Tone decay test is done for -

Tone decay test is a measure of nerve fatigue (i.e. neural deafness) and is used to detect retrocochlear lesions. A decay of more than 25 dB is diagnostic of retro cochlear lesion. Method of doing the test and principle: A continuous tone of 5 dB above threshold in 500 Hz and 2000 Hz is given to the ear and person should be able to hear it for 60 sec. The result is expressed as dB by which intensity has to be increased so that the patient car – hear the sound for 60 sec. If tone decay of >25 dB is present, it indicates retrocochlear leison e.g.—acoustic neuroma.