## 1 Introduction  
The eye is one of the most important organs of the human body, and the fundus, as an important part of the eye, has a large number of capillaries distributed on it, which are the only capillaries that can be directly observed non-invasively in the human body [1]. There is a close relationship between fundus health status and systemic diseases [2]. The fundus refers to the posterior tissues inside the eyeball, including structures such as the retina, macula, blood vessels, choroid, and optic nerve [3]. Medical research has shown that these structures are not only responsible for the formation and conduction of vision but also reflect the overall health of the body. For example, diabetes is a common systemic disease that causes retinal vasculopathy, which, in turn, leads to diabetic retinopathy [4]. High blood pressure can also cause changes in the blood vessels in the fundus, causing, for example, arteriosclerosis and retinal edema [4]. In addition, systemic diseases such as kidney disease, anemia, and leukemia can also be manifested through fundus lesions [5]. Many diseases in the human body will produce corresponding pathological changes to the retina of the fundus, and most patients have lesions in the fundus when the body has no obvious perception [6]. Some typical fundus lesion features are shown in Figure 1. The World Health Organization predicts that by 2030, the number of people with diabetic retinopathy will increase to 180.6 million, the number of people with age-related eye disease glaucoma will increase to 95.4 million, and the number of people with age-related macular degeneration will increase to 243.3 million [7]. Therefore, it is of great significance to make an early diagnosis of human health through fundus examination for the prevention and timely treatment of diseases. With the continuous development of technology, innovation, and upgrades, ophthalmic medical devices are also being updated, in which fundus cameras are specially used to capture fundus images, gradually replacing traditional ophthalmoscopy methods. Fundus cameras use a special imaging and illumination system to clearly capture the structures behind the eyeball, including the vitreous, retina, choroid, and optic nerve [8], providing objective fundus images, helping doctors observe changes in fundus lesions, and providing ophthalmologists with a more accurate and comprehensive diagnosis basis. Secondly, fundus cameras can also be used to compare the effects of treatments, evaluating the effectiveness of treatments by observing changes in fundus images. At present, desktop fundus cameras can obtain good quality fundus images and shorten the time of consultation, but there are also some disadvantages that cannot be ignored, such as the high price of equipment, high acquisition and maintenance costs, the need for them to be operated by doctors, and the requirement of extra training and guidancefor initial purchase. In addition, due to the complexity of the optical system and the large and heavy equipment, the camera is not suitable for mobile examination and follow-up use. It has not yet been widely used in all medical institutions, and only some large hospitals or specialized ophthalmic medical institutions can introduce and use such systems, which has high limitations. So, the main challenges in fundus camera design include the following:  
(1) Optical design: The optical design of the fundus camera is key, and needs to ensure that the camera can capture high-quality, high-resolution fundus images. Factors to consider when designing include the wavelength, intensity, and optimization of the optical path of the light source. At the same time, due to the physiological structure and optical  
Figure 1: Typical fundus lesion features (images are collated and taken from the web page [[https://ophth.dy.cn/article/501624](https://ophth.dy.cn/article/501624)]([https://ophth.dy.cn/article/501624](https://ophth.dy.cn/article/501624)), accessed on 2 January 2024).