This nerve is responsible for hearing (cochlear part) and for equilibrium (vestibular part). Normally we test only the cochlear part.
1. The hearing of the patient can be tested by using a watch. First place the watch near one ear so that the patient knows what he is expected to hear. Next ask him to close his eyes and say so when he hears the ticking of the watch. The watch should be held away from the ear and then gradually brought towards it. The distance at which the sounds are first heard should be compared with the other ear.
In doing this test it must be remembered that loss of hearing can occur from various causes such as the presence of wax in the ear, or middle ear disease.
Nerve deafness can be distinguished from deafness due to a conduction defect (as in middle ear disease) by noting the following.
1. Sounds can be transmitted to the internal ear through air (normal way), and can also be transmitted through bone. Normally conduction through air is better than that through bone, but in defects of conduction the sound is better heard through bone.
2. Air conduction and bone conduction can be compared by using a tuning fork. Strike the tuning fork against an object so that it begins to vibrate producing sound. Place the tuning fork near the patients ear and then immediately put the base of the tuning fork on the mastoid process. Ask the patient where he hears the sound better. (This is called Rinne’s test). In another test the base of a vibrating tuning fork is placed on the forehead. The sound is heard in both ears but is more clear in the ear with a conduction defect (This is Weber’s test).
Defects in the vestibular apparatus or in the vestibular nerve are difficult to test and such cases need to be examined by a specialist.