角膜曲率计的优化设计及实现

陈鹏, 王成, 郑刚, 等. 角膜曲率计的优化设计及实现[J]. 光电工程, 2019, 46(1): 180373. doi: 10.12086/oee.2019.180373
引用本文: 陈鹏, 王成, 郑刚, 等. 角膜曲率计的优化设计及实现[J]. 光电工程, 2019, 46(1): 180373. doi: 10.12086/oee.2019.180373
Chen Peng, Wang Cheng, Zheng Gang, et al. Optimization design and realization of a keratometer[J]. Opto-Electronic Engineering, 2019, 46(1): 180373. doi: 10.12086/oee.2019.180373
Citation: Chen Peng, Wang Cheng, Zheng Gang, et al. Optimization design and realization of a keratometer[J]. Opto-Electronic Engineering, 2019, 46(1): 180373. doi: 10.12086/oee.2019.180373

角膜曲率计的优化设计及实现

  • 基金项目:
    国家自然科学基金资助项目(61775140, 61378060)
详细信息
    作者简介:
    通讯作者: 王成(1977-),男,博士,副教授,主要从事生物医学光学与视光学方面的研究。E-mail:shhwangcheng@163.com
  • 中图分类号: TH773

Optimization design and realization of a keratometer

  • Fund Project: Supported by National Natural Science Foundation of China (61775140, 61378060)
More Information
  • 为实现简化的角膜曲率测量系统,提出一种以角膜反射成像为原理的角膜曲率计,其测量方法是将六个呈正六边形排布的点光源准直后投射到角膜前表面,角膜反射图像经物方远心光路成像在CMOS上;利用重心算法求出角膜反射图像中位于正六边形长对角线上的两个点光源的距离,进而求得角膜曲率。本文对系统的成像质量、测量范围和测量精度进行了理论分析,并且采用标准模拟眼和人眼进行实验,以验证理论分析结果。结果表明:本文设计的测量系统的角膜曲率半径测量范围为5.5 mm~11 mm(对应角膜屈光度30 m-1~60 m-1),测量误差为±0.02 mm。这将为自动角膜曲率计的设计及优化提供技术支持。

  • Overview: The paper summarizes previous research results on corneal curvature measurement. Based on previous studies, a simplified corneal curvature measurement system is proposed. The system uses the corneal reflection principle to measure the curvature radius of the corneal anterior surface. The specific measurement method employs six pointolites which arranged in a regular hexagon to emit parallel light to the surface of a cornea and are imaged by the cornea. Then the image is captured by a telecentric optical system in the object space to a CMOS camera. In order to obtain the corneal curvature, the distance between two pointolites located on the regular hexagonal diagonal in the corneal reflection images are calculated by using the center of gravity algorithm. We introduce the measurement range, measurement accuracy and other design indexes of the system, as well as the related parameters of the optical imaging system. We also performed image quality analysis of the imaging system. In the aspect of error analysis, we also made some theoretical analysis. We believe that the measurement error of the system is mainly determined by the accuracy of image algorithm to the image processing of corneal reflection, and we have given the theoretical calculation results in this aspect. We built a corneal curvature measurement system to further verify our theoretical analysis. We firstly calibrate the parameters of the system and then do repeated validation to get the repeated error. In addition, we measured the glass spheres with different curvature radius to verify that the system could accurately measure the curvature radius within the measurement range. Finally, we measured the corneal curvature radius of human eyes. The results showed that the system can quickly and accurately measure the corneal curvature radius of human eyes. We select the LED with a wavelength of 850 nm as the illumination source. The main consideration is that the near-infrared optical system can penetrate well. Although the human eye is not very sensitive to light at 850 nm, it has a certain effect on stabilizing the eye position of the test subject. In addition, the 850 nm LED process is mature, easy to obtain, and inexpensive. The whole optical system is simple, the device is few, the difficulty of assembly and adjustment is greatly reduced, and the imaging system adopts the object-distance optical path, which avoids the problem that the center of gravity of the image changes and the measurement result deviates.

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  • 图 1  系统原理图。(a)角膜曲率测量原理图;(b)测量光标排布示意图

    Figure 1.  Principle of the measurement system. (a) Principle of the corneal curvature measurement; (b) Arrangement of the measuring cursor

    图 2  成像光路原理图

    Figure 2.  Principle of the imaging system

    图 3  系统结构示意图。其中,①被测眼球;②准直透镜;③孔径光阑;④测量光标;⑤分束立方体;⑥固视灯;⑦, ⑧成像透镜;⑨光阑。图中标注的角度是平行光束与主光轴的夹角;图中只画出六个测量光标中的两个

    Figure 3.  The schematic illustration of the optical system. Where, ① Eye; ② Collimating lens; ③ Aperture; ④ Measuring cursor; ⑤ Beam splitting cube; ⑥ LED to fix eyes; ⑦ and ⑧ Cylindrical lens; ⑨ Stop. The marked angle numbers are intersection angles between the parallel light and the main optical axis. The figure shows only two of the six cursors

    图 4  结构设计图

    Figure 4.  The design structure of the optical system

    图 5  光学成像系统在不同曲率半径时对应的调制传递函数曲线。(a) R=5.5 mm; (b) R=7.18 mm; (c) R=11 mm

    Figure 5.  MTF curves of imaging system corresponding to different curvature radius. (a) R=5.5 mm; (b) R=7.18 mm; (c) R=11 mm

    图 6  光学成像系统在不同曲率半径时对应的场曲和畸变。(a) R=5.5 mm; (b) R=7.18 mm; (c) R=11 mm

    Figure 6.  Field curvatures and distortions curves of imaging system corresponding to different curvature radius. (a) R=5.5 mm; (b) R=7.18 mm; (c) R=11 mm

    图 7  光学成像系统在不同曲率半径时对应的点列图。(a) R=5.5 mm; (b) R=7.18 mm; (c) R=11 mm

    Figure 7.  Spot diagram curves of imaging system corresponding to different curvature radius. (a) R=5.5 mm; (b) R=7.18 mm; (c) R=11 mm

    图 8  角膜曲率半径和角膜反射像中位于六边形长对角线上的两个光点的距离的关系曲线

    Figure 8.  The relationship between the radius of curvature of the cornea and the distance between two points of light on the hexagonal diagonal in the corneal reflection image

    图 9  角膜反射图像。(a)模拟眼角膜反射图像;(b)人眼角膜反射图像

    Figure 9.  Corneal reflex image. (a) Corneal reflex image of artificial eye; (b) Corneal reflex image of human eye

    图 10  模拟眼测量结果

    Figure 10.  The results of simulated eye

    图 11  不同曲率的玻璃球的反射图像。(a) R=5.5 mm;(b) R=6 mm;(c) R=7 mm;(d) R=9 mm;(e) R=10 mm;(f) R=11 mm

    Figure 11.  Reflection images of a spherical mirror with different curvature. (a) R=5.5 mm; (b) R=6 mm; (c) R=7 mm; (d) R=9 mm; (e) R=10 mm; (f) R=11 mm

    表 1  系统所用器件参数及间距(或透镜厚度)

    Table 1.  Parameters and their intervals of the elements used in the optical system

    器件 参数 间距或透镜厚度
    准直透镜 f=65 mm,Φ=6 mm a=1 mm, b=65 mm
    孔径光阑 Φ=1.0 mm
    测量光标 λ=850 nm
    分束立方体 分光比1:1 c=115 mm, d=25.4 mm
    固视灯 Φ=2 mm e=15 mm
    成像透镜1 f ≈200 mm, Φ=25.4 mm f=90 mm, g=6.1 mm
    成像透镜2 f ≈60 mm, Φ=25.4 mm h=120 mm, i=11.4 mm
    光阑 Φ=6 mm j=33 mm, k=23 mm
    下载: 导出CSV

    表 2  角膜曲率测量系统在不同曲率半径R所得到的正六边形长对角线上的两个光点的距离L

    Table 2.  The distance (L) of two points on a regular hexagonal diagonal in the corneal curvature measurement system obtained under different curvature radius (R)

    R/mm 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11
    L/mm 0.429 0.465 0.5 0.534 0.569 0.602 0.636 0.669 0.701 0.733 0.765 0.796
    下载: 导出CSV

    表 3  角膜曲率测量系统在不同曲率半径处的测量精度

    Table 3.  Measurement accuracy (A) of corneal curvature measurement system at different radius of curvature (R)

    R/mm 5.5 7.18 7.8 8.7 11
    A/m-1 0.056 0.034 0.029 0.024 0.016
    下载: 导出CSV

    表 4  玻璃球曲率的测量结果

    Table 4.  Results of curvature of glass sphere

    已知半径/mm 本系统测量值/mm
    5.5±0.02 5.5±0.02
    6±0.02 6.02±0.01
    7±0.02 6.99±0.02
    9±0.02 8.98±0.02
    10±0.03 10.01±0.02
    11±0.03 11.01±0.02
    下载: 导出CSV

    表 5  两种仪器所测的角膜曲率半径比较

    Table 5.  Comparison of corneal curvature measured by two instruments

    IOL-Master测量值/mm 本系统测量值/mm
    7.8±0.02 7.8±0.02
    7.88±0.01 7.87±0.02
    8.61±0.01 8.62±0.02
    8.71±0.02 8.7±0.02
    7.85±0.01 7.85±0.02
    7.83±0.02 7.84±0.02
    7.73±0.01 7.74±0.01
    7.82±0.01 7.83±0.01
    7.84±0.02 7.84±0.02
    7.71±0.02 7.71±0.02
    下载: 导出CSV
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出版历程
收稿日期:  2018-07-13
修回日期:  2018-09-13
刊出日期:  2019-01-01

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