# Correlation Between Sunlight Exposure Time and Cataract Prevalence in Korean Adults
## 1 Introduction  
Cataracts are one of the visual impairment diseases caused by the opacity of the lens of the eye. In addition, cataracts are a disease that commonly occurs in middle-aged and elderly adults among eye-related diseases. According to data from the Korea Centers for Disease Control and Prevention in 2012, the prevalence of cataracts in people over the age of 65 in Korea was 38.8% (31.0% for men and 44.3% for women), which was 13% higher for women than men. Moreover, Korea is showing the fastest aging rate in the world due to the improvement of health and nutrition along with the improvement of income levels. According to the National Statistical Office, the number of people aged 65 and over is expected to increase from about 8.15 million (17.8%) in 2020 to about 13.23 million in 2030, and about 17.81 million (about 40%) in 2040 (Korean Statistical information Service, 2020). Given the rapidly aging population of Korea, the incidence of cataracts is expected to continue to increase in the future. The mechanism of cataract formation is very complex and has been reported to be related to systemic diseases such as diabetes, as well as ultraviolet rays, heat, hormone abnormalities, and smoking [1]. Among them, exposure to sunlight containing ultraviolet (UV) rays is known to be an important factor in inducing cataracts both epidemiologically and experimentally [2; 3; 4]. Ultraviolet rays are divided into UV-C (100-280 nm), UV-B (280-315 nm), and UV-A (315-400 nm) according to biological characteristics, and areabsorbed by the lens of the eye [5; 6]. Human eyes cannot avoid constant exposure to sunlight [7]. Since the eye is a transparent tissue that is exposed to direct sunlight along with the skin, it has been reported to be related to eye aging [8]. In addition, cataracts have been reported to affect the clarity of the lens, cause vision and retinal dysfunction, and form due to changes in the structure and function of the lens epithelial cell membrane [9; 10; 11; 12]. WHO estimates that 20% of global blindness due to cataracts can be attributed to UV exposure. Avoiding direct sunlight during peak hours of UV-B has been suggested as a strong major preventive measure for cortical cataracts [13; 14]. Since sunlight contains UV rays, it may increase the risk of cataracts developing when overexposed to sunlight over an extended period of time [15]. One study found that males subjected to higher average annual UV levels were 1.36 times more likely to have more severe cortical opacities than male subjected to lower average UV levels [16]. Additionally, a study reported that the risk of cortical cataracts increased by 4.3% for each hour of outdoor activity [17]. Cataracts are defined as visual loss caused by the scattering of light on the lens. Changes in the Earth's atmosphere are expected to increase ultraviolet (UV) levels on the ground and adversely affect human health. These factors have been shown to have a significant relationship in epidemiological studies on animals and UV exposure experiments [18; 19; 20]. Sunlight entering Earth from the Sun is composed of electromagnetic waves of various wavelengths. In the vacuum of the upper atmosphere, it is composed of 50% infrared, 40% visible, and 10% ultraviolet light, with a total incident energy of about 1.4 kW/m\({}^{2}\)[21]. The notion that human exposure to ultraviolet wavelengths of sunlight is a factor in the development of cataracts has existed for many years, and good experimental evidence has been obtained for many years [22; 23]. This is because cell damage produced by ultraviolet light present in the external environment is likely to play an important role in disease development due to exposure to oxidative stress in the lens [24; 25]. [PERSON] et al. studied the relationship between outdoor activity and age-related cataract risk. In a population-based cross-sectional study of outdoor activity and age-related cataract risk in a rural population from July to September 2012, 883 adults (44.0% of participants) had a diagnosis of cataracts [17].