In order to understand what damage or hearing loss is, first we need to know what is sound, what is the ear made of and understand the hearing as a process.

What is sound?

The sound that the human ear registers is called tone. The tone is characterized with a certain height and strength. The pitch ( height ) gives the frequency or number of vibrations per second and is expressed in hertz (Hz). The bigger the vibrations are, the tone is higher and vice versa. The strength or intensity of the sound is measured in decibels(dB). These two features can be represented in a coordinate system in which the vertical axis shows the intensity of the sounds expressed in decibels, and the horizontal axis shown individual frequencies (from 125 to 8000 Hz) .This graph is called an audiogram and a state of hearing.

Listening is a complex process of collecting sounds and giving meaning to these sounds. The process of listening goes through so-called auditory pathway.

Auditory path comprises:

1. External ear – consists of ear lobe and external ear canal. Your outer shell shape collects sound vibrations around you and brings it to the ear canal. It also helps in determining the direction and the sound source.
The external ear canal has a protective role i.e. the ear canal contains hairs and secretes earwax (cerumen) that prevents the entry of foreign bodies (insects, dust) in the ear. Its second role is in the implementation of sound to the ear membrane (membrane tympani).

2. Middle ear begins with the eardrum, continues with bone chain (osicular chain) composed of 3 small bones. This chain connects the eardrum to the inner ear. When sound waves hit the eardrum, it starts to vibrate and with its movement drives the auditory ossicles. Thus sound energy is converted into mechanical energy.

3. Internal ear consists of the cochlea which is a snail-shaped and is filled with liquid. Inside the cochlea is a sensory receptor i.e. Organ of Korti which contains hair cells, nerve receptors for hearing.
The mechanical energy created by the little bones in the middle ear, move the fluid keep in the cochlea that stimulates the small nerve hairs. Certain hairs respond to certain sound frequencies, so depending on the value (frequency) of the sound only certain hair cells are stimulated. The signals from these hair cells turn into nerve impulses. These impulses pass through the cochlear part of the acoustic nerve and are then transmitted to the brain.

4. The acoustic nerve carries impulses from the cochlea to the midbrain then through other brain pathways ending in the auditory part of the brain cortex.

All parts comprising the auditory pathway have to function correctly for normal hearing. This pathway includes all previously described parts: external ear, middle ear, inner ear, and the acoustic nerve, connections between the acoustic nerve and the brain. If some of these parts are damaged, there is a hearing loss.
Hearing loss means reduction in the intensity of the sounds of different frequency bands. From the point of damage to the auditory pathway depends on the type and degree of hearing loss.
We distinguish three types of hearing loss: conductive, sensorineural and mixed type.

1. Conductive type of hearing loss occurs when sounds delivery through parts of the outer and middle ear is prevented.
2. Sensorineural type of hearing loss is caused by damage to the inner ear (cochlea) or the nerve pathways that conduct sound from the inner ear to the brain (Retrocochlear).
3. Mixed type of hearing loss occurs due to damage to the outer or middle ear (conductive) and inner ear or acoustic nerve (sensorineural).

There is yet another type of hearing problem called auditory neuropathy where the cochlea, the middle and outer ear function normally but there is a problem with processing the sounds in the brain.

Hearing loss can be divided according to the degree of hearing loss as:

1. easy
2. sparingly
3. difficult
4. Very severe hearing impairment
5. total deafness

Hearing impairment may be due to the action of various factors and occur during:

• prenatal period
• perinatal period
• postnatal period

Prenatal period - following reasons or conditions are associated with the onset of hearing loss:

• Genetic causes like hereditary syndromes (Usher, Alport, Waardenburg syndrome) and genetic non-syndromic hearing impairment.
• Infectious causes: rubella, cytomegalovirus, toxoplasmosis and syphilis
• Toxins (lead, alcohol, excessive smoking, etc.).
• Drugs (chemotherapy drugs, antibiotics, antiepileptics)
• Mechanical pressure of the fetus (abnormal position of the fetus, twins, instrumentation)

Perinatal period - the most common causes in this period:

• Fetal asphyxia
• intracranial bleeding
• hyperbilirubinemy
• prematurity
• Low birth weight (less than 1500 grams).

Postnatal period - possible causes in this period:

• Infections localization of brain structures (such as bacterial meningitis)
• Middle ear infections
• Measles
• Ototoxic drugs such as antibiotics like Gentamycin, Streptomycin
• injuries
• Exposure to very loud sounds (e.g. prolonged exposure to noise over 85 decibels, 15 minutes exposure to sounds of 100 dB and a minute sound exposure of 110 dB causes permanent sensorineural hearing loss).

It should be noted that all the above shown etiologic factors not always cause hearing damage. However, due to increased association of hearing loss with the above mentioned factors they are identified as high risk factors.

Some agents that cause hearing impairment can be prevented:

• Immunization. Vaccination against H. Influenzae (one of the causes of bacterial meningitis) vaccination against measles.
• Infants with severe bilirubinemy are at risk of developing brain impairment (bilirubin encephalopathy) condition known as kernicterus. Kernicterus is preventable using special lights (phototherapy) and ex-Sangweni transfusion (blood substitute).
• Prompt treatment of ear infections
• Using protective earplugs or earmuffs when exposed to very loud sounds

Very severe hearing impairment,
total deafness

Ability to express thoughts, emotions and abstract ideas through spoken words is speech. Language is a system of symbols through which people communicate.

During the first year of life people learn about their environment through the experience. Although it is invisible, children with normal hearing in this period learn speech and language. It is called critical period. At that time the brain matures, millions of neural connections are created, which in absence of sound stimulation are interrupted, thus the morphology and function of neurons in the central auditory system is disturbed. But this detrimental effect of lack of sound stimulus can be reduced or avoided by the introduction of sound stimulation, for example by using hearing aids. With timely application of the instrument permitting better social communication, and also slows down the progression of hearing loss.

The representation of the reduction of hearing in newborns is relatively high. Namely, it is estimated that one in 300 newborns suffering from moderate to severe hearing loss. However, of particular importance are the consequences of reduced hearing, and they are developmental disorders of speech and language, and disruption of socio-emotional and cognitive development. Studies show that children with mild to moderate hearing loss may miss 50% of the conversations and the age of six years to hold 50 to 60 words. Child with average hearing at the same age owns about 3000 words. Without proper speaking abilities, children with severe hearing can also be misdiagnosed as mentally retarded, autistic, etc.
Failure to perform specific testing, hearing loss in newborns can remain undetected until the end of the second year of life, with a large number of children who are not identified until the 5th or 6th year of life. In their procedure for encouraging the development of speech, language and learning will be delayed, and the consequences remain for a lifetime. But when hearing loss is detected in infancy or early after the occurrence of hearing loss (later acquired in damages), children can have a benefit of amplification (hearing aids) and early intervention that will facilitate overall development.

Early identification of hearing loss and rapid intervention and rehabilitation are two key elements that will give the child the greatest chance for normal development of speech which in turn will affect the socio-emotional development, and the cognitive abilities as well.

Today we have more available methods for early detection of hearing loss even in newborns. Examination of these hearing screening (otoacoustic emissions, auditory brainstem response) should be performed as early as possible. Commonly screened newborns have risk factor for hearing loss, such as:

• Residence centers for intensive care to newborns from two or more days
• Syndromes that are known to lead to hearing loss (eg. Allport, Usher syndrome, syndrome Waardenburg)
• Family history of hearing loss,
• Congenital infections (eg. Toxoplasmosis, bacterial meningitis, syphilis, rubella, cytomegalovirus, herpes virus) and
• Craniofacial abnormalities (especially morphological abnormalities of the external ear).

This screen is called selective screening. Negative side of this screen is that it misses the affected children who have no risk factor. For these reasons it is best for all newborns to be screened whether there is or not a risk factor. This is the so-called universal screening.

Test methods of hearing
Depending on age, intellectual disability, the presence of other factors that will determine the level of co-operation applies appropriate test to assess hearing.

Children who have hearing disabilities, children who attend special schools and children who are at high risk of hearing loss is necessary once a year to estimate the hearing with any of these methods.

Hearing Disorders represent a significant social, medical and economic problem. It covers all age groups. It is estimated that, according to its significance, hearing damage takes the third place among the chronic health problems. The problem grows with age that connects to the normal processes of biological involution. So, epidemiological studies show that over 30% of people aged over 65 have moderate to severe hearing loss. This rate is certainly much smaller in younger age groups, which means that the problem as a whole is smaller. Namely, numerous studies have demonstrated that hearing loss at an early age leads to developmental disorders of speech and language, which prevents communication with the child, and it will negatively affect the social, emotional and intellectual development. Practice and extensive studies have shown that the use of early and timely rehabilitation measures, which are now available to anyone with impaired hearing, they correct hearing loss significantly, and thereby significantly contribute to improving the overall development of the child.

Among adults hearing loss affects quality of life. It leads to reduced ability to interact with the environment, hinder the acquisition of new knowledge and information, causing increased stress and unnecessary fatigue.

Most hearing impairments are managed via hearing aids. Based on audiometric trials, the lifestyle, the needs of the individual, individual selection is made and the instrument is adjusted.

The standard program for auditory rehabilitation which consists of providing information about opportunities and how to use the hearing aids, counseling for listening tactics, selection and setup of hearing aids, is performed by Audiologists and special educators.

All hearing instruments are designed to increase the volume of sounds arriving at the eardrum (membrane tympani), with the basic purpose of better understanding of speech. To achieve these hearing aids are made up of three main parts:

• Microphone - receiving acoustic energy (sound waves) and turns it into electricity
• Amplifier – processor - the electric signals amplified that makes them louder according to the individual hearing loss and
• Receiver - a small speaker, which converts electrical energy into acoustic energy again

Clogged hearing aid (BTE - Behind The Ear), the aid is placed behind the ear lobe and is associated with mold, it's silicone part that enters the ear and conducts sound from the device in the ear

Aid which occupies ear and the external auditory canal (ITE - In The Ear)

Aid that enters the ear canal and covers part of the ear (ITC - In The canal) and

Aid fully enters into the canal (CIC - Completely In The Canal).

What factors influence the choice of hearing aid?

Selecting the appropriate type of aid is based on several factors, which are grouped as physical factors and factors related to the hearing.

physical factors

1. The shape of the outer ear. E.g. if there is a deformation of the outer ear it is impossible to carry stewed aid.
2. Size and shape of the external ear canal. If the channel is narrow or bent can't be used ITC or CIC. Setting in such cases is difficult and uncertain (the appliance may fall over).
3. Manual skill. Removal and placement of channel devices, in particular the replacement of the battery and manipulating the control of the volume of some people is a particular difficulty.
4. Wax. In increased secretion of wax and increased moisture in the ear canal is no need for adequate ventilation. These people are not recommended canal hearing aids.
5. In case of a medical problem such as chronic ear infections do not recommend using the instrument that will completely close the ear canal. For these people it is important to allow ventilation using devices that do not fully close the ear canal. In this case they use airless devices connected to individual mold who has made more vent hole (hole that allows the passage of air).

1. Age. Channel types of hearing devices are unsuitable for small children because of the size of their ears and their rapid growth. Therefore there is a need for common preparation of a new shell, often leaving the child without hearing instruments. For this reason young children are recommended behind the ear hearing aids.
2. Factors related to hearing
   1. Audiometric shape of the curve. People who have damage to specific frequencies, not at all, for example preserved low frequencies (low, deep tones) and damaged high frequency (high, thin notes) best effects give those appliances that completely block the ear canal.
   2. Degree of hearing loss. In severe and most severe hearing impairments best result give BTE appliances, and also minimize the occurrence of feedback phenomenon (which is manifested by wheezing). Mild and moderate damage to successfully deal with both CIC and with BTE types of appliances.
   3. The specific features of individual hearing aids: directional microphone, telephone coil (small magnetic coil located in the appliance and allows better use of the phone) and other auxiliary devices, influence the choice of the instrument.
   4. Acoustic feedback or wheezing occurs when the microphone is close to the speaker. Sweltering aids have a clear advantage over the smaller channel types in relation to this phenomenon of feedback.

How often you need to adjust the hearing aids?

• Up to three years of age, every three months hearing should be checked, as well as the hearing instrument and mold.
• For children who are less than 6 months old, it is required that they have frequent controls for rapid growth and the mold needs to be changed.
• During the preschool years (from 3 to 6 years), the control should be done every 6 months unless there is a need of an earlier review (e.g. change in the hearing).

The cochlear implant is a small electronic device that provides the perception of sound in individuals with total deafness or very severe hearing impairment. The implant consists of an external part that is placed behind the ear and consists of:
Microphone which receives sounds from the environment.
Speech processor which selects and classifies the sounds received by the microphone
Transmitter and stimulator / receiver, receives the sounds from the speech processor and converts them in electrical impulses.

And the inner part that is a surgically implanted group of electrodes that collects the impulses from the stimulator and sends them to the acoustic nerve.

The implant cannot restore normal hearing but can help the person with hearing loss so the person receives a useful representation of sounds from the environment that will help him to understand speech.

Hearing aid amplifies sounds that damaged ear can't receive. While cochlear implant skips the damaged part of the ear and directly stimulates the acoustic nerve. The signals through the auditory nerve pathways are transmitted to the brain, where the signal is recognized as sound.
After implantation intensive rehabilitation is required, that will help the child to acquire speech, language and social skills.  Also adults who lost their hearing later in their life benefit from the cochlear implant. They need rehabilitation that will help them learn to link the sound signals received through the implant with sounds they remember. Usually it enables them to acquire the ability to understand speech through hearing only i.e. through the implant, without need to use the type as an aid to understand the speaker e.g. read ones lips.