives the power and signal, and drives a receiver-like motor that makes contact with the umbo of the malleus on the surface of the tympanic membrane, transmitting vibratory energy to the cochlea via the ossicular chain. (For a detailed overview of Earlens system function, see Dundas and Levy1and Gantz et al.2)

The Inductive system differs from the previous Earlens Light-Driven Hearing Aid only in terms of the method of energy and data transmission, replacing the infrared laser light link with the resonant inductive radio link (top right illustration in Figure 1). This method of transmission drastically reduces the sensitivity to misalignment between the Ear Tip and Tympanic Lens components (bottom graph comparisons in Figure 1) and increases the predictability and efficiency of the system. 

Comparative Performance Data

A total of 48 adult existing Earlens Light-Driven Hearing Aid users who met the indications for use consented to participate in an IRB-approved human factors study and received study devices incorporating the Inductive system. All participants completed activities in the study protocol that were consistent with the standard of care. Basic performance measures of each system were conducted, and participants completed subjective questionnaires intended to address key study questions. 

Results and Discussion

Subjective assessment of sound variability. Sound variability, or the perception of volume fluctuation with jaw or facial movements, affected about 20% of Light-Driven or Photonic Earlens users. Although not pervasive, it represented a noticeable indicator of misalignment due to ear canal dynamics. 

Sound variability was expected to be virtually eliminated with the change to the inductive link, and responses to the questionnaires administered confirmed this prediction (Figure 2). In the few individuals who reported a worsening of sound variability with the Inductive system, the root cause was traced to lateral migration of the Ear Tip, a common fit-related problem that can occur with acoustic aids as well.

Figure 2. Participant ratings of comparative sound variability with the Inductive vs Light-Driven Earlens systems for n=33 participants.

Unaided and aided sound-field testing. Earlens employs a CAM2-based3 fitting algorithm to prescribe gain based on the user’s audiometric thresholds. Paired comparisons of unaided and aided threshold data in both device conditions (Photonic and Inductive) were obtained for 43 ears and mean data are shown in Figure 3. Standard deviations of the mean aided thresholds ranged from 6 to 14 dB across tested frequencies. The mean difference between the thresholds obtained with the two systems across frequencies was 1.2 dB, a clinically insignificant change. 

Figure 3. Average unaided headphone (grey) and aided sound field threshold values for the Light-Driven (orange) and Inductive (blue) systems.

Results showed that functional audibility was achieved in the frequency range from 250-10,000 Hz as appropriate for the indicated fitting range. Thus, the broad-spectrum amplification that underlies the basis for the sound quality of the Light-Driven system was maintained in the Inductive system. 

Word recognition testing. Word recognition was tested at a soft conversational level (45 dB HL) in order to eliminate ceiling effects in the scores. The results for 41 ears with data in all three conditions are shown in Figure 4 for unaided, the Photonic system, and the Inductive system test conditions. The Photonic and Inductive system produced similar average results, as expected. 

Figure 4. Average word recognition scores (at soft conversational level, in quiet) for unaided (grey), for the Light-Driven Photonic (orange), and the Inductive (blue) systems.

Maximum Output. The maximum output of the system is an indicator of system performance. Misalignment of the Light-Driven signal results in lower maximum output due to reduced efficiency of energy transfer. Reduced available “headroom” can limit potential benefit in louder and more complex listening environments. 

Maximum output was extracted from fitting files and compared for the Light-Driven and Inductive systems. Figure 5 shows comparative data indicating maximum output was higher for the Inductive system due to reduced sensitivity to misalignment, which leads to more predictable fitting outcomes for the clinicians.

Figure 5. Mean and standard error of maximum output obtained in n=56 ears for inductive (blue) and light-driven (orange) Earlens Systems.

Safety and adverse events. The safety of the device was monitored as per the standard of care. There were no unanticipated adverse events and no serious adverse events. The rate, severity, and frequency of the adverse events seen were comparable to those encountered with the Photonic system and other hearing aids. 

Discussion and Conclusions

With the Earlens Contact Hearing Solution with inductive coupling, the expected human factors benefit associated with the reduction in sound variability and misalignment were confirmed and aided gain and word recognition testing results provided confirmatory evidence that the effectiveness of the amplification of the Earlens Contact Hearing Solution was maintained regardless of method of energy transmission. 

For the Inductive system, the maximum output was less susceptible to misalignment than the Light-Driven system, yielding a more predictable experience for the patient and the clinician and fewer Ear Tip remakes. The safety profile of the Inductive technology was consistent with the Light-Driven Earlens system.

The Earlens Contact Hearing Solution with Inductive coupling has effectively eliminated major challenges associated with the Light-Based Earlens system, while maintaining the same safety profile and functional benefit for users and is currently on the market in select locations across the United States.

Correspondence can be addressed to HR or Dr Levy at: Suzanne.Levy@earlens.com 

Original citation for this article: Dundas D Levy SC. Earlens Contact Hearing Solution introduced with inductive coupling vs light-driven coupling. Hearing Review. 2020;27(4):28-30.

References

1. Dundas D, Levy SC. The Earlens Light-Driven Hearing Aid: Top 10 questions and answers. Hearing Review. 2018;25(2):36-39. 

2. Gantz BJ, Perkins R, Murray M, Levy SC, Puria S. Light-driven contact hearing aid for broad-spectrum amplification: Safety and effectiveness pivotal study. Otol Neurotol.2017;38(3):352-359.

3. Moore BCJ, Glasberg BR, Stone MA. Development of a new method for deriving initial fittings for hearing aids with multi-channel compression: CAMEQ2-HFInt J Audiol.2010;49(3):216-227.