Influence of Perspective Distortion in Laryngoscopy

Abstract

Objective: An experiment with controllable boundaries was designed to assess the influence of the recording angle and distance on two-dimensional (2D) imag-ing in laryngoscopy and resulting 2D parameter calculation derived from the glottal area waveform (GAW). Method: Two high-speed camera setups were used to synchronously record an oscillating synthetic vocal fold (VF) model, simulating a high-speed videoendo-scopy. One camera recorded at variable lateral recording angles and a reference camera in superior perspective. This was performed at different physiological recording distances and for two oscillation modes (with/without contacting VFs). The GAW was derived from the segmented glottis, and two parameters each for the categories of symmetry, periodicity, and closure were calculated, as well as two derivative measures. The percentage difference between the variable and reference camera value pairs was calculated, and the angle and height dependencies were quantified using linear regression. Results: The visual perception of a laryngoscopy was found to be influenced by the lateral recording angle, which may lead to misinterpretation of VF sym-metry among inexperienced observers. The strongest influence of recording angle was observed for symmetry parameters, the strongest being the Ampli-tude Symmetry Index with up to 2.6%/° (p