针对小动物眼底成像的光学相干层析成像系统

： Small animal models are essential for ophthalmic research because they enable controlled investigation of disease mechanisms and preclinical evaluation of new therapies. Optical Coherence Tomography （OCT） is a noninvasive， high-resolution imaging modality widely used for in vivo visualization of retinal microstructures. However，most OCT systems for small-animal fundus imaging are adapted from human-eye platforms and do not fully accommodate the anatomical and optical characteristics of small animal eyes. In particular，the much smaller pupil diameter of small animals makes wide-angle scanning highly susceptible to beam clipping and field restriction. A major cause of this limitation is the spatial separation of the pivot points associated with two orthogonal scanning directions in traditional galvanometric scanners. This study aimed to develop a dedicated OCT scanner for small-animal fundus imaging by integrating a 4f system into the sample arm to eliminate pivot-point separation and improve pupil matching. The optical characteristics of human and small-animal eyes were first analyzed，focusing on pupil size and its effect on beam transmission during scanning. Then，two OCT sample-arm configurations were compared using optical simulation software： a traditional scanner consisting of a two-dimensional galvanometer and a telescope，and a proposed scanner composed of two one-dimensional galvanometers，a 4f system，and the same telescope. In the proposed scanner，the 4f system relayed the beam deflections of the orthogonal galvanometers and mapped their pivot points onto the same spatial location，thereby removing the pivot-point separation of the traditional scheme. Simulations were performed with a Gaussian input beam，and galvanometer deflection angles were set within − 8° to 8° to visualize beam propagation， pivot positions， and retinal spot distributions. For experimental validation， a SD-OCT system was constructed. Comparative in vivo retinal imaging was performed in a guinea pig using the same OCT platform alternately configured with the traditional and proposed scanners. The maximum scanning angle of the proposed scanner was also estimated in air by geometric-optics measurement based on beam displacement on a screen. Optical simulations showed that the traditional scanner exhibited a clear separation between the pivot points of the two scanning directions，with a distance of 5.8 mm. When one pivot point was aligned with the pupil plane，the beam corresponding to the other scanning direction was partially blocked by the small pupil，resulting in asymmetric beam transmission and an elliptical retinal Field of View （FOV）. In contrast，the proposed scanner successfully merged the two pivot points through the 4f system，enabling the unified pivot to coincide with the pupil plane and maximizing pupil utilization. The simulated maximum entrance pupil angle reached 56.0°. Experimental results were consistent with the simulations. The measured full scanning angle in air was 56.7°. In vivo guinea pig imaging further demonstrated the superiority of the proposed scanner. Whereas the traditional scanner produced an elliptical field with limited retinal coverage，the proposed scanner generated a larger and more regular circular FOV. The in vivo results further showed reduced edge truncation，alleviated signal cutoff caused by pupil obstruction，and broader visualization of retinal structures. These findings confirmed that the 4f-based design effectively overcame the field limitation induced by pivot-point separation in traditional systems. A dedicated OCT scanner for small-animal fundus imaging was developed and validated by integrating a 4f system into the sample arm. By eliminating the separation between orthogonal scanning pivot points and aligning the merged pivot with the pupil plane，the proposed scanner mitigates beam clipping caused by the small pupils of animal eyes. Both simulation and in vivo experiments demonstrated that，compared with a traditional scanner，the proposed system achieves a substantially larger and more regular retinal FOV， with a maximum entrance pupil angle of 56.0°. This work provides a practical and effective solution for wide-field OCT imaging of small-animal fundi.