[1] [1] Wan Mingmei. Ophthalmology/Technology for visually handicapped students［M］. Taibei: Wu-Nan Book Company Ltd., 2004: 3-5.

[3] [3] Liu Zuguo, Lin Yuesheng. Corneal topography［M］. Guangzhou: Guangdong Science and Technology Press, 2001: 1-3.

[4] [4] Sui Chenghua, Wo Shengjie, Gao Nan, et al. Design and implementation of imaging system for corneal topography based on Placido disk［J］. Acta Optica Sinica, 2016, 36(12): 1222001.

[5] [5] Huang Hailong, Wang Hong, Ji Li. Order morphology edge detection algorithm based on partial fuzzy enhancement［J］. Chinese Journal of Scientific Instrument, 2012, 33(11): 2608-2614.

[6] [6] Zhang Wenjie, Xiong Qingyu, Shi Weiren, et al. Weighted neighbor-region based multi-level fuzzy edge detection method［J］. Journal of Jilin University (Engineering and Technology Edition), 2015, 45(3): 998-1004

[7] [7] Shi Wen, Zhu Xuefang, Zhu Guang. A daptive edge detection algorithm of MRI image based on morphology［J］. Chinese Journal of Scientific Instrument, 2013, 34(2): 408-414.

[8] [8] Zhang Zhilong, Yang Weiping, Li Jicheng. A novel salient image edge detection algorithm based on ant colony optimization［J］. Journal of Electronics & Information Technology, 2014, 36(9): 2061-2067.

[9] [9] Wang Sheyang, Song Shenmin, Chen Xinglin, et al. Improvement spatial moment subpixel edge detection method［J］. Journal of Harbin Institute of Technology, 2006, 38(6): 870-876.

[10] [10] Wu Peng, Xu Hongling, Song Wenlong, et al. A nonlinear quartic image interpolation based subpixel edge detection algorithm［J］. Journal of Harbin Engineering University, 2015, 36(2): 243-247.

[11] [11] Gong D W, Chen J H, Yuan C, et al. A new method for reconstruction of corneal topography with Placido disk system［J］. Advanced Materials Research, 2014, 974: 373-378.

[12] [12] Doss J D, Hutson R L, Rowsey J J, et al. Method for calculation of corneal profile and power distribution［J］. Archives of Ophthalmology, 1981, 99(7): 1261-1265.

[13] [13] Klyce S D. Computer-assisted corneal topography. High-resolution graphic presentation and analysis of keratoscopy［J］. Investigative Ophthalmology & Visual Science, 1984, 25(12): 1426-1435.