Design of a fisheye arthroscope with an ultra-wide field of view for viewing joints

The field of view (FOV) is a critical parameter in optical endoscopic systems that directly influences a physician's ability to inspect internal anatomical structures thoroughly and accurately without repositioning the device. This study designs and optimizes a rigid arthroscope equipped with a fisheye lens to achieve an ultra-wide 200° field of view, thereby enhancing joint visualization. The fisheye lens is specifically redesigned and optimized to function as the objective lens, and a gradient-index (GRIN) rod is employed to relay the image from the objective to the eyepiece. The device is optimized for the short working distances of arthroscopy, while its ~0.7-500 mm refocusing range (via minor eyepiece adjustment) also makes it adaptable to endoscopic applications that require longer working distances. Image-quality metrics are used to evaluate aberrations, particularly those caused by the increased viewing angle. While wide viewing angles typically amplify off-axis aberrations, the optimized design reduces and balances these residuals to preserve high image quality, and its performance is benchmarked against a high-definition arthroscope featuring a 70° field of view. Overall, the fisheye arthroscope achieves a substantially wider field of view, with aberrations deliberately balanced so that RMS spot sizes remain below the Airy disk, thereby enhancing visualization during clinical joint examinations.