## 2 Methods and Design
### Design of the Fundus Illumination System
#### 2.3.1 Illumination Source Selection and Theoretical Calculation  
The human eye does not emit light, so it was necessary to choose a light source with the appropriate wavelength band. Figure 6a shows the spectral transmittance curve jointly studied by the U.S. Department of Industry and Hygiene, the University of Michigan, and the U.S. Department of Ophthalmology [21]. The four curves in the figure represent the spectral transmittance of different wavelengths of light through the anterior chamber, lens, vitreous, and retina. The wavelength is in the range of 450 to 800 nm and the transmittance of each tissue is above 75%. Since the fundus tissue has a low effective reflectance of 0.1-0.001%, it is necessary to increase the irradiance of the illumination light in order to obtain a strong fundus-reflected light; the longer the wavelength of the incident light, the higher the reflectivity of the fundus tissue. It has a reflectivity of about 2% for yellow-green light at a wavelength of 550 nm and a reflectance of more than 10% for near-infrared light at 750 nm [12]. The reflectivity is relatively high, making it easier to obtain retinal images. However, the results of clinical medical testing showed that the resolution of fundus imaging is different under different wavebands. The design and development of a new fundus camera [12] by [PERSON] of the University of Chinese Academy of Sciences showed the results of fundus hyperspectral imaging, as shown in Figure 6b, from which it can be seen that compared with the near-infrared band, the resolution of fundus imaging images under visible light is higher. Therefore, in this study, visible light was chosen as the source of illumination. Figure 7a shows the spectrum of a white LED light source. Figure 7b shows the spectrum of full-spectrum white LED. White LED with high blue light will cause some  
Figure 6: (**a**) Spectral transmittance of human eye tissues (the spectral transmittance curve jointly studied by the U.S. Department of Industry and Hygiene, the University of Michigan, and the U.S. Department of Ophthalmology in 1962). (**b**) Fundus hyperspectral imaging results [12]. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**No.** & **Surface Type** & **Radiums/mm** & **Thickness/mm** & **Material** & **Diameter** & **Cone Coefficient** \\ \hline
1 & Even Asphere & 29.767 & 5.678 & D-FK61 & 10.015 & \(-\)5.388 \\
2 & Even Asphere & \(-\)18.797 & 0.099 & & 10.015 & 0.296 \\
3 & Standard & 53.340 & 3.842 & D-ZPK5 & 10.197 & 0.000 \\
4 & Standard & \(-\)28.667 & 0.100 & & 10.197 & 0.000 \\
5 & Standard & \(-\)31.440 & 9.774 & H-ZF62 & 10.162 & 0.000 \\
6 & Standard & 23.192 & 0.100 & & 10.162 & 0.000 \\
7 & Even Asphere & 12.750 & 10.001 & H-ZF73 GT & 12.717 & \(-\)0.935 \\
8 & Even Asphere & 13.382 & 4.999 & & 12.717 & 0.543 \\ IMA & Standard & Infinity & - & 10.740 & 0.000 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Lens data of imaging system. damage to the human eye. Full-spectrum white LED has a more continuous and uniform spectral distribution, which can provide a more natural lighting effect, and the color rendering index is higher, but the blue light is still high and the red light is higher. The solar spectrum LED with low blue light and high CRI reduces blue light damage to the human eye and is more suitable for fundus lighting. In addition, the reflection ratio of the fundus to green light is high and the high proportion of green light will improve the contrast of the fundus image, which can more accurately restore the true color of the object. Therefore, a violet light excited the solar spectrum LED light source for fundus illumination.