Hearing loss is the partial or complete inability to perceive sound.Hearing canbe effected by different causes.The causes maybe congenital,traumatic,infective,neoplastic,degenerative,metabolic,ototoxic,vascular or autoimmune process.

Depending on the cause hearing loss canbe of 3 types:

1. Conductive hearing loss...results when sound from the outer ear to the inner ear cann't propagate normally.
2. Sensorineural hearing loss...results when transmission of sound to the brain fails.
3. Mixed hearig loss...caused by both of the factors causing conductive and sensorineural hearing loss.

Hearing loss canbe any of the five degrees depending on the severity as classified by WHO.

1. Mild
2. Moderate
3. Moderately severe
4. Profound
5. Total hearing loss

Hearing tests are performed in the conditions mentioned below.

1. Hearing impairment
2. As a part of routine assessment of child development
3. Maybe a part of general medical examination
4. Maybe used to know the cause of Tinnitus

Hearing of a person canbe tested by two methods.

• Clinical tests
• Audiometric tests

Clinical tests include finger friction test,watch test,speech tests,tuning fork tests.

Finger friction test:is a quick and rough method of testing hearing by rubbing the thumb and the finger close to the patients ear and ask if the sound is listened.

Watch test:is not done now but had been very popular befor the invent of audiometers.It's done by bringing a clicking watch close to the ear and measuring distance at which it is heard.

Speech tests:The patient stands at a distance of 6 meters from the examiner.The examiner says spondee words e.g white birds,blue sky or number with letters e.g 2AB and gradually walks towards the patient.The distance at which conversational & whispered voice are heard is measured.For clinical purposes 6m is considered normal for both conversational and whispered speech.Due to difference of intensity and pitch of sound of different examiners,this method is not a standard method. While performing the test eyes of the patient are covered to prevent lip reading,also the other ear is blocked.

Tuning fork tests:An ideal tuning fork for clinical use has frequency of 512Hz.With the help of tuning fork tets air conduction (AC) and bone conduction(BC) are examined separately.

To test AC a vibrating tuning fork is brought close to the external auditory meatus of patient at a distance of 2cm away and is held vertically.The sound waves reach to the inner ear transmitting through the tympanic membrane,middle ear and ossicles.It test the air conduction function of the ear. To test BC the foot plate of vibrating tuning fork is placed on the mastoid.The purpose is to stimulate only cochlea by vibrations conducting through the skull bone,mastoid.BC is a measure of cochlear function only.

Normally hearing through air conduction(AC) route is louder and heard twice as long as through bone conduction(BC) route.

The clinically useful tuning fork tests in the assessment of hearing are Rinne test,Weber test,Absolute bone production test(ABC tset),Schwabach test,Bing test & Gelles test. Rinne and Weber test are frequently done in combination.Rinne test can check conductive hearng loss.Weber test can check sensorineural hearing loss.

Rinne test:The examiner compares air conduction of the ear with its bone conduction  by changing the position of tuning fork.First,a vibrating tuning fork is placed on the patients mastoid bone that lies behind the ear.When the patient stops hearing the tuning fork sound,it's brought near to the meatus.If the patient can still hear it means AC is more than normal. A positive Rinne test is when AC is longer or louder than BC.It's observed in normal people and patients suffering from sensorineural deafness. A negative Rinne test (BC>AC) shows conductive deafness

Rinne test interpretation: Normal---AC >BC Rinne positive

Conductive deafness---BC >AC Rinne negative

Sensorineural deafness---AC >BC

Weber test:By weber test,lateralization of the sound is checked.A vibrating tuning fork is placed in the middle of the forehead.The patient is asked if he could listen the sound by both ears.Normally the sound is heard equally in both ears.The sound is lateralized to the worse ear in conductive deafness and is lateralized to the better ear in sensorineural deafness.It's to say that a patient with conductive hearing loss would listen the sound loudest in the effected ear and the patient with sensorineural hearing loss would hear the sound loudest in the uneffected ear.So weber test is the test of unilateral conductive hearing loss and unilateral sensorineural hearing loss.

Tuning fork interpretation: Normal case---sound is not lateralized

Conductive deafness---sound is lateralized to the poorer ear

Sensorineural deafness---sound is lateralized to the better ear

Audiometry is the measurement of the sense of hearing.An audiometer is an electronic machine that produces pure tones,the intensity of which canbe increased or decreased in 5db steps.A graph or audiogram is developed by this way that shows the hearing threshold.Different types of audiometric tests are:

Pure tone audiometry

Speech audiometry

Beckesy audiometry

Impedance audiometry

Pure tone audiometry: PTA is a quick,painless method of testing hearing problems resulting from acoustic injury,sudden hearing loss or rock and roll deafness.Generally air conduction thresholds are measured for tones of 125,250,500,1000 & 2000 and bone conduction thresholds for 250,500,1000,2000 &4000Hz.

The difference in the threshold of air and bone conduction(A-B gap) is a measure of the degree of conductive deafness. Pure tone audiometry determines the type and degree of hearing loss.

Speech audiometry:is the measurement of the patients ability to hear and understand speech.Two processed involved in speech audiometry are Speech reception threshold(SRT) and Speech recognition score.

SRT:The patient listens spondee words delivered to each ear through the headphone of an audiometer.SRT is the minimal intensity at which 50% of the words are repeated correctly by the patient.Normally SRT is witin 10db on average.

Speech recognition score:Also called word recognition score is a measure of patients ability to understand speech.

Bekesy audiometry:It's rarely performed these days.

Impedance audiometry:is an objective test in assessing hearing loss.It's very useful in children to test the hearing.The test consists of Tympanometry and Acoustic reflex measurements.Primarily impedance audiometry is done to determine the condition of tympanic membrane. Secondary function is to evaluate acostic reflex pathway.

Tympanometry reveals if the tympanic membrane has become stiffer,find function of eustachian tube in case of intact or perforated tympanic membrane.Tympanometry is based on simple principle that when a sound strokes tympanic membrane;some of the energy is absorbed while the rest is reflexed.A stiffer tympanic membrane would reflect more sound energy than a compliant one.

By changing the pressures in a sealed external auditory canal and then measuring the reflected sound energy  its possible to find the compliance or stiffness of the tympano-ossicular system and to know the condition of the middle ear.A graph  or tympanogram is drawn for compliance of tympano ossclar system against various pressure changes which help in diagnosing middle ear diseases.

Acoustic reflex is useful in testing hearing in children.It's also useful in detecting V111 nerve lesions,cochlear pathology,lesions of facial nerve and brainstem.