Tympanic membrane perforation descriptors and hearing levels in otitis media.

The air conduction threshold of hearing was determined at 0.5,1 and 2 kHz by manual audiometry on a consecutive series of young Thai adults with bilateral chronic suppurative otitis media. At the same time, after visual inspection of each tympanic membrane, the perforation was drawn, as faithfully as possible in respect of both shape and relative size, on a 40-mm diagram of a tympanic membrane. A study of the shapes of perforations showed that they could be described as elliptical, reniform or cardioid. For the purposes of calculating the area of a perforation, a reniform perforation was considered to be the result of substracting a smaller ellipse from a larger ellipse, which ellipses were in contact at the point of least curvature. The hearing threshold level was found to be a function of the size of the perforation. A power function best described this relationship. The relationship was such that a total perforation would be associated with a hearing loss of about 60 dB HL over the frequency range 0.5-2 kHz.