Assessment of Hearing - Otolaryngology

What are the three types of hearing loss? 1. Conductive hearing loss – It is caused by any disease process that interferes with the conduction of sound from external ear to the stapediovestibular joint. The cause may lie in the external ear or the Eustachian tube in the form of obstructions or in the tympanic membrane in the form of perforation or in the middle ear in the form of fluids or in the ossicles in the form of fixation or disruption. 2. Sensorineural hearing loss - This is caused by lesions of the sensory type of the cochlea or of the cranial nerve 8 and its central connections of the neural type. When the hearing loss is due to lesions of cranial nerve 8, it is known as retrocochlear and when it is because of the lesions of the central auditory connections, it is referred to as central deafness. 3. Mixed hearing loss – In this kind of hearing loss, both sensorineural and conductive elements of deafness are present in the same ear. There is an air-bone gap that indicates the conductive element and impairment of bone conduction that triggers sensorineural loss. Mixed hearing loss is found in cases of chronic suppurative otitis media and otosclerosis. What four factors are important while assessing the auditory functions? 1. Type of hearing loss – whether it is conductive, sensorineural or mixed. 2. Cause of hearing loss – it may be congenital or traumatic or it could be infection or an auto-immune process. 3. Degree of hearing loss – It could be mild or moderate or it could be severe or total. 4. Site of the lesion – If it is conductive hearing loss, the lesion may be at the external ear or the tympanic membrane or it could be at the middle ear or the Eustachian tube. Tympanometry is helpful in finding the site of lesions. If it is a sensorineural loss, it is to be determined whether the lesion is cochlear or central or retrocochlear. Often special tests of hearing are needed to differentiate the types of these lesions. How is hearing tested? It is done through clinical or audiometric tests. What are the four major clinical tests of hearing? 1. Finger Friction Test – It is a quick method of screening and it involves rubbing and snapping the thumb and a finger by positioning them close to the ear of the patient. 2. Watch Test – A watch that clicks is brought close to the ear of the patient and the distance at which it is heard is measured. 3. Speech or Voice Tests – For the purpose of the test, the patient has to hear a conversation at a distance of forty feet in quiet surroundings. Its disadvantage is the lack of standardisation in intensity. 4. Tuning Fork Tests – They are done with tuning forks of different frequencies. The average frequency is 512 Hz. The tuning fork is activated by striking it gently against the examiner’s elbow or heel of hand. Tuning forks of lower frequencies than 512 Hz produce sense of bone vibration. A vibrating fork is placed vertically in line with the meatus to test air conduction and it is kept about two centimetres away from the opening of the external auditory canal. The sound waves are transmitted through the tympanic membrane. Middle ear and the ossicles to the inner ear. In order to test bone conduction, the foot plate of the vibrating tuning fork is placed on the mastoid bone. Cochlea is stimulated directly by the vibrations conducted through the skull bones. What are some of the important and clinically useful tuning fork tests? 1. Rinne – Air conduction of the ear is compared with its bone conduction. A vibrating tuning fork is placed on the patient’s mastoid and when hearing stops, it is brought besides the meatus. If he still hears, air conduction is more than bone conduction. Rinne’s test can be concluded as false negative in severe unilateral sensorineural hearing loss. The patient does not hear any sound of the tuning fork by air conduction but responds to bone conduction. 2. Weber’s – A vibrating tuning fork is placed in the middle of the forehead and the patient is asked in which ear he or she can hear the sound. Normally, it is heard equally in both ears. It is lateralized to the worse ear in conductive deafness and to the better ear in sensorineural deafness. 3. Gelle’s – It is a test of bone conduction and examines the effect of increased air pressure in ear canal on hearing. It is performed by placing a vibrating tuning fork on the mastoid while changes in air pressure in ear canal are brought about by Siegel’s speculum. What are the four types of audiometry tests and explain briefly, giving details about tympanometry as part of impedance test 1. Pure Tone Audiometry- Audiometer is used to produce pure tones, Their intensity can be increased or decreased by 5 dB steps and the amount of intensity that has to be raised above the normal level is a measure of the degree of hearing impairment at that frequency. It is charted in the form of a graph called audiogram. It is used to measure the degree and type of hearing loss, prescription of hearing aid and degree of handicap for medico-legal purposes 2. Speech Audiometry- The patient’s ability to hear and understand speech is measured. The two parameters used are speech reception threshold and discrimination score. 3. Bekesy Audiometry- It is a self-recording audiometry where various pure tone frequencies automatically move from low to high while the patient controls the intensity through a device that indicates Type 1 – Type V degree. 4. Impedance Audiometry- There are two tests that make up this category. They are tympanometry and acoustic reflex measurements. Tympanometry is based on a simple principle that dwells on when a sound strikes the tympanic membrane; some of its energy is absorbed while the remainder is reflected. It helps in finding the degree of compliance or stiffness of the tympanic membrane to show the health of the middle ear. Five types of tympanograms are Type A, Type As, Type AD, Type B and Type C with the range being Type A as normal and Type C as maximum compliance.