|Year : 2016 | Volume
| Issue : 1 | Page : 8-14
Hearing and audiometric estimates in a blind population in North-Western, Nigeria
Abdulazeez Ahmed1, Emmanuel Raphael Abah2, Kehinde K Oladigbolu2
1 Department of Otorhinolaryngology, Faculty of Clinical Sciences, College of Health Sciences, Bayero University/Aminu Kano Teaching Hospital, Kano, Nigeria
2 Department of Ophthalmology, Ahmadu Bello University Teaching Hospital, Shika, Zaria, Nigeria
|Date of Submission||24-Jul-2015|
|Date of Acceptance||03-Feb-2016|
|Date of Web Publication||12-Feb-2016|
Department of Otolaryngology, Faculty of Clinical Sciences, Bayero University/Aminu Kano Teaching Hospital, Kano
Background: In our environment there is lack of awareness about the specific effects that hearing loss has on a blind person. The early identification of deafness and its early treatment have clearly been shown to lead to significant improvements in a child's social and educational achievement. There is also evidence that comprehensive examination of students in boarding schools usually leads to rapid identification of conditions predisposing or associated with preventable ear diseases. Objective: This study aims to estimate prevalence of hearing impairment and other otological problems among blind students in Kaduna State special education school. Subjects and Methods: All consenting, consecutive students were recruited and assessed using the WHO Ear and Hearing disorders survey protocol. Otoscopy and audiometric air conduction thresholds were established separately for the left and right ear of each subject respectively, using frequencies of 500, 1000, 2000, and 4000Hz to estimate mean hearing thresholds. Results: A total of 58 students were recruited for this study with a prevalence of hearing impairment of 17.2%. The age of the students ranged from 10 to 25years with a mean age of 15.53years (SD: 3.3years). There were 22 (37.9%) females. Pure Tone Audiometry for the right ear revealed a minimum hearing threshold of 15dBHL and maximum of 83.75dBHL, with a mean hearing threshold of 22.03dBHL (SD: 1.20). Similarly, the left ear had a minimum threshold of 12.50dB and a maximum of 28.75dBHL, with a mean of 20.50dBHL (SD: 0.40). Five students (8.6%) had unilateral hearing impairment of variable severity. Cerumen auris (wax) was the commonest 18 (31%) otologic disorder. Conclusion: Efforts are needed toward strengthening hearing screening with provision of hearing aids for the institutionalized blind or persons with dual disabilities.
Keywords: Blind students, hearing loss, otologic diseases, wax
|How to cite this article:|
Ahmed A, Abah ER, Oladigbolu KK. Hearing and audiometric estimates in a blind population in North-Western, Nigeria. Sub-Saharan Afr J Med 2016;3:8-14
|How to cite this URL:|
Ahmed A, Abah ER, Oladigbolu KK. Hearing and audiometric estimates in a blind population in North-Western, Nigeria. Sub-Saharan Afr J Med [serial online] 2016 [cited 2019 Oct 16];3:8-14. Available from: http://www.ssajm.org/text.asp?2016/3/1/8/176294
| Introduction|| |
In many instances, there is a lack of awareness about the specific effects that hearing loss has on a blind person. The early identification of deafness and its early treatment have clearly been shown to lead to significant improvements in a child's social and educational achievement.  There is evidence that comprehensive examination of students in boarding schools usually leads to rapid identification of conditions predisposing or associated with preventable ear diseases. 
Several studies have demonstrated that hearing and vision impairments significantly influence the activities of daily living (ADL), which refers to daily self-care activities such as dressing, eating, and personal hygiene, and the instrumental ADL (IADL), which refers to activities such as using the telephone, managing money, doing housework, and shopping. , Furthermore, both hearing and visual impairments increase the risk of falls, and fear of falling can lead to general uncertainty, dependency, feeling unsafe, reduced social participation, and difficulties carrying out daily activities (participation restriction). There is evidence linking hearing sensitivity and blindness, a kind of neural reorganization, for example, if one loses a sense the area of the brain normally devoted to that sensory information is reorganized and put to work processing other senses. This was initially hypothesized by Niemeyer and Starlinger, as the better utilization of auditory information after the loss of visual information channel of the brain.  This phenomenon of the brain reorganizing itself to support and augment other special senses is called cross-modal neuroplasticity.  Understanding this process has implications for rehabilitation of the deafblind but at the same time, we need to be able to identify/quantify the burden of dual sensory impairment (deafblind) especially in resource-poor settings such as ours.
The prevalence of "any" type of hearing impairment in normal school-going persons in sub-Saharan Africa ranges from as low as 0.9% in southern Africa to as high as 13.9% in Nigeria. , In contrast, other studies estimate that in developing countries, prevalences can range from 6% to 15%. , Prevalence of deafness and hearing health estimates in special populations such as blind individuals are scarce. Conversely, the prevalence of ocular anomalies in deaf students is 20.9%.  Furthermore, congenitally deafblind children often suffer from multiple cognitive and neurological disorders, such children with a congenital cause of dual sensory impairment are usually sent to institutions for cognitive impaired/physically challenged children (Torrey Home). Occasionally, deafblind children are hurriedly placed in these schools because of a dire need to take the child out of their immediate environment (for fear of stigmatization) or for educational purposes or both. Knowledge of the impact and degree/severity of hearing loss among these children can go a long way in reducing the stigma attached to these disabilities and help to place them into the appropriate educational environments.
To our knowledge, there has not been any study highlighting the prevalence estimates and causes of hearing loss or impairment in a blind school in North-Western Nigeria. Some of the most common causes of hearing loss in Nigeria are measles, mumps, meningitis, and rubella (also a known cause of dual disability). In the past, some authors have reported rubella antibodies in pregnant women in Southwestern Nigeria; this may ultimately place their unborn children at risk of congenital rubella syndrome (CRS). , In a deaf school study from north central Nigeria, it was hypothesized that rubella may be responsible for as much as 1.5-2% of childhood deafness.  Similarly, hearing loss in deafblind persons may also be "idiopathic," various vascular hypothesis have been reported in the causation of this dual disability. 
Based on World Health Organization (WHO) classification for clinically confirmed CRS case, deaf children with rubella retinopathy may be adjudged to have CRS and children with cataracts/aphakia or congenital glaucoma with undetected hearing loss may also be assumed to have CRS. 
Other causes of hearing impairment common in Nigeria include; Ear diseases such as otitis media, otitis externa, cerumen auris, foreign bodies; hereditary/genetic causes; noninfectious causes and sometimes causes are unknown. Among children and adults, cerumen auris (wax) ranks highest as a major contributor of hearing impairment due largely to ear diseases. This applies to both deaf and normal children. , However, no such studies are available for the institutionalized blind in our environment. It cannot be overemphasized that routine ophthalmological and otorhinolaryngological screening will go a long way in helping these cohorts to have better education and social adjustment.
Therefore, this study aims to estimate the prevalence of hearing impairment and report otologic problems among blind students in Kaduna State Special Education School, which provides primary and secondary education for nearby states.
| Subjects and Methods|| |
This was a descriptive cross-sectional survey of blind students in a boarding facility in Kaduna States Special School, Kaduna-Nigeria. This school in addition to four other special schools for the deaf, blind, and physically challenged children serves the region and run by either government, private or nongovernmental agencies. This particular school was selected by simple random sampling (ballot).
Two teachers were constantly on the ground to help with filling of questionnaires, testing and to give confidence to the students. The WHO ear and hearing disorders survey protocol was utilized to document data such as demographic data, basic ear assessment, duration of hearing impairment, family history of hearing loss, audiometric data, causes of ear disease and/or hearing impairment and whether or not any action is needed and the type of intervention.
The study was conducted within 10 days (January 26 to February 06, 2013). Hearing impairment was based on WHO criteria: 25 dB or less normal hearing, 26-40 dB mild hearing loss, 41-60 dB moderate hearing loss, 61-80 dB severe hearing loss, and ≥81 dB is considered profound hearing loss. While disabling hearing loss (DHL) refers to hearing loss >40 dB in the better hearing ear in adults (15 years or older) and >30 dB in the better hearing ear in children (0-14 years) of age. 
A Kamplex Diagnostic Audiometer AD17 with TDH 39 headphones calibrated prior to testing day was used and a biological check was performed on each day. This biologic check involves testing, at least, two persons with known stable hearing thresholds each day to make sure there are no baseline threshold changes in the audiometer. Pure-tone audiometry (PTA) was conducted in accordance with the modified Hughson-Westlake ascending technique. Audiometric air conduction thresholds were established separately for the left and right ear of each subject respectively, as recommended by WHO, which requires the establishment of sensitivity at frequencies of 500, 1000, 2000, and 4000 Hz to estimate average hearing thresholds. The pure-tone average (PTAv) is the average value at these frequencies based on hearing scores of the participants' better ear. The severity of hearing impairment and thus DHL was categorized using the PTA score.
Hearing testing was performed by two trained audiometricians, while otoscopy and eye examination were performed by the otolaryngologist (using a Heine Mini 3000 ® Otoscope) (Heine mini 3000 pocket otoscope) and ophthalmologist (using a Snellen chart, ophthalmoscope, and loupe), respectively. Bone conduction assessment and tympanometry was not carried out in this survey, however, for the purpose of identifying otitis media with effusion (OME), students with intact but thickened, dull/opalescent tympanic membranes or tympanic membranes with increased vascularity with or without fluid levels were tentatively labeled as OME. In addition, this was confirmed with a 512 Hz tuning fork using a "negative Rinne's test" to confirm this and a Weber's test to confirm laterality, bearing a mind false positive and negative tests.
None of the students was observed using a hearing aid. Students who required further investigation or care were promptly referred following a prearranged preferential treatment protocol at the health facility. Nonparticipation by some of the students was due to fear and apprehension of the transducer covering the ears and of the entire audiometric device while most were absent from school during the period of the survey.
Ethical clearance was obtained from the State Ministry of Education. Permission and Consent were obtained from the schools' principal and pure-tone audiometry (PTA). Assent was obtained from the students who were <15 years and consent from those equal to or above this age.
This study was conducted according to the ethical principles of the World Medical Assembly revised Declaration of Helsinki (2013).
IBM SPSS statistic (for windows, version 20) software was used to analyze generated data. Descriptive statistics using Excel was used to examine demographic data and hearing ability at different frequencies. Chi-square (tested) crosstabs, was used to explore the relationship between categorical variables while a Wilcoxon signed ranks test for related measures was used to assess difference in the median score for pure-tone thresholds of both ears.
| Results|| |
A total of 91 students attend the special school for the blind in Kaduna state; 58 of them consented for this study giving a participation rate of 63.8%. The prevalence of hearing impairment in this cohort is estimated to be 8.6%. The age of the students ranged from 10 to 25 years with a mean age of 15.5 years (standard deviation [SD]: 3.3 years); females were 22 (37.9%) and males 36 (62.1%). No student <14 years was identified with DHL using WHO criteria, but 1 (4.3%) student had a mild hearing impairment while 2 (5.8%) adults (≥15 years) had disabling hearing impairment [Table 1]. Regarding PTAv in the right ear; the minimum hearing threshold is 15.00dB and maximum of 83.75 dB, with a mean hearing threshold of 22.03 dB (SD: 1.20). While PTAv in the left ear revealed a minimum threshold of 12.50 dB and a maximum of 28.75 dB, with a mean of 20.50 dB (SD: 0.40).
Test to compare the median between the left and right ear hearing thresholds in this cohort revealed no statistically significant difference in the median of both right and left thresholds of hearing (Z = −0.529, P = 0.597). Five students (8.6%) had significant unilateral hearing impairment of variable severity; however, a total of 6 (10.4%) students had asymmetric hearing impairments [Figure 1]. With respect to better ear frequency-specific thresholds, 500 Hz was found to have the highest number of participants 11 (19%) with reduced hearing thresholds at the 90 th percentile while 3 (5.2%) were above the 90 th percentile.
No data could be reported for the duration of hearing loss, family history or relative of a participant having difficulty hearing because those affected did not realize they had a hearing impairment. Some others could not recall history pertaining to these questions following the WHO ear and hearing disorder survey protocol, so getting reliable data in this regard was futile. Multivariate regression analysis did not yield any significant predictors for hearing loss in our study (P = 0.467 and odds ratio: 1.09).
With regard to otologic problems in this cohort, cerumen auris (wax) was the most common 18 (31%), then OME with 4 (6.9%), while chronic suppurative otitis media (CSOM) and otomycosis were 1 (1.7%), respectively. Thirty-four students (58.6%) had normal otoscopic findings [Figure 2].
| Discussion|| |
This study was able to discern that blind students are also prone to problems of hearing acuity as well as ear diseases. The prevalence of hearing impairment realized in this study was largely due to asymmetric hearing losses where the majority were male students. 11.5% of the affected age category presented with varying degrees of hearing impairment from mild to profound.
In a screening survey, among a Dutch institutionalized population of 672 people (with mild to profound intellectual disability) for hearing and visual function, they recorded a prevalence of hearing impairment of 21%.  In comparison to our prevalence, this is quite high, both prevalences highlight the fact that special populations such as ours, do have problems with hearing requiring attention and/or evaluation.
Conversely, in a study among normal school children for hearing impairment in an inner city area of Lagos, Southwestern Nigeria, 13.9% was reported which is more than our finding.  Our lower prevalence estimate may be due to lack of representative sample size for deafblind persons since many are actually neglected on the street as beggars/destitute as a result worsening the disability situation. When one considers that majority of the causes are preventable and treatable yet hearing healthcare is not available to those who need it.
Expectedly, due to lack of inclusive education and poverty level, most of these students have educational delay evident by a late start in this facility; all the students were ≥10 years of age, attending primary education for the 1 st time. This may be due to lack of awareness, an inadequate number of these schools and perhaps long distance from the parents' place of domicile, as this school serves three nearby states as well.
Regarding disabling hearing impairment, a low prevalence was recorded in our study. This is comparable to the 3.8% reported in a population-based survey from Brazil.  This near equal prevalence though must be interpreted with caution as there is a large disproportion in the sample sizes. However, the point needs to be made that in our setting due to a gross lack of awareness on the impact of these impairments and treatment options; the deafblind are at constant risk of social exclusion. Similarly, it was observed that the students discovered with hearing impairment were not even aware they had a hearing loss.
The unilateral hearing loss recorded among students had no known/established causes as none could tell or recall the probable cause of this finding, despite normal findings from otoscopic examination [Figure 1]. Agreeably, what comes to mind following the discovery of impacted wax, OME or even trauma in this age group is unilateral hearing loss. Perhaps there are other confounding factors which our study may be unable to explain at this time. Although considering the poor educational and socioeconomic background of some of the parents and/or students themselves, it is reasonable to imagine that their health seeking behavior is poor. These were some of the risk factors also identified by Beria and Baraky in Brazil, , as well as in Peru and Yemen. , Majority of our subjects with unilateral impairment were males and only one female was noted, this is similar to the finding in a study in Oman. 
In another Omani study looking at dual disabilities, it was reported that females and older age groups had a higher risk of double disability than males and younger age groups.  However, the sex predilection in favor of males in our study may be due to the higher number of males in the blind school and not necessarily due to any genetic or hereditary reason. Moreover, socioculturally emphasis is given more to male than female education in our setting. Similarly, being in the meningitis belt, we may hypothesize that most of the unknown causes for dual disabilities could be due to poorly treated or undiagnosed meningitis, CRS, mumps or measles. However, in this blind school, only one child had hearing impairment in addition to total blindness for one to consider retrospectively, a diagnosis of CRS. We, therefore, hypothesize that CRS may not be as common in these cohorts as speculated. , Although majority of the students are blind with others manifesting with severe visual impairments, no other case of severe deafblindness was recorded [Table 2].
Majority of the students had normal hearing, but obstructing wax was a leading cause of ear discomfort despite good hearing [Figure 2]. This is in conformity with other studies within and outside the country with very small variations. ,, This is quite significant because it could be a precursor to other types of otitis externa,  as well as affecting the students' daily self-care or basic ADL index. This may actually be alarming when we consider higher frequencies from other larger surveys, as in the Olusanya et al. study.  In contrast, a Saudi Arabian survey to assess hearing loss among school-entrant children revealed OME (OME - 34.9%) as a leading cause followed by wax.  This may be due to the fact that they had the liberty of conducting tympanometry and also assessed bone conduction which was not possible during our survey due to financial constraints, as it was also just a screening survey. Moreover, they assessed children aged 4-8 years among whom conductive hearing loss is quite common as a cause of hearing impairment, compared to our subjects who were between 10 and 25 years of age in whom OME presents less of a problem with regard to hearing impairment except in certain circumstances such as poorly treated acute/chronic otitis media and/or masses in the postnasal space.
Looking at the median thresholds for hearing on the right and left ears (22.03 dB HL and 20.50 dB HL, respectively). Asymmetry is immediately obvious; however, this difference was not statistically significant. Anecdotally, it is believed that blind persons have an acute sense of hearing  and we would expect to find their thresholds at around 0 dB or less. In this study, we found higher threshold values. Perhaps there were other confounders which may have contributed to this, such as decreased neuroplasticity of this group or effect of ambient sound and lack of a soundproof booth (which is expensive to provide for field surveys) or from other sources of environmental noise. This was particularly so at 500 Hz for 25 dB amongst quite a sizeable number of students during this survey [Table 3]. One study, however, reported that audiometric test results conducted in nonsound proof environments in the field are comparable to those obtained in a soundproof booth with a hearing loss of >25 dB. They posited that hearing threshold at 4 KHz appears suitable for the estimation of the prevalence of hearing loss when appropriate adjustments are made in the diagnostic criteria,  although the diagnostic criteria used was different from ours.
|Table 3: Median and percentiles values of threshold scores for both ears at different frequencies|
Click here to view
The prevalence of CSOM and otomycosis was quite small which otherwise is expected to be higher when compared to other preschool and school hearing health assessment surveys.  This may mean that either the blind students have very good personal hygiene or they are well taken care of.
Agreeably, this survey has some limitations such as the frequencies at 0.5 kHz may not be reliable owing to occasional high ambient noise levels as evident by a high value at the 90 th percentile [Table 3]. As with most cross-sectional studies, recall bias is not uncommon in most subjects with hearing impairment. We used PTAv according to WHO criteria even though we are aware; it does not address those with purely unilateral and/or conductive hearing losses. We did not have the luxury of pneumatic otoscopy and/or tympanometry to confirm OME but instead we used a tuning fork.
Due to our small sample size and the bias in using only this blind school, it may be difficult to make population-based conclusions. Gilbert and Foster have reported that only about 10% of blind children are in special schools,  more so, during the survey we noted that the school had just resumed from a brief vacation, and some students had not resumed fully while others perhaps, due to prolonged waiting times got bored and/or disinterested and, therefore, refused to participate. Thus further reducing the sample size although we may argue that some of these absentees may/may not have had any preventable ear or hearing disorder.
In the future, we may need to assess the impact of hearing or visual impairment on their academic performance. It may also be worthwhile to study spatial hearing in this special population especially those with unilateral hearing impairments.
| Conclusion|| |
This special population has a low prevalence of hearing impairment. Sustained efforts are needed towards promoting safe aural hygiene practices, strengthening hearing screening and introducing sustainable rehabilitative access for hearing aids for the institutionalized blind or persons with dual disabilities. This could be in the form of regular audiological measurements among the visually challenged. This will go a long way in improving their quality of life and academic performance as well as social integration.
We solemnly thank our ever-ready companion and teacher in the special school, Abubakar T.H., who helped in the interpretation of the protocol in sign language, assessment plus logistics and Mallam Sa'adu Kauru of the National Ear Care Centre Kaduna, our audiometrician.
Financial Support and Sponsorship
Conflicts of Interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]