King Chung
Background/Objective: One of the missions of the United States FDA is "protecting the public health by ensuring the safety, efficacy, and security of human and veterinary drugs, biological products." The current guidelines for OTC hearing aids impose an output limit of 111 dB SPL for linear hearing aids and 117 dB SPL for compression hearing aids when measured using 90 dB SPL pure tones in a 2 cc coupler. This means that the sound pressure level at the ear drum at a frequency would be 111 or 117 dB SPL plus the real-ear-to-coupler difference (RECD) of the 2 cc coupler at the frequency. Methods: The maximum aidable hearing thresholds by hypothetical OTC-compression hearing aids that are compliant with the current FDA guidelines were explored using NAL-NL2 and DSLv5 prescriptive methods. The theoretical maximum permissible overall output levels in the ear canal were also calculated. Additionally, the fitting range of OTC-compression hearing aids with a maximum of 117 dB SPL output level at the ear drum was explored. Results: The current FDA guidelines allow OTC-compression hearing aids to provide sufficient gain and headroom to fit individuals with severe to profound hearing loss. In the presence of a loud wideband signal, the maximum overall output level can reach 164.5 dB SPL in the ear canal for an OTC-compression hearing aid with a bandwidth of 5657 Hz. When the maximum output levels are defined at the ear drum (i.e., the RECD is already considered), however, the fitting range is lowered to moderate hearing loss and the maximum overall output level is lowered by 10 dB. Conclusions: These findings identified potential regulatory vulnerability in the current FDA guidelines and suggest the need to take the measurement coupler and its corresponding RECDs into account when setting the guidelines for OTC hearing aids. Other alternative strategies to prevent potential abuses of the guidelines are also discussed.