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Abstract
The tympanic membrane (TM) separates the outer ear from the tympanic cavity. Repeated pathologies can permanently decrease its tension, inducing conductive hearing loss and adhesive processes up to cholesteatoma. The current main therapy is its surgical reconstruction. Even though lasers have been proposed to tighten atrophic TMs, details of this effect, specifically histological analyses, are missing. We therefore used laser pulses to induce TM collagen remodeling in an animal model to compare the histological and electrophysiological effects of different applied laser intensities before entering clinical studies. We irradiated Fuchsin-stained areas of the TM in anesthetized mice with 532-nm laser-pulses of 10mW for 30s (0.3J), 25mW for 30s (0.75J) or 50mW for 30s (1.5J) monitoring hearing with auditory brainstem responses (ABRs). The mice were sacrificed after 2 to 8 weeks and histologically analyzed. An increase in the TM thickness within the defined, stained, and irradiated areas could be observed after 4 weeks. Polarized light microscopy and transmission electron microscopy demonstrated the tissue volume increase majorly due to new collagen-fibrils. Directly after irradiation, ABR thresholds did not increase. We herein demonstrate a controlled laser-induced collagen remodeling within defined areas of the TM. This method might be the prophylactic solution for chronic inflammatory ear pathologies related to decreased TM tension.
Highlights
The tympanic membrane (TM) separates the outer ear canal from the middle ear.[1]
The maximal increase in TM thickness could be observed for the group of mice irradiated with 50 mW for 30 s (1.5 J) and sacrificed after 2 weeks
We present a preclinical study for a laser based collagen remodeling of the TM
Summary
The tympanic membrane (TM) separates the outer ear canal from the middle ear.[1] Its function is to collect the sound that has been transmitted through the ear canal, amplify it and transmit it further through the ossicular chain to the inner ear.[2,3]. The TM layer facing the outer ear canal is represented by the slightly keratinized epithelium (epidermal layer) and the subepidermal layer of loose connective tissue. The median layer, called lamina propria, is the collagen rich structure of the TM consisting of a radiar (external) and circular (internal) collagen layer. The predominant type of collagen within the pars tensa is collagen type II.[4] The TM layer facing the tympanic cavity consists of the monolayered epithelium (mucosal layer), which covers the tympanic cavity as well [Fig. 1(c)].5–8
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