Accuracy of Stereo Endoscope Calibrations for Forward and Oblique Optics

Accurate geometric calibration is a prerequisite for metric 3D reconstruction from stereo endoscopes, but practical deployment is complicated by non-standard optics (e.g., angled views), strong lens distortion, and clinically realistic image artifacts such as specularities and low texture. We present and evaluate calibration methods for a stereo endoscope with interchangeable 0∘ and 30∘ optics. We compare (i) a target-based calibration using an AprilGrid-style planar pattern and (ii) a reconstruction-based calibration approach that optimizes geometric consistency from image correspondences. To quantify calibration quality, we measure known distances on two reference objects. Our results demonstrate how calibration repeatability and optical-center stability directly impact the reliability of intraoperative distance measurements. Furthermore, this study provides practical recommendations on strategies to improve the reliability of intraoperative metric measurements.