High dynamic range widefield fundus photography with transcranial illumination: a contrast agent-free method for non-mydriatic choroidal imaging.

The choroid, a critical vascular layer beneath the retina, is essential for maintaining retinal function and monitoring chorioretinal disorders. Existing imaging methods, such as indocyanine green angiography (ICGA) and optical coherence tomography (OCT), face significant limitations, including contrast agent requirements, restricted field of view (FOV), and high costs, limiting accessibility. To address these challenges, we developed a nonmydriatic, contrast agent-free fundus camera utilizing transcranial near-infrared (NIR) illumination. This system achieves a wide snapshot FOV of up to 185° eye-angle (130° visual-angle) without pharmacological pupillary dilation or contrast agents. By montaging two HDR images, the effective FOV can exceed 220° eye-angle (160° visual angle). Employing high dynamic range (HDR) imaging, the device ensures uniform contrast and enhanced choroidal visualization by correcting illumination inhomogeneity. The system demonstrated imaging performance comparable to ICGA when tested on healthy participants and patients with choroidal conditions, offering improved accessibility and affordability. This innovation holds promise for advancing the screening, diagnosis, and management of choroidal disorders, particularly in underserved settings.