Microanatomic analysis of the round window membrane by white light interferometry and microcomputed tomography for mechanical amplification.

OBJECTIVE

The round window membrane (RWM) is increasingly becoming a target for amplification using active middle ear implants. However, the current strategy of using available transducer tips may have negative consequences for the RWM. We investigated the microanatomy of the RWM to establish a basis for the design of the transducer tip for the RWM driver.

STUDY DESIGN

Using the guinea pig as an animal model, microcomputed tomography (μCT) and white light interferometry were used to study the topography of the RWM and RW niche (RWN). The curvatures of the RWM surface were calculated using the topography data.

MAIN OUTCOME MEASURES

The 3-dimensional structure of the scala tympani terminal, saddle-shaped surface topography, and surface curvature were determined.

RESULTS

The size of the scala terminal was approximated as an ellipse for which the major and minor axes were 1.29 and 0.95 mm. The average minimum and maximum radii of curvature around the center of RWM were -0.44 and +0.70 mm along the minor and major axis.

CONCLUSION

The microanatomies of the RWM and RWN have important implications for the design of the transducer tip to maximize energy transfer while minimizing its distortion and permanent disruption. Our results suggest that the size of the transducer tip should be smaller than the minor axis of the scala terminal to avoid collision with the RWN. The driver should be designed to conform to the topography and radius of curvature of the center portion of the RWM, which for a guinea pig is 0.44 mm.