Vestibulocochlear or VIII cranial nerve
The Vestibulocochlear nerve has two components, with the cochlear provides innervation to the hearing apparatus while the vestibular branch is concerned with balance. Conduction deafness results from interference with the transmission of sound waves in the external canal or middle ear to the organ of Corti. In sensorineural hearing loss, the lesion can be in the inner ear, the vestibulocochlear nerve or the brain. Because of the extensive bilateral connections of the ear, unilateral sensorineural hearing loss is usually due to lesion of the nerve nucleus or the nerve itself. Bilateral hearing loss can be either due to a central lesion or bilateral exposure to toxins and infectious agents.
• Auditory Component
o See if the child is wearing a hearing aid and remove it, while testing for hearing impairment.
o Examine the pinna and look for scars behind the ears.
o Do an otoscopic examination of both ears. Look for wax or other obstruction in the external auditory meatus and perforation of the tympanic membrane.
- Whisper test
The Whisper Test is a screening test for hearing loss in older children and correlates with a hearing loss of 30 decibels.
o Stand about two feet behind the child on one side so that they cannot read your lips.
o Place your finger on the external auditory meatus of the ear which is not being tested to mask the sound.
o At the end of your exhalation, whisper a word with two distinct syllables towards the ear which is being tested.
o Ask the child to repeat the two syllable word.
o Repeat the test on the other side
- Distraction test
It is a behavioural screening test of hearing for babies between six and eighteen months. The test capitalises on the infant’s instinct to turn and locate a quiet sound presented at ear level outside the visual field.
o In a quiet room, seat the baby on the parent’s lap facing forward.
o Ask a helper (this could be your examiner) to stand in front of the child capture his or her attention with a small toy.
o Stand behind the child on a horizontal level at 45º outside the baby's field of vision at one metre.
o Produce a sound stimulus with high frequency rattle and hissing sound.
o See if the child turns and looks around for the source of the sound
- Weber’s test (test for lateralization)
o Place the base of a vibrating 256 Hz tuning fork in the centre of the child’s forehead.
o Ask ‘on which side the sound is louder’. Normally it should be heard equally in both ears.
o If sensorineural deafness is present, the sound is heard better in the normal ear. In conductive hearing loss, the sound is louder in the abnormal ear.
- Rinne’s test
The Rinne test compares air conduction to bone conduction.
o Place the base of a 512 Hz vibrating tuning fork on the mastoid process, behind the ear.
o Ask the child to say "now", when they can no longer hear the ‘buzz’.
o When the child says "now", remove the fork from the mastoid...