Thickness distribution of fresh and preserved human eardrums measured with confocal microscopy.

HYPOTHESIS: In this study, the thickness distribution of the fresh human eardrum was measured and possible thickness changes in successive stages of preservation and preparation were studied.
METHODS: The thickness measurement was performed on axial fluorescence images taken perpendicularly through the membrane with a confocal microscope. The influence of fixation and preservation (in Cialit solution) on the thickness was also investigated. The same eardrum was prepared (decalcified, dehydrated, and stained) for histologic sectioning and the thickness was measured on the sections using conventional light microscopy.
RESULTS: Similar thickness distributions in the measured samples (n = 3) were observed. The pars tensa has a rather constant thickness in a central region curving as a horseshoe upward around the manubrium. The membrane thickens slightly from the inferior to the superior side. The anterior region is thicker than the posterior region. In narrow bands along the manubrium, peripheral rim, and in the region inferior to the umbo, a much larger thickness in comparison with that in the central region was found. Mean thicknesses of approximately 40, 50, and 120 microm were observed in the central region of the studied eardrums, respectively.
CONCLUSION: Whereas the thickness distribution of the human eardrums shows similar features, the absolute thickness seems to vary a lot from one specimen to another. There is no significant difference in thickness of the same membrane in fresh, fixed, or preserved condition. Thus, human eardrums may be safely preserved in fixative for later thickness measurements. The histologic preparation process, however, causes a significant location-dependent shrinkage.