Types And Degrees of Hearing Loss
Types of Hearing Loss
There are three types of hearing loss: conductive hearing loss, sensorineural hearing loss, and mixed hearing loss.
Conductive Hearing Loss
Conductive hearing loss results in a loss of loudness; sounds are just not loud enough to be well heard. Conductive hearing loss results from an abnormality of the outer or middle ear. This type of hearing loss can be permanent or temporary depending on the cause of the hearing loss. If there is fluid in the middle ear, the loss is temporary if given prompt medical attention. Other causes can be remedied by medical or surgical techniques or by amplifying sound with hearing aids. Some causes of conductive hearing loss are otitis media, wax impaction, perforated eardrum, and cholesteatoma.
Sensorineural Heairng Loss
A sensorineural hearing loss means there is a problem in the inner ear. Sensorineural hearing loss in young children can be caused by certain infections before birth, from genetic factors, or from a lack of oxygen during birth. There is typically no medical or surgical treatment to correct for sensorineural hearing loss, but hearing aids can help in most cases.
Sensorineural hearing loss can cause not only a loss of loudness, but also clarity of speech. Sometimes, sensorineural hearing loss is incorrectly referred to as “nerve deafness”. It is not completely possible to correct the lack of clarity that may be associated with a sensorineural hearing loss by amplifying sounds. It is important to be aware of the difference between a conductive and sensorineural loss. This is the reason why some people with hearing loss seem to benefit more from hearing aids than others. When it is determined that hearing aids provide little to no clarity for someone with sensorineural hearing loss, a cochlear implant can be considered.
Mixed Hearing Loss
Mixed hearing loss is a combination of conductive hearing loss and sensorineural hearing loss. Chronic ear infection can result in a defective eardrum or middle ear cavity, and often in addition to the conductive hearing loss, the individual may have a sensorineural hearing impairment. The optimal treatment for this type of hearing loss requires consideration of all of the factors involved and must be individualized for the patient. The option of hearing aids versus reconstruction of the middle ear hearing mechanism is considered on a case-by-case basis.
Degrees of Hearing Loss
Hearing loss is measured in decibels (dB) hearing level (HL). The hearing level represents the softest level heard and is used to determine the degree of hearing loss. Degree of hearing loss is classified as mild, moderate, moderately severe, severe, or profound. Hearing loss is more accurately defined by degree rather than a percentage. Hearing levels are not always the same in each ear or for all the frequencies tested. For example, some children have a high frequency hearing loss, which is when hearing is normal in the low to mid frequencies with hearing loss in the higher frequencies, resulting in the child “hearing” some sounds, but not hearing all the sounds needed for speech understanding. The degree of hearing loss is an important factor when choosing a hearing aid. Not all hearing aids will suit all degrees of hearing loss.
Children with normal hearing can usually hear sounds quieter than 15 dB. When hearing levels are outside the normal range, they are considered to have one of the following degrees of hearing loss:
Mild Hearing Loss (16 to 40 Db Hl)
Children with a mild degree of hearing loss will have difficulty hearing sounds softer than 16 to 40 dB HL. With mild hearing loss, children cannot hear soft speech, whispering and distant speech. Understanding conversation in a noisy environment will also be challenging. A mild hearing loss is similar to blocking the ear with a finger; people can still be heard talking, but it sounds muffled and it’s even more difficult to understand the conversation if there is any background noise.
With hearing levels of 20 dB HL, the child may miss up to 10% of the speech signal when the speaker is at a distance greater than 3 feet. The percentage of speech missed will be greater whenever there is background noise. With hearing levels of 30 dB, the child may miss 25 to 40% of the speech signal. With hearing levels of 40 dB, the child may miss 50% of classroom discussions.
Hearing is not an all or nothing phenomenon. Even a mild hearing loss during the crucial years for language and speech development can cause a child to misunderstand speech sounds and may result in a delay of normal communication development, and difficulties learning early reading skills such as letter/sound associations. For mild hearing loss, hearing aids are beneficial, but are not always mandatory. Sometimes a frequency modulation (FM) system can be used in a classroom setting rather than a hearing aid to provide access to speech sounds. However, it is important that the parents, pediatric audiologist, and physician consider the child’s configuration of hearing loss, age, speech and language development, school performance, behavioral concerns, and other factors prior to deciding whether or not to proceed with amplification; in cases where it is decided that the child not yet be fitted with hearing aids, it is especially important that the child’s hearing loss and abilities be monitored so that amplification can be provided as soon as concerns develop. When these children receive hearing aids or an FM system, they usually find that school is easier as they do not have to exert as much energy to listen.
Moderate Hearing Loss (41 to 55 Db Hl)
Children with a moderate degree of hearing loss have problems hearing sounds softer than 41 to 55 dB HL. With a moderate hearing loss, children will have trouble hearing conversation at a normal level, especially in noisy situations. The TV and radio may have to be turned up in order to be heard. With hearing levels of 50 dB, the child may miss up to 80% of conversations.
Hearing aids are needed to understand speech. Even with hearing aids, if background noise is present, the child may miss some of the speech signal. Without early amplification, the child is likely to have delayed or disordered syntax, limited vocabulary, imperfect speech production, and flat voice quality.
Moderately Severe Hearing Loss (56 to 70 Db Hl)
Children with a moderately severe degree of hearing loss will not hear sounds softer than 56 to 70 dB HL. Speech sounds will not be heard. Sounds that are loud to a normal hearing person will be a whisper to the child. Children with this amount of hearing loss can hear and understand only a loud voice very close to them. They usually do not develop speech and language on their own, and if they do, their speech will be poor. Consistent use of hearing aids will help these children hear conversation and learn to speak clearly.
Severe Hearing Loss (71 to 89 Db Hl)
Children with a severe degree of hearing loss have problems hearing sounds softer than 71 to 89 dB HL. Speech sounds will not be distinguishable, no matter how close the child is to the speaker. The child may respond to a loud sound such as a door slam or siren, but other loud sounds such as a phone ringing or a dog barking may not be heard.
With the help of hearing aids or cochlear implants and therapy, a child with this degree of hearing loss often can understand some speech sounds; however, with hearing aids, only a portion of the clues available in speech sounds will be provided. Children with severe hearing loss can learn to understand and speak, even though they will not hear speech the way children with normal hearing do.
If hearing loss is not identified and appropriately managed during infancy, it is likely that spoken language will be delayed; the earlier the child begins consistent use of amplification with rigorous language intervention, the greater the child’s chances are that speech, language and learning will develop at a fairly normal rate. Individual ability and intensive intervention prior to 6 months of age will determine the extent that sounds detected will be understood by the brain and processed as meaningful input.
Profound Hearing Loss (> 90 Db Hl)
Children with a profound degree of hearing loss cannot hear sounds softer than 91 dB HL. With profound hearing loss, children will receive very little auditory information; speech sounds will not be audible and even some very loud environmental sounds will not be heard. Even with hearing aids, the child may not be able to understand all speech sounds. However, a cochlear implant and therapy can help the child learn speech and language. Most children with a profound hearing loss will need help at home and school to improve their speech and language. Some children may still need to use visual cues to help them understand spoken conversation.