<prompt> Gelles phenomenon is absent in -CSOMTympanosclerosisMenieres diseaseOtosclerosis  <response>: Gelles test compares intensity of bone conducted tuning fork sound without and with raising pressure on the tympanic membrane with Siegels speculum.Normally,Gelles test is positive because intensity of hearing decreases when air pressure is raised in external auditory canal.In ossicular fixation or ossicular discontinuity,increased air pressure makes no changes in the sound intensityGelles negative REF.Diseases of EAR,NOSE and THROAT Ref:PL Dhingra 6th Edition page no.447 