In 2013, an estimation by the World Health Organisation (WHO) indicated that over 5% of the world’s population suffers from disabling hearing loss. This may seem like a small figure, however, it amounts to approximately 360 million people across the globe. Many of those affected by hearing loss live in low and middle income countries where hearing healthcare services are not always readily available. The lack of hearing healthcare services isn’t a burden on developing nations alone. During World Hearing Day this year (2018), WHO estimated that 900 million people will suffer from disabling hearing loss by 2050. It’s evident that hearing loss has become a global healthcare epidemic and its long term effects are a burden on individuals, families and communities as a whole. The lack of hearing health care professionals and quality audiological equipment only aggravates this problem, worsening the effects it has on those already affected.
Recent advances in smartphone technology applications has allowed for the creation of various smartphone-based audiometer applications aimed at tackling this growing challenge. Allowing for the provision hearing healthcare services even in underserved regions like sub-Saharan Africa. Before we take a deeper look into smartphone-based audiometry, it is important to distinguish between the different types of audiometers currently available on the market. outside of a soundbooth, the KUDUwave audiometer (which does not require a sound booth) and finally smartphone-or tablet- based audiometers.
A smartphone-based audiometer is an application loaded onto a smartphone, this application simulates an audiometer - by presenting different intensity tones across the frequency spectrum. Generally, supra-aural headphones (i.e. Sennheiser HD 202 II) are used as a transducer with smartphone-based audiometers. Mobile audiometer applications have gained much attention recently, particularly in school-based screenings. These audiometers promise to bridge the gap of hearing healthcare service delivery by allowing access to early hearing loss detection.
Smartphone-based audiometers have emerged as possible means of providing audiological services. However, what needs to be discussed is exactly where they fit in the field of audiology.
Accuracy & Validity of smartphone-based audiometers
Various studies have assessed the accuracy and validity of pure tone air-conduction testing using smartphone-based audiometers as compared to conventional audiometers. These studies have been conducted in waiting rooms, quiet offices and sound booth environments. In some cases, smartphone-based audiometry has been found to correlate with conventional audiometry and in others cases not. Certain authors concluded that the applications are better used for end-user screening than clinical application. In contrast, some studies found that thresholds produced by smartphone-based audiometry correlate with conventional audiometry within 10 dB. Does this then suggest that smartphone-based audiometers may be used for diagnostics purposes in audiology? Let’s dig deeper into this.
Hearing threshold variation of 10 dB or less, between the smartphone-based and the conventional audiometer is acceptable as sub-clinical within the context of clinical diagnostic audiometry. It should be noted that, in some instances, for example with children and ototoxicity monitoring cases, a difference of 10 dB could be significant.
Study evidence indicates that the accuracy of smartphone-based audiometers is heavily affected by the testing environment. This is indeed crucial with regards to clinical application, as an ideal sound booth environment isn’t always possible.
Clinical implications
The big question is, where do smartphone-based audiometers fit in?
To sum things up, they cannot substitute or match up to the accuracy of standard audiometry testing done by a qualified audiologist. Nonetheless, they can be used for screening, especially in settings with limited resources. Some may argue ‘’...the results from other studies show thresholds comparable to standard audiometry, so why not use them in clinical applications?’ While that statement holds true, here is why I think it should be limited to screening for the time being; 1) It may produce inaccurate results, particularly for low frequencies. Ambient noise results in elevated hearing thresholds, more especially the lower frequencies. As you know, inaccurate results lead to wrong referrals, waste of money and mismanagement (i.e. unnecessary hearing aid fitment). It is advised that smartphone-based audiometers be used in a soundbooth or in a very quiet room, as the commercial earphones or supra-aural/circumaural headphones do not attenuate ambient noise sufficiently. 2) In general, smartphone-based audiometers are not able to distinguish between conductive and sensorineural hearing loss. This feature is key in the diagnosis and management of auditory disorders. But after all, this isn’t written in stone, it is subject to change. But one can only speak of the current data available right now.
Could Helping Hurt?
A lot of Non-Government Organisations (NGOs) mean well. But at times, hearing healthcare services provided by NGOs may be severely harmful to those on the receiving end. I can recall a colleague of mine, a qualified audiologist, telling me about an audiology outreach done with a NGO. A smartphone-based audiometer was used to assess 30 adults in an open hall (which definitely was not quiet enough), supra-aural earphones were used to present air conduction pure tones to the participants. Twelve (12) of these adults had, at least, moderate hearing loss according to the data on the audiometer. Two weeks after the outreach, hearing aids were programmed at a hearing aid distribution head office, then sent back to the community for fitting. Now, what is wrong with the above course of events? Didn’t the NGO just help people? No, the help provided possibly hurt the patients. In my professional opinion, a full diagnostic assessment should’ve been properly conducted in order to plan and manage patients accurately and safely. The results from the smartphone-based audiometers could have easily been elevated because of the ambient noise levels in the test room, thus, leading to incorrect hearing aid fitting and overamplification. Furthermore, the individuals could have a conductive hearing loss, and would have been appropriately assisted by referral for medical management.
Recommended clinical applications for smartphone-based audiometers