Five thousand children are born profoundly deaf each year in the United States alone. Another 10 to 15 percent of newborns have a partial hearing loss or other hearing problems.
A sensorineural hearing loss is used to describe hearing impairments which result from a disruption of the conversion of mechanical viabrations in the inner ear to nerve signals, which go up to the brain. These impairments may be congenital (i.e. present at birth), hereditary, developmental, or a combination of these. In addition, these impairments may result from infections, injuries, ototoxic drug therapy, or lack of oxygen.
Hearing loss may be divided further due to the cause of the hearing handicap.
A. Congenital hearing loss
1. Genetic – In the genetic type there is an actual defect in your child’s genes which results in an abnormal development of the ear.
2. Non-genetic – This is a hearing loss which is due to some problem which occurred during the fetal development or the immediate birth period.
B. Acquired hearing loss – This is a hearing impairment which occurs sometime after birth and is not transmitted to future children.
Several viral infections, including CMV and German measles contracted by the mother during the first three months of pregnancy, may interfere with inner ear development in the fetus. Occasionally, the origin is other viruses, such as the viruses of measles and mumps. Fortunately, due to better immunization prevalence, these diseases are not as common as they once were.
Problems at Birth
A very difficult and complicated labor or premature birth may also result in an inner ear hearing impairment on occasion. This may be due to lack of oxygen. These are many syndromes which can also result in a hearing impairment at birth. One can have a hearing loss at birth without any hereditary relationship.
Jaundice occurring at or shortly after birth is capable of damaging the inner ear. This is most often due to Rh incompatibility between the mother’s and the child’s blood. Fortunately, this is not a common occurrence.
The development and function of the ear is dependent upon hundreds or even thousands of genes, interacting with each other and with the inter-and extrauterine environment. A major cause of late-onset hearing loss for children is genetic in origin. Most cases of hereditary-based childhood deafness are sensorineural rather than conductive in nature. frequencies.
Hereditary sensorineural hearing loss may be present at birth, or may develop later in life. This may be due to inner ear malformations or to other associated syndromes which have an associated inner ear hearing loss. One may see a genetic sensorineural hearing loss with or without associated abnormalities.
The most common type of acquired sensorineural loss is meningitis. Frequently this may affect both ears, but can involve one ear. Other types of infections would include viral diseases, such as mumps, rubella and otitis media.
Hearing Impairment in One Ear
A hearing impairment that is confined to one ear deprives a person of the ability to distinguish the direction of sound. He will also have difficulty hearing from the involved side in a noisy background. These are minor problems to a young child. When this hearing impairment in one ear is conductive, surgery will usually be able to restore the hearing, giving a better balance to the hearing hearing. When the unilateral impairment is sensorineural, either amplification in the poorer ear, or use of a CROS hearing aid is indicated. A CROS hearing aid (Contralateral Routing of Signal) is utilized when the hearing in the poorer ear is too poor to be aided directly. With a CROS aid, a microphone is placed on the poor hearing side and a signal is transmitted to the better hearing side.
There is no known medical or surgical treatment that will totally restore normal hearing in patients with sesorineural hearing impairments. We therefore, rely on rehabilitation through the use of a hearing aid, a cochlear implant and/or special training. Fortunately, many children with this type of hearing impairment will not show progression of the impairment as they get older.
The Hard-of-Hearing Child
If your child’s hearing impairment is in the range of 35-70 dB HL, he or she should do well with a properly fitted hearing aid. He or she will probably be able to attend school with normal hearing children. He or she will need preschool speech therapy and auditory training in order that communication abilities will be at the optimal level when regular school starts.
Hearing Aid Evaluation
The techniques involved in assessing the hearing of young children have improved over recent years. Electrophysiologic techniques such as A.B.R. and O.A.E. Testing have improved the accuracy of test results at progressively earlier ages. It is important to determine an accurate measurement of both the type and the degree of hearing impairment in order to select the proper hearing aid. Care must be taken to prescribe the correct amount of sound amplification or gain for the aided infant/toddler/child. Too much powerful and the child might reject the aid. If the aid is not strong enough, a child may receive little or no benefit from it and therefore object to wearing it. Fortunately, there are also objective measures through real-ear probe-tube microphone measurements which can both accurately prescribe as well as validate/measure the actual amount of amplification being delivered to the child.
Speech Reading – Lip Reading
Speech reading is very important whatever the type of degree of impairment. This skill enables a person with impaired hearing to understand conversation by attentively observing the speaker. All of us, whether we have a hearing loss or not, employ the sense of sight as well as the sense of hearing in ordinary conversation. We find it easier to comprehend if we can watch the speaker’s facial expressions, lip movements and gestures. .It is important to tell other family members and friends to get the child’s attention before speaking. The child with a hearing impairment must recognize characteristics of the English language. Many sounds and many words look the same on the lips. The hearing impaired child will find it impossible to see certain words on the lips and therefore needs to continuously fill in the “gaps” of words and sentences. The child, who is learning to speech read, learning to use a hearing aid, or both, should have help from a professional person trained to teach these skills.
Profound Sensorineural Hearing Impairment
With the increasing implementation of Cochlear Implants, even children with profound hearing losses will likely be able to hear sound to some degree. However, the sound will not have the same tonal quality as it does for a normally hearing person. They still may need what is called a manual form of communication and intensive auditory trainging. American Sign Language is still used, though it is not as common for younger profoundly impaired children as it is for older adults. Whether the child communicates orally, with A.S.L., or in a “total communication” invironment, they will most likely need intesive interventional help to mainstream to regular society.
There are two very important factors to be determined upon examining the child with a suspected hearing impairment. First, determination should be made regarding the presence of a hearing loss and the type (i.e., conductive or sensorineural). Secondly, once a hearing loss is found to be present, it should be determined if this loss is progressive or stable. Therefore, your child may require periodic audiograms to be sure that the hearing loss is going to remain stable.
Complete Audiologic and Otologic examinations are recommended to determine what type of hearing impairment is present, its probable cause, and its treatment. The Otologist (ENT) may recommend special x-rays of the inner ear (CT,MRI, etc), a balance test or other laboratory tests to make this decision.
A well-rounded program of rehabilitation for children with hearing loss may include speech reading, auditory training, speech therapy and instruction in the use of a hearing aid. One may also consider other adjuvants to assist with their communication skills such as cued speech or other manual techniques. All aspects of the program do not necessarily apply to each child with an impairment, but each individual may be helped through some of these methods. One cannot stress the importance of early indentification of hearing loss and early intervention. Critical speech and language development starts within the first three to four months of life.
The Cochlear Implant
The cochlear implant is an electronic device that is implanted into the inner ear of a severe to profoundly hearing impaired child. This device is only utilized in the child who can benefit more from an implant than from a hearing aid. It is a device which is used to bypass the diseased or nonfunctional hair cells and converts sounds to electrical impulses which directly stimulate the cochlear nerve. The implant consists of an external portion comprised of a microphone, sound processor, and external coil and an internal portion that must be surgically implanted. The surgical procedure involves the placement of an internal coil beneath the skin behind the ear and a stimulating electrode which is inserted into the cochlea or inner ear.
To determine suitability for this device in the severe to profoundly hearing impaired child, a careful examination is required. The evaluation is performed to determine whether or not the child can receive adequate information from a powerful hearing aid, or whether or not the implantation procedure can be performed and give the expected improvement.
Currently there are several multiple stimulating channel devices used. This is related to the number of stimulating electrodes within the cochlea.