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摘要:目的
针对传统便携式免散瞳眼底相机存在照明与成像光路相互制约、角膜杂散光干扰严重、视网膜不同区域难以同时清晰成像等问题，本文提出一种新型眼底光学系统设计方案。
方法该方案采用四点光源矩形布局与分区域亮度可调的照明方式，在3.2 mm瞳孔直径下使角膜杂散光较传统方法减少91.56%，并可实现视盘与黄斑区域的高对比度同步成像。系统通过照明光路与成像光路分离设计，结合线栅与液晶叠层偏振技术，有效抑制光学表面反射杂光。
结果在230.4 mm*90 mm紧凑型结构内同步实现53°大视场、±20 D屈光补偿，及6 μm的眼底分辨率。
结论本系统通过单次拍摄人眼即可获得视盘与黄斑细节清晰、对比度优良的视网膜图像。
Abstract:Objetive: To address the inherent limitations of conventional portable non-mydriatic fundus cameras, including the mutual constraints between illumination and imaging optical paths, severe interference from corneal stray light, and the difficulty of achieving simultaneous clear imaging of different retinal regions, this paper proposes a novel fundus optical system design. Method: The proposed system adopts a four-point rectangular illumination layout combined with regionally adjustable illumination intensity. At a pupil diameter of 3.2 mm, the corneal stray light is reduced by 91.56% compared with traditional approaches, enabling high-contrast synchronous imaging of both the optic disc and macular regions. Furthermore, a separated illumination and imaging optical path architecture is employed. By integrating a wire-grid polarizer with a stacked liquid-crystal polarization scheme, stray light caused by optical surface reflections is effectively suppressed. Result: Within a compact system envelope of 230.4 mm × 90 mm, the proposed fundus camera simultaneously achieves a wide field of view of 53°, a refractive error compensation range of ±20 D, and a retinal spatial resolution of 6 μm. Conclusion: The proposed system enables the acquisition of high-contrast retinal images with clearly resolved details of both the optic disc and macula in a single-shot capture, demonstrating its suitability for portable non-mydriatic fundus imaging applications.
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图 1 新型便携式眼底相机系统原理图
Figure 1. Schematic diagram of the proposed portable fundus camera system.
图 2 四点光源排布及其照度分析。(a) 四点光源在瞳孔上的几何排布；(b)眼底的照明区域示意图
Figure 2. Four-point light source configuration and illuminance analysis. (a) Geometric arrangement of the four-point light sources on the pupil plane; (b) Schematic illustration of the illuminated region on the fundus.
图 3 网膜物镜设计结果。(a) 网膜物镜结构；(b) 网膜物镜MTF曲线。
Figure 3. Design results of the retinal objective. (a) Optical layout of the retinal objective; (b) MTF curves of the retinal objective.
图 5 不同光源布局照明仿真结果对比分析：(a)两点对称照明瞳孔面光场分布；(b)四点矩形照明瞳孔面光场分布；(c)两点对称照明眼底面照度分布；(d)四点矩形照明眼底面照度分布；(e)两点对称照明下传感器接收的角膜杂散光分布；(f)四点矩形照明下传感器接收的角膜杂散光分布。
Figure 5. Comparative analysis of illumination simulation results for different light source configurations. (a) Intensity distribution on the pupil plane under two-point symmetric illumination; (b) Intensity distribution on the pupil plane under four-point rectangular illumination; (c) Irradiance distribution on the fundus plane under two-point symmetric illumination; (d) Irradiance distribution on the fundus plane under four-point rectangular illumination; (e) Distribution of corneal stray light received by the sensor under two-point symmetric illumination; (f) Distribution of corneal stray light received by the sensor under four-point rectangular illumination.
图 6 成像系统像质评价：(a) 0 D下可见光波段的调制传递函数曲线；(b) ±20 D范围内各视场在子午方向上、166.67 lp/mm处的光学传递函数模值；(c) ±20 D范围内各视场在弧矢方向上、166.67 lp/mm处的光学传递函数模值。
Figure 6. Image quality evaluation of the imaging system. (a) MTF curves in the visible wavelength range at 0 D; (b) Magnitude of the optical transfer function (|OTF|) at 166.67 lp/mm in the tangential direction for different fields within a refractive error range of ±20 D; (c) Magnitude of the optical transfer function (|OTF|) at 166.67 lp/mm in the sagittal direction for different fields within a refractive error range of ±20 D.
图 8 人眼成像测试：(a)对称两点照明成像；(b)四点矩形照明成像；(c)常规均匀照明的视网膜图像，其中(c1)视盘区域、(c2)黄斑中心凹、(c3)血管对比度局部（沿图中黄色截线所示）；(d)区域调光后的视网膜图像，其中(d1)视盘区域、(d2)黄斑中心凹、(d3)血管对比度局部（沿图中黄色截线所示）。
Figure 8. Human eye imaging experiments. (a) Retinal image acquired under two-point symmetric illumination; (b) Retinal image acquired under four-point rectangular illumination; (c) Retinal image acquired under conventional uniform illumination, with (c1) the optic disc region, (c2) the foveal center, and (c3) a local profile of vascular contrast along the yellow line indicated; (d) Retinal image acquired with regionally adjusted illumination, with (d1) the optic disc region, (d2) the foveal center, and (d3) a local profile of vascular contrast along the yellow line indicated.
表 1 眼底相机的设计技术指标
Table 1. Design specifications of the fundus camera.
技术指标 数值 总长（mm） ≤200 视场角（deg） ≥53 入瞳直径（mm） 2 工作波长（nm） 436~656/850 调焦度数范围（D） -20~+20 调制传递函数（MTF） @166.67 lp/mm ≥0.2 
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表 2 本系统与国内市面上两款相机的性能参数对比
Table 2. Comparison of performance parameters between the proposed system and two commercially available domestic fundus cameras.
工作参数 本系统 AI-FD16aF Kestrel 300 入瞳直径 (mm) 3.2 3.5 3.5 工作距离 (mm) 35±2 - 15±5 分辨率 (lp/mm) ≥80 80 ≥60 视场角 (°) 53 40 35 屈光调节范围 (D) −20~+20 −15~+15 −15~+15 照明方法 四点矩形 单点倾斜照明 单点倾斜照明 尺寸（长*高）（mm*mm） 230*90 280*130 284*145
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