Tinnitus is a complex and heterogeneous disorder associated with causing the perception of a continuous clicking, ringing, roaring, or buzzing sound (noise) in the ears in absence of any external sound source. Approximately 15% of the world’s population suffers from tinnitus, wherein 2% of these experience a substantial decrease in quality of life due to the phantom percept [1
]. Many factors associated with causing this phantom sound are still unknown, yet, it is often associated with an underlying damage in the ear, such as the loss of cochlear hair cells. The loss of the hair cells can have different origins: a common risk factor is an acoustic trauma (exposure to loud sounds), the same applies to ototoxic drugs. However, tinnitus can also develop as a symptom of a cochlear affecting disease, such as Ménière’s disease (MD), or in the course of aging and age-related hearing loss (presbycusis) [2
]. Age-related physiologic changes, for example, degeneration of sensory receptor cells, are one common cause of disorders of the sensory systems, like the auditory system [4
]. Further age-related changes have been identified in auditory processing in the brain and may be related to the generation of dementia [5
]. Besides the increased risk of tinnitus with higher age, elder persons have also been shown to experience more tinnitus-related distress which is theorized to be related to decreased compensatory brain plasticity [7
]. In a steadily aging society, presbycusis and tinnitus thus become more prevalent with consequences beyond auditory sensory handicaps.
Presently, tinnitus is considered as a condition that involves changes at different levels of the auditory pathway, the auditory cortex as well as non-auditory areas like the limbic system. These changes may additionally be influenced by psycho-social stress (for example, negative thoughts, the argument at home, increased workload, etc.), affecting the emotional status and the auditory system [8
]. Consequently, variations in tinnitus loudness and tinnitus-related distress, as well as the individual perception of tinnitus has been often reported by tinnitus patients [10
]. Additionally, tinnitus variations can be directly or indirectly affected by changes in the atmospheric surrounding [11
] and environmental conditions of the patient [12
]. Individual case studies on weather conditions and their impact on fluctuations in tinnitus show limited but some evidence of a connection [13
]. In patients suffering from MD [15
], which commonly occurs with hyperacusis [16
], a weather change usually contributes to tinnitus increase [18
]. Abrupt change in barometric pressure (particularly reduced pressure) may cause or increase tinnitus symptoms because it affects the eardrum, the round window, and the cochlear fluids. Increased wind speed or humidity also worsen the tinnitus symptoms due to influences of high sensitivity on the ears [12
]. A similar relationship applies to seasonal change [19
Smartphone-based Ecological Momentary Assessments (EMA) methods can be utilized to capture the variations in tinnitus perception and link them to current surrounding or environmental conditions of the patient [20
]. Furthermore, the tinnitus variations related to stress can be coped with using smartphone-based Cognitive Behavioural Therapy (CBT) or self-help apps, and individual perception of tinnitus can be managed using smartphone-based tinnitus relief apps. Despite smartphones, smartphone apps, and auxiliary health devices, for instance, heart meters, activity trackers, and smart wristbands, have become popular in assisting patients in managing and controlling their health problems [21
], further research to determine the effectiveness of these applications and devices in different domains of healthcare is still required [23
]. Nonetheless, smartphones are interesting in particular as most of today’s smartphones provide high computational power, a long-lasting battery life, and incorporate a set of sophisticated built-in sensors that are capable of accurately monitoring environmental surroundings and can be programmed and managed by apps. Additionally, smartphones provide an application ecosystem, extendable to program and include new apps targeting different health problems at almost negligible costs. New smartphone apps can be designed or existing apps can be tailored to assist in managing or mitigating the symptoms of different health problems [25
]. For instance, mobile crowdsensing and smartphone-app solutions can be applied to monitor the ecological or environmental surroundings of patients using the built-in sensors [26
]. Similarly, for tinnitus, these smartphone-app–based solutions also apply. However, due to the fast-growing development and the continuous publishing and inclusion of new apps in the app market places, the current state of smartphone apps within the context of tinnitus is mostly unbeknownst to patients and clinicians alike.
In this paper, based on the PRISMA guidelines [28
], we explore online scientific literature sources namely: Google Scholar, CiteSeerX, Microsoft Academics, and Semantic Scholar as well as app stores, namely: Google’s Play Store and Apple’s App Store to list and identify tinnitus-related smartphone apps. The idea of this paper is to list and index smartphone-based solutions for assisting patients suffering from tinnitus, to foster a better understanding, management and treatment (by the provision of therapeutic solutions), as well as monitoring the severity of their tinnitus. Likewise, we report on apps that succor tinnitus patients in testing for hearing impairment (usually accompanied by tinnitus [29
]), and, if possible, protect and train the remaining hearing abilities.
A review by Sereda et al. [30
] lists tinnitus management apps based on patient opinions, gathered via a web-based survey. Moreover, the apps identified through a web-based patient survey are further evaluated based on the Mobile Application Ratings Scale (MARS) [31
]. The added value from our review is primarily the exploration of the smartphone app markets to reveal relevant apps, as opposed to using a survey. The review by Kalle et al. [32
] discusses internet- or smartphone-delivered CBT, with particular focus on self-help for tinnitus. The authors demonstrate the role of several approaches in advancing tinnitus clinical practice, but have focused less on current and available apps for patients. The review by Lui et al. [33
] addresses efficacy or effectiveness of mental-health-app–based therapeutic solutions, but not with a particular focus on tinnitus. However, they do consider apps based on CBT, one of the most common therapies in the tinnitus domain. In our review, we do not limit the scope to CBT, self-help, or mindfulness apps, rather we expand further to address apps that also fall into the non-therapeutic category. In another article [34
], the authors have outlined hearing healthcare apps from prominent smartphone platforms. However, the list of apps is limited and most apps have been outdated. Similarly, Bright and Pallawela [35
] discuss smartphone apps for hearing assessments including comparison and validation of apps. In comparison, the scope of our proposed work is not limited to hearing assessments, but further includes additional apps for hearing healthcare, for instance, hearing protection and enhancement apps.
In summary, unlike the aforementioned studies and reviews, the objective of the presented review is to identify and report on smartphone-based solutions (apps specifically), within the context of tinnitus, that are, in turn, widely and easily available on mainstream app stores. Additionally, a further objective is to report on the current state of smartphone-based app solutions presented in the literature, be that either in the form of discussing the underlying technology or technique used for the development of the smartphone app, or the effectiveness of the smartphone apps for tinnitus patients. The overall process of identification of smartphone apps on scientific literature sources as well as on app store markets is detailed in Section 2
. The identified results are reported and discussed in Section 3
. Before concluding the article, the limitations and potential directions of proposed reviews are reported in Section 4
4. Limitations, Future Work and Conclusions
Relevant literature search—we are aware that keyword-based search can have limited coverage, because there may be relevant documents not matching the chosen keywords. Different search results obtained by the same query terms applied on different data sources gave some hints that query terms could be further optimized. We attempted to improve this by isolating keywords that caused reduced recall, however, we believe that it can be further improved. Similarly, most of these searches were performed using the keyword ‘tinnitus’, this, on one hand, increases the precision to find tinnitus-related studies, however, on the other, it limits the identification of studies reporting on closely related subject areas to tinnitus. For instance, adding the ‘hearing loss’ keyword in the search criteria could benefit from increasing the recall. Furthermore, we thoroughly ensured the selection of relevant literature based on primarily investigating the abstract and introduction for relevance, and secondarily based on the content of the paper. Again, we are aware that this process is subjective and can probably be further improved.
Identifying relevant apps—another limitation of our proposed work constitutes the restricted search of relevant apps in only two app stores, namely Google’s Play Store and Apple’s App Store. Even though we justify this restriction, there is a slight chance that our work could benefit by exploring other app stores, like Amazon’s and Samsung’s app stores. Although unlikely, 3rd party independent app stores like Aptoide or F-Droid may contain previously unseen apps. During our searches, we identified apps which were relevant for this review and were part of Google’s Play Store or Apple’s App Store at one point of time, however, they were removed from respective app stores due to policy conformation issues. Usually, removal of an app from these app stores is properly justified, however, these restrictions can sometimes be inconsistent. Furthermore, to include an app in this review, we inspected the app description and a selection of a few top-rated comments from users. This approach is subjective and highly relies on the knowledge of the inspector about the domain and can be further improved by collecting opinions from domain experts as opposed to general users.
For prospective work, we primarily aim to extend our work by reviewing internet- and computer-based behavioral therapies applied directly in the context of tinnitus research. Herein, an additional focus would be to include studies that report on the use of auxiliary and peripheral sensors in assisting therapeutical solutions. For instance, the use of smartwatches or wristbands to acquire physiological attributes of patients suffering from tinnitus could be additionally included. Secondarily, as future work, we plan to extend our work by addressing psychological conditions that are closely related to tinnitus. In view of this, the objectives of the study would be to identify smartphone-based solutions, as well as internet- and computer-based therapeutical solutions offered for the said complications. Furthermore, the study will report on the importance of highlighted therapies and opinions of smartphone-based solutions from the perspective of patients.
In conclusion, the review presented in this paper highlights the impact of mobile applications and mobile crowdsensing platforms, specifically within the context of tinnitus research. We identified and investigated a wide array of heterogeneous apps heavily invested in supporting and controlling tinnitus symptoms, understanding tinnitus, and monitoring patients suffering from tinnitus. Primarily, we highlighted the available mobile apps that could be beneficial for a patient in mitigating or masking annoying phantom sounds. We further explored different smartphone-delivered CBT therapies that can be adopted by tinnitus patients to manage stress and anxiety accompanied by tinnitus. As significant and continuous exposures to dangerous levels of sound are critical aspects in increasing tinnitus symptoms or causing them, secondarily, we scrutinized mobile apps that are helpful in monitoring noise levels and noise exposure, including apps that notify the user of dangerous exposure. Moreover, we inspected apps that are useful in testing hearing. This is beneficial for patients suffering from tinnitus by allowing them to monitor the hearing loss commonly occurring with tinnitus. Furthermore, we explored and presented apps that provide assistance to patients suffering from hearing impairment. For all categories, we not only provided a list of available apps but also reviewed relevant literature documenting the usage and role of those apps.