CHAPTER 13 Sensory Impairments: Hearing and Vision Desmond P. Kelly, MD, FAAP Introduction The ability to accurately receive and interpret a variety of environmental and internal somatic signals comprises the domain of sensory neurological functioning. In addition to the 5 major sensory systems (vision, hearing, touch, taste, and smell), other internal sensory systems provide and integrate other types of information about the body’s current status and safety. These include sensations of pain, hunger, and temperature, as well as integrated awareness of body position in, and movement through, space (kinesthesia), using vestibular and proprioceptive functions. This chapter focuses on the conditions resulting from impairments or loss of hearing and/or visual function. Although these 2 major sensory systems and their respective dysfunctions differ considerably, the following descriptions also illustrate several common features: As infants and children progress through normal neurodevelopmental stages, both visual and auditory information are integral components of other central nervous system (CNS) domains, eg, language and nonverbal concept development, motor skills, and social interactions. When these sensory signals are distorted or diminished, the child’s CNS can learn to rely more on alternative sensory information in the child’s quest for understanding, interacting with, and moving through his or her world. For primary pediatric health care professionals, similar broad diagnostic and intervention goals emerge for both vision- and hearing-impaired children and their families. These goals include the following: systematic screening/ early detection and accurate diagnosis; coordinated early intervention services and targeted special education; awareness of recent trends in technology for screening, diagnosis, and treatment; and the critical importance of advocacy for families and helping them find supports. Even mild degrees of hearing loss can impede language, social, and learning abilities. Universal newborn hearing screening has significantly lowered the average age of identification of hearing loss, but many eventually identified children, especially those with progressive or delayed onset of hearing loss or those with inadequate or inconsistent access to health care, are unfortunately still diagnosed only after crucial developmental opportunities have been missed.1,2 Comprehensive treatment with early identification, amplification of hearing, and educational interventions to promote communication facilitate optimal outcomes. Primary pediatric health care professionals must therefore be knowledgeable regarding screening and diagnosis of hearing impairment and the interventions that enable optimal functional outcomes for children with hearing loss.1,2 Epidemiology and Etiology The prevalence of hearing loss varies depending on the population studied, but the overall rate of congenital severe-to-profound bilateral sensorineural hearing loss (SNHL) has remained stable at about 1 to 2 per 1,000 live births.3 A further 2 to 3 per 1,000 subsequently acquire severe loss. Many more children suffer milder degrees of hearing impairment or unilateral hearing loss. The broad categories of hearing impairment include sensorineural (dysfunction of the cochlea and/or its neural connections to the cortex) and conductive hearing loss (interruption along the conductive pathways, eg, the pinna, external auditory canal, tympanic membrane, and middle ear structures]), or a combination of SNHL and conductive hearing loss. A genetic etiology is the most likely explanation in about 50% of cases, if other investigations have failed to identify a definite cause for a child’s hearing loss. In children with an identified genetic cause, 30% have an identified syndrome. Table 13.1 lists a few of the more common syndromes that are associated with hearing loss. Of those children with nonsyndromic hearing loss, 80% have an autosomal recessive pattern of inheritance, frequently with no family history of hearing loss or external physical manifestations of the disorder.4 X-linked and mitochondrial inheritance account for only 1% to 2% of non-syndromic hearing loss.5 More than 100 loci for genes associated with nonsyndromic hearing impairment have been identified.4,5 Mutations in the gap junction proteins beta 2 and beta 6 (GJB2 and GJB6) are a common cause of hearing impairment, and a mutation of GJB2, which encodes the connexin protein 26 (critical for potassium homeostasis in the cochlea), is responsible for up to 50% of the hearing loss in certain populations.5 Prenatally acquired causes of hearing impairment include congenital infections (eg, toxoplasmosis, rubella, cytomegalovirus, herpes simplex, and Zika virus6), and prenatal exposure to toxins such as alcohol and mercury.2,3 Extremely premature infants are at increased risk of hearing loss due to a variety of factors including hypoxia, acidosis, hypoglycemia, hyperbilirubinemia, high levels of ambient noise, and ototoxic drugs, such as aminoglycosides and diuretics. Immunization has decreased the incidence of bacterial meningitis, which is associated with SNHL in up to 10% of cases.3 Audiological follow-up of these children is essential, as the hearing loss can be progressive. Prolonged exposure to loud noise, either environmental or recreational (especially related to the use of audio headphones or ear pieces), is an increasingly common cause of high-frequency hearing loss (Table 13.2).
Stuart W. Teplin, MD, FAAP
Table 13.1. Genetic Syndromes That Are Associated With Hearing Loss | |
Syndrome | Associated Clinical Features |
Autosomal Dominant | |
Waardenburg | White forelock, heterochromia iridis, lateral displacement of inner canthus of eyes, and vestibular dysfunction |
Alport | Progressive high-frequency SNHL and specific form of glomerulonephritis |
Branchio-oto-renal | Preauricular pits and pinna abnormalities, renal anomalies (hypoplasia/ dysplasia), mixed hearing loss; can have temporal bone abnormalities |
Stickler | Cleft palate, flat facies, myopia, retinal detachment, high-frequency SNHL, spondyloepiphyseal dysplasia, and hypotonia |
Treacher Collins | Bilateral symmetrical pinna abnormalities, malar hypoplasia, down-slanting palpebral fissures, and malformation of external ear (conductive hearing loss) |
Autosomal Recessive | |
Usher | Retinitis pigmentosa and vestibular dysfunction (3 types with varying degrees of hearing loss—progressive) |
Pendred | Progressive high-frequency loss, enlarged vestibular aqueduct, incomplete partitioning of the cochlea, and thyroid dysfunction |
Jervell and Lange-Nielsen | Absent vestibular function (motor incoordination) and cardiac conduction problems (prolonged QT interval) |
Table 13.2. Degree and Effects of Hearing Lossa | ||
Degree of Hearing Loss | Hearing Level (dB) | Effects (if not corrected) |
Normal | 0-15 | • Can detect all aspects of speech |
Minimal | 16-25 | • May miss up to 10% of speech • May respond inappropriately • Peer social interaction affected |
Mild | 26-40 | • May miss up to 50% of speech • May be labeled as “behavior problem” and “poor listener” |
Moderate | 41-55 | • May miss 50% to 100% of speech • Speech quality likely to be poor • Vocabulary limited • Has compromised communication ability |
Moderate/ Severe | 56-70 | • One hundred percent of normal volume speech lost • Can have delayed speech and poor intelligibility • Social isolation is likely |
Severe | 71-90 | • Loud voices heard only within 12 inches of the ear • Has delayed speech and language if loss is prelingual • Has declining speech ability and atonal voice if loss is postlingual |
Profound | 90+ | • Sound vibrations felt rather than heard • Is unable to communicate other than through visual or tactile cues |
a Adapted with permission from Bachmann KR, Arvedson JC. Early identification and intervention for children who are hearing impaired. Pediatr Rev. 1998;19:155–165.
The key to an optimal outcome for the child with a hearing impairment is early identification and intervention. In 2007, the Joint Committee on Infant Hearing, which includes representatives from the American Academy of Pediatrics (AAP), issued an updated position statement reaffirming the recommendation for universal screening of newborns for hearing loss.2 The US Preventive Services Task Force, in its 2008 update, affirmed that there is good evidence that newborn hearing screening is highly accurate with limited evidence about harms of screening.7 It is also recommended that all infants who have risk indicators for delayed onset or progressive hearing loss should have regular assessment of hearing every 6 months until age 3 years.
The Centers for Disease Control and Prevention (CDC) Early Hearing Detection and Intervention Program has set “1–3-6” goals. These goals are hearing screening before 1 month of age, diagnostic audiological evaluation for children with hearing loss before 3 months of age, and early intervention for these children before 6 months of age.1 Despite the success of the hearing screening initiative (more than 95% of newborns are screened for hearing loss), diagnosis is often delayed. Less than 60% of newborns who fail screening have a documented diagnosis, and 77% of those diagnosed with hearing loss receive intervention services by 6 months of age. The US Department of Health and Human Services held an invitational workshop in 2008, with recommendations subsequently published, to improve the quality of tracking following newborn hearing screening and to follow up for diagnosis and early intervention.1 Recommendations included goals to (1) improve screening protocols and diagnostic testing before discharge from the NICU, (2) link infants who did not pass screening with a medical home provider, (3) increase timely access to effective early intervention services, (4) develop initiatives to improve access to loaner hearing aids, and (5) create a systematic process for monitoring developmental outcomes with the involvement of families and children. Primary pediatric health care professionals must also be alert to recognize signs of delayed or progressive hearing loss in children, especially those with risk factors as outlined in Box 13.1.
Primary pediatric health care professionals should not rely only on behavioral symptoms to identify hearing loss, although such symptoms might lead parents to raise concerns. The obvious manifestations of hearing loss include failure of an infant to startle to loud noises or to turn to localize a sound. Toddlers might not respond to environmental sounds or might appear to ignore requests or instructions or request a higher volume on electronic sound sources. Hearing loss might also manifest as social-emotional developmental delays, including behaviors that could be interpreted as features of autism spectrum disorder (ASD). A key clinical sign in children with severe to profound hearing loss is the failure to develop “canonical babbling” (use of discrete syllables such as “ba,” “da,” and “na”) by 11 months. It should be noted that youngsters with even a profound hearing loss will begin to vocalize before 6 months of age, although further language development is impeded. If there is any suspicion of hearing loss or any delays in language development or social communication, there should be no delay in referring that child for formal audiological evaluation. Likewise, in children with otitis media with persistent middle ear effusion, the level of hearing loss should be documented and monitored closely.
Box 13.1. Risk Factors and Red Flags for Delayed Onset of Hearing Loss
▶Caregiver concern regarding hearing, speech, language, or developmental delay
▶Family history of permanent childhood hearing loss
▶Neonatal intensive care of more than 5 days or any of the following regardless of length of stay:
– ECMO
– Assisted ventilation
– Exposure to ototoxic medications (gentamicin and tobramycin) or loop diuretics (furosemide)
– Hyperbilirubinemia requiring exchange transfusion
▶In utero infections (eg, cytomegalovirus, rubella, syphilis, herpes, toxoplasmosis, or Zika virus)
▶Craniofacial anomalies (involving the pinna, ear canal, ear tags, ear pits, and temporal bone anomalies)
▶Syndromes associated with progressive hearing loss such as neurofibromatosis, osteopetrosis, Usher syndrome, and other more commonly identified syndromes (see Table 13.1)
▶Neurodegenerative disorders such as Hunter syndrome
▶Sensory motor neuropathies such as Friedreich ataxia and Charcot-Marie-Tooth syndrome
▶Postnatal infections associated with SNHL including bacterial and viral (herpesvirus and varicella) meningitis
▶Head trauma, especially basal skull/temporal bone fractures
▶Chemotherapy
Abbreviation: ECMO, extracorporeal membrane oxygenation.
Adapted with permission from American Academy of Pediatrics, Joint Committee on Infant Hearing. Year 2007 position statement. Principles and guidelines for early hearing detection and intervention programs. Pediatrics. 2007;120(4):898–921.
Developmental Impact of Hearing Loss
Delayed development of speech is a universal symptom of hearing impairment, and even milder persistent degrees of hearing impairment can cause difficulties with language development, especially the processing and production of the softer, higher frequency sounds, such as some consonants (eg, “s” and “t”). Some degree of impairment of later language development and function is likely in children whose hearing loss is not corrected before 12 months of age. The degree of language delay is dependent on the severity and timing (prelingual or postlingual) of the hearing loss and the adequacy of intervention. Although expert opinions have varied over the years, it is now agreed that deafness per se does not impart limitations to cognition. However, some children who are deaf have less cognitive flexibility.
Most thought processes are mediated by language, and studies of children with deafness show that they place greater reliance than hearing children do on visual-spatial, short-term memory rather than on temporal-sequential coding.8 Some studies indicate more efficient visual processing abilities. Children with associated vestibular dysfunction are at increased risk for difficulty with balance, equilibrium, and related motor skills. Children who are deaf or hard of hearing have been described as less socially mature. Language and communication is, of course, a central component of all social exchanges. A hearing evaluation should be the first step in the evaluation of any child suspected of having ASD. Although there has been a paucity of research regarding attention deficits in children who are deaf, it is clear that a youngster who is reliant on visual input for learning and communication would be at double jeopardy for learning problems if he or she also had attention weaknesses. Studies utilizing parent and teacher questionnaire ratings at a residential school for children who are deaf found that the overall prevalence of attention deficits in children who are deaf was not higher than for the general population. However, in that study, children with acquired deafness, eg, as a consequence of bacterial meningitis, manifested an increased prevalence of both attention deficits and learning disabilities.9
The most recent Annual Survey of Hearing-Impaired Children and Youth by Gallaudet University in 2010 reported that 39% of deaf children were classified as having educationally significant associated disabilities, with many of those being related to the same factor that caused the deafness.10 Children with hearing impairment are at particularly increased risk for reading disabilities. In the Gallaudet University survey, 95% of students received some type of assistive services, with the most common being audiological follow-up and speech and language therapy, followed by 12% receiving occupational or physical therapy. Learning resource services were received by 12% and tutoring services by 8%.10
Unilateral hearing loss was previously considered to have little long-term effect on development. However, in a more recent study, children with hearing loss in one ear demonstrated lower oral language scores than their siblings with normal hearing, with an associated increased risk for subsequent learning problems.11
Assessment of Hearing
Screening of hearing in the clinical office setting using automated otoacoustic emission (OAE) measuring devices or audiometers can be a useful first step. If there is any question of hearing impairment, the child should be referred for formal audiological evaluation.12
Objective measures are most reliable in infants and younger children who cannot provide consistent behavioral responses. Auditory evoked potentials are electrophysiological responses that assess auditory function and neurological integrity. A click is introduced by an earphone or headphone at the external canal and the transmission of the low-energy evoked potential through the brainstem pathways to the auditory cortex is recorded by means of scalp electrodes. It is important to note that auditory brainstem response (ABR) testing does not measure how the sound is being interpreted and processed, and it should be used in conjunction with behavioral audiometry whenever possible. OAE testing measures the integrity and sensitivity of the cochlea as well as indirectly reflecting middle ear status. The OAE are a form of acoustic energy produced by active movements of the outer hair cells of the cochlea in response to sound. Testing entails the introduction of a click via a probe in the ear canal with measurement of the emissions from the inner ear by a microphone. This test is relatively simple and highly sensitive, but it is less specific than ABR testing and can be affected by outer ear canal obstruction and middle ear effusion. Otoacoustic emissions testing can also be inaccurate in specific circumstances, including auditory neuropathy, in which the outer cochlear hair cells are normal but the inner hair cells and/or auditory nerve are dysfunctional.
Hearing tests that elicit behavioral responses allow for more frequency-specific testing and confirmation that sound is being perceived by the child. Behavioral observation audiometry can be used in very young infants (birth—6 months) to establish estimated levels of hearing. This technique entails controlled observation of an infant’s behavioral response to sound stimulation under controlled conditions. These responses include the auro-palpebral reflex, startle and arousal responses, and rudimentary head turning. This type of testing is prone to relatively high false-negative and false-positive responses. Visual reinforcement audiometry can be used in children by 6 months of age, and it is particularly helpful in the 1- to 4-year-old age range. The child is conditioned to animated, lighted toys placed such that when the child turns in response to sound from the speaker, the toy at that speaker is lit to reinforce the response. After conditioning, the sound is presented before the toy lights up. Play audiometry can be used in children 2 years of age and older as attention spans increase. The child responds to sound by performing tasks such as dropping or stacking blocks or placing rings on pegs. Pure tone and speech audiometry provide more accurate measurement of responses to pure tones or speech where older children are asked to respond to signals generated by a calibrated audiometer. The use of speakers has the limitation of reflecting hearing only “in the better-hearing ear,” and once children accept the use of headphones, more accurate assessments can be made for each ear. The results of hearing tests are represented graphically on an audiogram, which displays the auditory threshold in decibels as a function of frequency in hertz.
Medical Evaluation
When hearing loss has been identified, further medical assessment is necessary. A thorough history can establish risk factors and potential etiologies.2 In children with SNHL, it is essential to rule out any associated conductive component. A detailed, general physical examination should include pneumatic otoscopy and tests of vestibular function. Comprehensive evaluation is important to look for associated disabilities. For example, unexplained fainting spells in a deaf child might signal a cardiac conduction defect (long QT interval) of Jervell and Lange-Nielsen syndrome. Ophthalmological evaluation is also essential to rule out conditions such as retinitis pigmentosa with progressive loss of vision, which occurs in children with Usher syndrome. Chorioretinitis accompanies some of the congenital infections, and this finding might help establish an etiological diagnosis. Routine evaluation for refractive errors is important to ensure optimal vision for these children, who are more reliant on visual input for communication and learning.
The extent of special investigations to be performed depends partly on clinical presentation. It is currently recommended that all children with SNHL should have a high-resolution computed tomography (CT) scan of the temporal bone to rule out conditions such as an enlarged vestibular aqueduct (associated with progressive hearing loss) or abnormalities of the cochlea and semicircular canals. Magnetic resonance imaging scans, especially 3-dimensional, can identify anatomical abnormalities (eg, cochlear anomalies that might preclude cochlear implantation) or neoplasms, and a CT brain scan might also reveal calcifications indicating congenital infection. Genetic testing is evolving rapidly and enabling specific diagnosis in many children previously classified as having hearing loss of undetermined etiology.5 In addition to molecular testing for GJB2, the identification of other mutations, including SLC26A4 (the second most common nonsyndromic form of SNHL, which may also cause Pendred syndrome) and A1555G (a mitochondrial gene mutation that causes deafness due to extreme sensitivity of the cochlea to aminoglycosides), could be considered. If more complex genetic testing is being considered, consultation with a geneticist is recommended both for interpretation of test results and counseling regarding associated risks. Next-generation sequencing and other advanced techniques will likely soon enable definitive diagnosis of all possible genetic causes of hearing loss.5 Other special investigations could include tests of renal function or metabolic function, immunological testing, or an electrocardiogram depending on clinical findings. If congenital or acquired infection is suspected, consultation by a pediatric infectious disease specialist is helpful in ordering and interpreting immunological tests (cytomegalovirus, toxoplasmosis, rubella, herpes, syphilis, and Zika virus).
Developmental Evaluation
Although hearing loss is not associated with cognitive impairment (unless there has been associated neurological damage in those children with acquired hearing loss), careful assessment of language and learning abilities is essential to ensure appropriate planning for developmental and educational interventions.
Formal assessment of cognitive, language, and social abilities should be carried out by professionals who have experience in testing children with hearing impairment. Tests of cognition can include the performance subtests of the Wechsler Intelligence Scales12 (WISC-V), the Leiter International Performance Scale–Revised,13 and the Differential Ability Scales, Second Edition, Nonverbal Reasoning Index.14 The latter two assessments have been shown to produce equivalent results when administered to children with hearing loss.15
Treatment
Comprehensive management should include attention to medical conditions, interventions to promote language development, educational interventions, use of assistive devices, and support and advocacy.16,17 This is best accomplished by a team of professionals working in partnership with families, the primary pediatric health care professional, otolaryngologist, audiologist, speech-language pathologist, and an educator of children who are deaf or hard of hearing.
Primary pediatric health care professionals, working with parents and other health care professionals, provide the medical home to facilitate and coordinate many of these interventions. Audiologists confirm the existence and degree of hearing loss and provide recommendations for amplification and assistive technology. Otolaryngologists will be able to assess middle ear function and evaluate for any surgically correctable causes of hearing loss, such as cholesteatoma, ossicular abnormalities, or other anomalies of the conductive system. They can also provide consultation regarding candidacy for cochlear implantation.
When a significant hearing loss has been discovered, the child should be fitted with a hearing aid as soon as possible. Hearing aids can be fitted in infants based on estimates of hearing thresholds from ABR measurements. Once a child is old enough to participate in behavioral hearing tests, these results can be incorporated into more precise calibration of hearing aids. The goal of amplification is to make speech and other environmental sounds audible while avoiding high-intensity sound levels that are aversive or could damage residual hearing. A variety of forms of amplification are available, including behind-the-ear or ear-level hearing aids that fit behind the pinna with amplified sound transmitted to the ear canal via the custom-fit ear mold. Smaller, in-ear devices are not recommended for young children because of the risk of swallowing or aspiration. Amplification devices can also be used with telephones and with direct input from FM auditory systems, where the primary speaker (usually the classroom teacher) wears a microphone that transmits the speaker’s voice directly to the hearing aid. Bone conduction devices are used for children with certain types of conductive hearing loss, such as atresia of the external auditory canal.15
While hearing aids are effective for children with moderate to severe hearing loss, cochlear implants have revolutionized the treatment of profound hearing loss.17 Components of cochlear implants include a microphone, usually worn behind the ear, that transmits sounds to a speech processor that converts the sound into an electric code. An external coil then transmits the signal across the skin to the internal receiver system implanted within the temporal bone and connected to multichannel electrodes placed within the cochlea. The electrodes are located at different sites to use the tonotopic organization of the spiral ganglion cells within the cochlea. Cochlear implants provide significant improvement in appreciation of sound in everyday situations, speech recognition and understanding, and expressive language abilities. Recent studies have demonstrated lack of significant surgical complications and positive functional outcomes, even in children who receive their implants before 12 months of age.18 Implantation before 2 years of age (preferably before 12 months of age) has been found to provide the greatest advantage with regard to speech perception and language development, with studies suggesting that most children with profound deafness who receive implants will enter school with near-normal language skills. Children who use any form of amplification device, and especially those who have cochlear implants, need comprehensive and coordinated follow-up with specialized speech and language therapy and auditory training to help them understand the meaning of the newly amplified sounds and to develop optimal language abilities.
A variety of assistive devices are available, including telecommunication devices for the deaf, closed captioning of television, and adapted warning devices such as vibrating devices or flickering lights that indicate a ringing alarm or telephone. Advances in information technology have, of course, enabled enormously increased opportunities for communication for individuals with hearing impairment. The Internet and e-mail, as well as smartphone text messaging and voice-to-text technology, have broken down barriers at many levels.
Early intervention to promote language development remains the most critical management challenge for children with hearing impairment.19 The child with profound hearing loss and his or her parents and other caregivers should receive professional assistance to establish a functional system of communication as soon as possible. There are many differing opinions regarding the most appropriate communication and instructional techniques. Options include sign language (manual communication), lip reading and use of speech (oral communication), or a combination (total communication). Children with profound hearing loss who have not received cochlear implants usually experience great difficulty learning to read lips and speaking fluently; they are best served by early exposure to visual and manual forms of communication such as sign language. However, children with milder degrees of loss, and those who have received cochlear implants, are better able to communicate with those who have normal hearing by developing their oral language skills. Children will be best served by early intervention providers who have specialized knowledge and skills related to working with children who are deaf or hard of hearing and who have the professional qualifications to optimize the child’s development and the child’s and family’s well-being.
The advent of universal, newborn hearing screening has provided a unique opportunity to study the effects of early intervention on child development, particularly as related to hearing impairment. Studies involving children in the Colorado Home Intervention Program20 definitively established that early intervention services for families with infants with hearing loss identified in the first few months of life resulted in significantly better language, speech, and social-emotional development. Children who were diagnosed and received services before 6 months of age did significantly better than those diagnosed later, in whom intervention kept language delays from increasing but did not enable them to catch up with regard to delays that were already present at the time of diagnosis.20
For school-aged children, educational interventions should be tailored to the individual needs of each student. These services are mandated through the Individuals with Disabilities Education Act (IDEA). Options for those whose hearing loss has not been fully corrected range from use of interpreters in a regular school and classroom to special programs in a regular school or enrollment in a school for the deaf. Students with hearing impairment have the right to receive the range of amplification and technological interventions in the school setting, which were described earlier, as well as testing accommodations and regular reevaluations (usually every 3 years) to determine whether any additional learning difficulties have emerged. They must have the opportunity for full participation in both academic and social activities. The optimal school setting to achieve this goal depends on individual characteristics of the child and the educational system in that geographic region.
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