Pure-tone audiometry ( PTA):-
The most generally useful technique which determines the subjects threshold of hearing for pure tones of several seconds duration . The pure tones delivered to the ear under test via suitadle earphone (AC) or by vibrator applied to the mastoid (BC) the frequency tested from (125 hz ---8000 hz ) and the intensities from ( -10 db to 120 db ) , by this curve we can see the type and degree of deafness in the graph .
Equilibrium ( balance ) :
It’s the function of the vestibular system , the detailed anatomy and physiology of this system is complex but can be divided to sensory part which consist of vestibular labyrinth , eyes and the somatosensory receptors in the muscles , joints and skin .
Those connected to brain stem , cerebellum and cerebrum , the labyrinthine function is respond to horizontal acceleration by utricle , angulary acceleration by semicirculer ducts and to linear acceleration by saccule.
Functional exa. Of the labyrinth :-
The function of laby. Can be evaluated by stimulating it artificially to produce nystagmus .
1- Caloric tests = If water at 30c or 44c , ie 7c abave and below normal body temp. is run into the ear under certain standerd condition nystagmus is produce in the normal person , the chnges in this normal graph indicat pathology .
2- Fistula test = The fistula in the bony wall of the horizontal semisarcular canal may result from cholesteatoma or tumour in the temporal bone , the compression of air in the ext. aud. Meatus lead to vertigo and nystagmus as soon as the vestibuler system still functioning .