Hypothesis: That maximum equivalent pressure output (MEPO) and maximum stable gain (MSG) measurements demonstrate high output and high gain margins in a light-driven hearing system (Earlens).
Background: The nonsurgical Earlens consists of a light-activated balanced-armature transducer placed on the tympanic membrane (Lens) to drive the middle ear through direct umbo contact. The Lens is driven and powered by encoded pulses of light. In comparison to conventional hearing aids, the Earlens is designed to provide higher levels of output over a broader frequency range, with a significantly higher MSG. MEPO provides an important fitting guideline.
Methods: Four fresh human cadaveric temporal bones were used to measure MEPO directly. To calculate MEPO and MSG, we measured the pressure close to the eardrum and the stapes velocity, for sound drive and light drive using the Earlens.
Results: The baseline sound-driven measurements are consistent with previous reports. The average MEPO (n = 4) varies from 116 to 128 dB SPL in the 0.7 to 10 kHz range, with the peak occurring at 7.6 kHz. From 0.1 to 0.7 kHz, it varies from 83 to 121 dB SPL. For the average MSG, a broad minimum of about 10 dB occurs in the 1 to 4 kHz range, above which it rises as high as 42 dB at 7.6 kHz. From 0.2 to 1 kHz, the MSG decreases linearly from approximately 40 dB to 10 dB.
Conclusion: With high output and high gain margins, the Earlens may offer broader-spectrum amplification for treatment of mild-to-severe hearing impairment.