The topic of unilateral hearing loss (UHL) is not new to the profession of audiology, but the advent of newborn hearing screening and recent research have renewed interest in this population of children and provides audiologists and other providers the opportunity to reevaluate their practices.
Definitions of UHL have varied over the years, but generally a unilateral hearing loss is defined as a permanent loss of any degree (mild to profound) in one ear. Previously, most children with UHL were not identified until they were school-age (Brookhouser, Worthington, & Kelly, 1991). Early hearing detection and intervention (EHDI) programs are now identifying most children with UHL of a moderate degree or greater in the first weeks of life.
The Joint Committee on Infant Hearing (JCIH) Year 2007 Position Statement has clear guidelines on the early identification of infants with hearing loss, including those with UHL. This early identification of infants with UHL leaves audiologists with the need to establish best practice guidelines for this population. However, questions remain: Will this previously nonexistent "window of opportunity" brought about by early identification allow providers to be proactive in early management? Will the implementation of early management guidelines help these children avoid difficulties when they are older?
Recent data show that approximately one out of every 1,000 newborns has UHL (Prieve et al., 2000) and that by the time children reach school age, approximately 3% have UHL (Bess, Dodd-Murphy, & Parker, 1998)—a striking increase in prevalence of hearing loss between birth and school age. Although some children in the older age group had late-onset hearing loss, it is speculated that others may have had existing mild hearing loss that was not identified through EHDI. Other causes for the increased incidence may include hearing loss that was fluctuating and/or progressive.
Much of the early work describing the difficulties experienced by children with UHL was completed in the 1980s. These children were found to be at higher risk for academic, speech-language, and social-emotional difficulties than their normal-hearing peers.
Children with UHL were approximately 10 times more likely to fail a grade than their normal-hearing peers (Bess & Tharpe, 1984; Oyler, Oyler, & Matkin, 1988). Children with UHL have been found to score lower on intelligence tests; scores appear to be correlated to the degree of loss. Children with severe-to-profound UHL have been found to have a lower full-scale IQ score on the Wechsler Intelligence Scale for Children-Revised (WISC-R) than children with lesser degrees of UHL (Culbertson & Gilbert, 1986; Klee & Davis-Dansky, 1986).
English and Church (1999) reported that grade failure was no longer a "widely recommended educational practice," eliminating this basis of comparison to previous studies. However, these researchers found that more than half of children with UHL received special services in school, a finding recently replicated by McKay, Knightly, Marsh, Amann, and Gravel (2007).
Studies show that even before they enter school, children with UHL are at risk for speech and language delays. Although the average age for first words was found to be within normal limits (12.7 months), the average age for the first two-word utterances was found to be significantly delayed (23.5 months) in children with UHL (Kiese-Himmel, 2002). The Colorado Home Intervention Program collected information on children less than 3 years old enrolled in its early intervention program. Approximately 17% of the children with UHL demonstrated some degree of expressive and/or receptive language delays and 33% were judged to have a mean length of utterance below age expectations.
Children with UHL are also at greater risk for social-emotional difficulties than peers with normal hearing. Speech is audible for children with UHL, but it may not always be understandable, depending upon the listening environment. Bess and Tharpe (1986) reported that 20% of children with UHL were judged by their teachers to have behavioral problems. Bovo et al. (1988) reported that 27% of children with UHL had feelings of embarrassment and inferiority. Bess et al. (1998) found that children with UHL showed greater difficulty in the areas of behavior, energy, stress, social support, and self-esteem.
Others may misinterpret these difficulties, and perceive the child as inattentive, disinterested, or aloof. If a child must make a constant effort to listen and is not able to understand what is being said, the child may feel insecure or left out of the conversation. These feelings may cause a child to become withdrawn and can lead to difficulties with behavior and peer relations.
Teacher perceptions of children with UHL also have been studied. Because children with UHL may miss only parts of speech, their difficulties may not be obvious to others. If a teacher is not informed that a child has UHL, the teacher may never know, but may notice social and behavioral problems. Hearing aids, which typically alert teachers to children with bilateral hearing loss, are not always recommended or chosen for children with UHL due to a variety of factors (age, degree of hearing loss, or parent/child motivation). Oyler et al. (1987) found that most teachers rated the children with UHL in their classes as "underachievers." Dancer, Burl, and Waters (1995) found that teachers gave lower scores to children with UHL in all five areas on the Screening Instrument for Targeting Educational Risk (SIFTER): academics, attention, communication, participation, and behavior.
Bourland-Hicks and Tharpe's (2002) examination of the "listening effort" may help explain why children with UHL experience difficulties in school. Using a dual-task paradigm, they examined listening effort in children with and without hearing loss. Although there were no significant differences between the two groups on the primary task (speech recognition in noise) and the secondary task in isolation (pushing a button in response to a light), the children with hearing loss scored significantly lower on the secondary task when they were asked to perform both simultaneously. The authors concluded that this decrease in performance on the secondary task revealed that the children with hearing loss had to expend more listening effort to complete the primary task. Although the children in this study had bilateral hearing loss (mild- to moderate-degree or high-frequency loss), the implications may be applied to children with UHL. Throughout the school day, children are asked to "multi-task" as they listen to the teacher present a lesson and simultaneously take notes. If a child is not able to complete the secondary task (taking notes) adequately and becomes fatigued, the child's achievement may suffer.
To address these reported difficulties, intervention options for children with UHL include amplification, audiologic monitoring, functional auditory measures, and parental education.
Although amplification may be indicated for some children with UHL, the decision to fit a child should be made individually, taking into consideration the preference of the child or family as well as audiologic, developmental, communication, and educational factors. The JCIH (2007) guidelines state, "Infants and young children with unilateral hearing loss should also be assessed for appropriateness of hearing-aid fitting. Depending on the degree of residual hearing in unilateral loss, a hearing aid may or may not be indicated."
Limited information has been obtained on the efficacy of amplification for children with UHL. The use of a hearing aid for children with hearing losses up to the moderately severe range has met with some success, as indicated by subjective rating scales. Kiese-Himmel (2002) studied children with UHL who wore hearing aids and found that 81% accepted their hearing aids, based on parental judgment. There was limited or no hearing aid use with severe or profound losses. It may be possible to achieve a more balanced sense of hearing between the ears with a lesser degree of hearing loss, but not when the loss is severe or profound.
Davis, Reeve, Hind, and Bamford (2001) studied children with mild bilateral and unilateral hearing loss and their acceptance of hearing aids. Of 27 children with UHL who were fit with amplification, 26% reported wearing it all of the time, 4% reported wearing it only in school, and 50% reported never wearing it. Children with UHL wore their aids less often than those who had mild hearing loss. Interestingly, parents reported that their children had greater ease of listening in quiet and in noise when they wore their hearing aids.
A retrospective questionnaire was administered to parents of 20 children (mostly school-age) with UHL to rate the parents' perception of their child's function with and prior to amplification (McKay, 2002). The results were positive, with 72% of parents reporting benefit (improved or greatly improved) in response to questions related to their child's hearing ability in different listening environments. Parents reported little or no change in confidence or general disposition after their child was fit with a hearing aid. All of the parents were happy with their decision to have their child fit with a hearing aid, and half reported that they wished they had done so sooner.
In a study of perceived listening difficulties of children (ages 7-12 years) with UHL (McKay et al. 2007), families were asked to answer questions about hearing aid use and support services received and to complete the Children's Home Inventory for Listening Difficulties (CHILD) (Anderson & Smaldino, 2000). In this study, 46% of children who were considered candidates for amplification (excluding children with severe or profound hearing loss or external atresia of the ear) were reported to use a hearing aid. Parents reported that all children wore their aids at school and 59% wore their aids in situations outside of school. There was an association between children who wore hearing aids and those who received support services. In addition, children who wore hearing aids were found to score significantly lower on the CHILD. It is not known if the children who wore hearing aids experienced difficulties, thus necessitating amplification and intervention, or if these children's parents were more proactive in their care. It is also not known if these children experience similar difficulties in school. More research is warranted in this area.
Unlike conventional amplification, the benefit of FM technology for children with UHL has been well-documented (Flexer, 1995; Kenworthy, Klee, & Tharpe, 1990; Updike, 1994). Because children with UHL experience greater difficulty in background noise, increasing the signal-to-noise ratio is clearly an advantage. One factor that must be considered is the routing of an FM system, which may not be as straightforward as it is with children with binaural hearing aids. Although an ear-level receiver will provide an optimal signal-to-noise ratio over soundfield options (Anderson & Goldstein, 2004), different situations may warrant different deliveries.
If a child already has a hearing aid, the FM receiver may be coupled to the hearing aid. Another option is to place the FM receiver on the normal-hearing ear through an ear-level FM system, a particularly useful option if the impaired ear has a severe or profound loss. When fitting an ear-level FM to an ear with normal hearing, an open fitting should be used. Personal and soundfield FM systems may also be options, as in the case with an older child who uses an in-the-ear hearing aid. Every child has different needs, and decisions must be made on an individual basis. Selection of an FM system should be coordinated with the child's educational audiologist or teacher of the hearing impaired who may have pertinent information about the class setting, acoustics, and use of FM with other students.
Another amplification option is the use of contralateral routing of signal (CROS). Kenworthy et al. (1990) found the CROS system to be useful in quiet situations, especially when the signal originates on the side of the impaired ear. However, CROS amplification may be detrimental in the classroom because noise is introduced to the normal-hearing ear through the microphone on the impaired side. For this reason, the CROS should not be considered for young children who may not be able to monitor the effectiveness of the system.
Two fitting options now available for children with severe to profound sensorineural hearing loss (or unaidable hearing) are the bone-anchored hearing aid (BAHA) and a "transcranial CROS." Both of these devices provide transcranial delivery of sound from the impaired side through bone conduction of the skull to the cochlea of the normal-hearing ear. Because of issues related to anatomical maturation, the BAHA has been approved by the U.S. Food and Drug Administration for children older than 5 years of age. Several studies of BAHA and transcranial CROS fittings on adults with UHL have been conducted with results ranging from improvement to no improvement in the areas of speech recognition and localization. There are no studies to date, however, on the use of these devices on children with severe or profound sensorineural hearing loss in one ear. Although these devices seem to be a viable option for adults, more evidence is needed regarding the efficacy of the BAHA and the transcranial CROS for children with UHL.
Close audiologic monitoring is mandatory for children with UHL to detect any change in hearing sensitivity in either ear as soon as possible. This detection is particularly important in light of the reported risk of progressive hearing loss in this population. Children with bilateral and unilateral hearing loss should be referred for evaluations by otolaryngology, genetics, and ophthalmology (JCIH, 2007). Results of computed tomography (CT) or magnetic resonance imaging (MRI) ordered by a child's otolaryngologist may reveal whether a child has inner ear anomalies associated with progressive hearing loss. Parents and primary care providers should be made aware of the cumulative effects of a conductive overlay in children with an existing sensorineural hearing loss so that they can remain vigilant about otitis media. Referral to early intervention upon identification of UHL is recommended (JCIH, 2007). Periodic speech and language monitoring of young children may help to identify any subtle difficulties and allow for remediation before a child begins school.
Functional Auditory Measures
Functional auditory measures may be particularly helpful in tracking the ongoing auditory abilities of a child with UHL. Because audiologists do not yet have methods available to determine which children will be at the highest risk for academic difficulties, functional listening questionnaires may provide information that could help parents and professionals better understand the child's specific problems. These measures may also facilitate communication between parent, child, and audiologist. Tharpe and Flynn (2005) recommend specific functional auditory measures based on the child's age and degree of hearing loss.
When a child is identified with UHL it is important to provide parents with written information to which they can refer. Information should include the types of difficulties a child with UHL may experience; expected speech-language and auditory milestones; strategies to help their child at home; the impact of otitis media on a child with sensorineural hearing loss; and safety issues such as difficulty with localization and hearing conservation. It is also important to educate a child's teacher—including daycare or preschool teachers—about the child's potential difficulties and helpful classroom strategies. Parents should avoid placing their child in open classrooms where the poor acoustics and reverberation will affect a child's ability to understand the instruction.
Over the past 20 years, research has provided a better understanding of many aspects of pediatric UHL, including the prevalence, etiologies, and need for monitoring, intervention, and amplification. Yet many questions remain unanswered, including the most important: How can we identify which children are most likely to have difficulties? By continuing to focus attention and research on this population, including the possibility of following children from an early age after identification through EHDI, an even better understanding may be in the not-so-distant future.