Correlation Between Sunlight Exposure Time and Cataract Prevalence in Korean Adults

Abstract

This study analyzed the survey data of the ophthalmic examination of the 5th National Health and Nutrition Examination Survey to investigate the relationship between the prevalence of cataracts in Koreans and exposure to sunlight in daily life. From January to December, 952 people in 192 districts were classified into a 2–5 h group and a group of more than 5 h of sunlight exposure, and statistical analysis using SMS version 26, including the chi-square test and logistic regression analysis, was conducted. Results: The gender difference was that women had a higher incidence of cataracts when the exposure time to sunlight was 2 to 5 h (46.7% for men, 53.3% for women, p < 0.001) and men had a higher incidence of cataracts when it was more than 5 h (62.3% for men, 36.8% for women, p < 0.001). The incidence increased significantly after age 45 for the groups of both 2 to 5 h (65.8% for men, p < 0.001) and 5 h or more (80% for p < 0.001) of sunlight exposure. In the group with 2 to 5 h of sunlight exposure, the prevalence of cataracts was high in people living in large cities, such as 52 people in Seoul (10.8%) and 63 people in Busan (13.1%), while in the group with 5 h or more, the incidence of cataracts was significantly higher in people living in rural areas, such as 36 people in Gangwon Province (7.7%) and 85 people in North Gyeongsang Province (18.1%). Through this, it was confirmed that Koreans had a higher incidence of cataracts when exposed to sunlight for more than 5 h, and differences according to socio-demographic characteristics could be identified in the case of a sunlight exposure time of 2 to 5 h or more.

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 are absorbed 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/m² [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].

Tang Y 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].

A study by Li X et al. analyzed the correlation between sunlight and cataracts through a meta-analysis and showed that sunlight exposure was associated with a slightly higher risk of cortical cataracts in three types of cataract [15].

Lawrence et al. examined the relationship between cataract prevalence, altitude, and sunlight hours in a large, national probability sample survey conducted in 105 districts of the Himalayan Kingdom of Nepal from December 1980 to April 1981. Age- and gender-standardized cataract prevalence was 2.7 times higher in areas below 185 m than in areas above 1000 m. Cataract prevalence showed a negative correlation with altitude (r = −0.533, p < 0.0001). However, there was a significant correlation between cataract prevalence and sunlight. A positive correlation was observed between the two (r = 0.563, p < 0.0001). Areas with an average of 12 h of sunlight had 3.8-times more cataracts than areas with an average of 7 h of sunlight [26].

As mentioned earlier, various factors forming cataracts have been reported in previous studies. In addition, based on the results of previous studies that sunlight is significantly associated with cataract prevalence, this study aimed to analyze various demographic factors such as gender, age, educational background, and region, focusing on the sunlight exposure time and cataract prevalence in Korean adults.

As mentioned earlier, various factors that form cataracts have been reported in previous studies. Many people are well aware that sunlight causes skin problems. As previous studies dealing with sunlight exposure and cataract prevalence reported, it can be seen that the eye is an organ that is vulnerable to damage caused by sunlight. However, only about 7% of the organization understands the association between ultraviolet rays and eye problems [27]. Considering these points, this study aimed to analyze the analysis by cataract type (cortical, nuclear, anterior subcapsular, posterior subcapsular) and various demographic factors such as gender, age, educational background, and region, focusing on the sunlight exposure time and cataract prevalence of Korean adults.

While the latest technology is a study using optical technology, the purpose of our study was to assess a large national population group. In addition, we hope that it will provide data for reviewing the role of the optical industry to prepare for UV protection to protect the eyes from sunlight, and we will use these basic data for epidemiological research on cataract prevention when examining the eyes using top-notch technology in the ophthalmology field.

2. Materials and Methods

2.1. Subject

In order to confirm the correlation between the prevalence of cataracts and sunlight in Koreans, this study conducted an analysis of the 5th National Health and Nutrition Survey (2019) conducted by the Korea Centers for Disease Control and Prevention (KCDC), which provided cross-sectional data designed to accurately evaluate the health and nutritional levels of the people. The analysis was conducted using eye examination data (last revised in March 2019).

The target group for the National Health and Nutrition Examination Survey is a cross-sectional survey designed to accurately assess the health and nutrition level of the people who live in Korea. All participants displayed accurate answers to the questions in the self-report questionnaire and filled out answers to the questionnaire indicating the amount of time exposed to sunlight per day to evaluate the subjects’ daily sunlight exposure time. Daily sunlight exposure times were compared and analyzed between those exposed for more than 2 h and less than 5 h and those exposed for more than 5 h.

To increase accuracy by extracting 192 sample spheres, the analysis was conducted on 952 subjects (522 males and 430 females) who were exposed to sunlight for more than 2 h. Subjects agreed to utilization of the analytical data of the questionnaire, and subjects who did not respond to the questionnaire or who did not have cataract disease were excluded from the analysis.

The survey can be summarized as follows:

• Age
• Check the sunlight exposure time during the day
  (1) 2 to 5 h; (2) More than 5 h; (3) No response
• Education level
  (1) Elementary-school graduation; (2) Middle-school graduation; (3) High-school graduation; (4) University graduation or higher
• Where you currently reside
  (1) Seoul; (2) Busan; (3) Daegu; (4) Incheon; (5) Gwangju; (6) Daejeon; (7) Ulsan; (8) Gyeonggi; (9) Gangwon; (10) Chungbuk; (11) Chungnam; (12) Jeonbuk; (13) Jeonnam; (14) Gyeongbuk; (15) Gyeongnam; (16) Jeju

The presence or absence of cataracts in participants was confirmed by an ophthalmologist through a slit lamp microscope, and cataracts were classified by type in the presence of cataracts.

Questionnaire (Slit Lamp Microscope)

• The presence or absence of cataracts
• Classification with cataracts
  (1) Cortical type; (2) Nuclear type; (3) Anterior subcapsular type; (4) Posterior subcapsular type; (5) Non-response (no examination)

2.2. Research Variables and Weight

In this study, the dependent variable was the incidence of cataracts, and the independent variable was the sunlight exposure time depending on the time of day, which was divided into a 2 to 5 h group and a 5 h or more group. Among the sampled households, all household members were selected for the survey, excluding unsuitable household members (living in other areas, etc.). Therefore, the household response rate was calculated as the percentage of households surveyed that completed the survey. The individual response rate was calculated as the percentage of survey respondents among surveyed households. The final response rate was calculated as the product of the household response rate and the household member response rate.

2.3. Statistical Analysis

In our study, we analyzed general characteristics by investigating sociological factors associated with sunlight exposure time and cataract prevalence in Korean adults. The analysis results presented percentages (%) and standard errors (S.E.) as a table and identified differences between 20 groups using the chi-square test. For analysis related to age among sociological factors, logistic regression analysis was performed to statistically verify its effect on cataracts. Statistical analysis was performed using SPSS version 26, and p < 0.05 was considered statistically significant.

For age-related analysis, a threshold was set based on the results of several previous studies based on the age of 45.

3. Results

To verify the difference in the ratio of cataract types according to the sunlight exposure time, a cross-tabulation was created. As a result, in the 2–5 h group, there were 52 cortical (30.1%), 115 nuclear (66.5%), 3 anterior subcapsular (1.7%), and 3 posterior subcapsular cataracts (1.7%), and in the 5 h or more group, there were 48 cortical (24.5%), 135 nuclear (68.9%), 10 anterior subcapsular (5.1%), and 3 posterior subcapsular cataracts (1.6%). As a result, both groups showed that nuclear cataracts were more prevalent in Koreans regardless of sunlight exposure time (p = 0.250) (

Table 1. Types of cataracts according to sunlight exposure time.

		Sun Exposure		Total	x2	p
		2–5 h	Over 5 h
Cataract	Cortical	52 (30.1)	48 (24.5)	100 (27.1)	4.112	0.250
	Nuclear	115 (66.5)	135 (68.9)	250 (67.8)
	Anterior subcapsular	3 (1.7)	10 (5.1)	13 (3.5)
	Posterior subcapsular	3 (1.7)	3 (1.6)	6 (1.6)
Total		173 (100)	196 (100)	369 (100)

Unit: Frequency (%).

).

Table 2. Sociodemographic analysis of study subjects. N = 952.

Division	Classification	Frequency	Ratio (%)
Sunlight	2–5 h	482	50.6
	Over 5 h	470	49.4
Gender	Male	522	54.8
	Female	430	45.2
Age	Over 45	259	27.2
	Under 45	693	72.8
Education Level (n = 896)	Elementary School	354	37.2
	Middle School	136	14.3
	High School	268	28.2
	University	138	14.5
Residence	Seoul	81	8.5
	Busan	92	9.7
	Daegu	90	9.5
	Incheon	38	4.0
	Gwangju	24	2.5
	Daejeon	13	1.4
	Ulsan	37	3.9
	Gyeonggi	139	14.6
	Gangwon	50	5.3
	Chungbuk	47	4.9
	Chungnam	21	2.2
	Jeonbuk	47	4.9
	Jeonnam	25	2.6
	Gyeongbuk	137	14.4
	Gyeongnam	96	10.1
	Jeju	15	1.6
Refractive Power (n = 869)	Myopia	303	−2.03 D (Std. E. 0.120)
	Hyperopia	566	1.31 D (Std. E. 0.042)

shows the demographic and sociological characteristics of the study subjects as follows. The amount of sunlight was 2–5 h in 482 people (50.6%), and more than 5 h in 470 people (49.4%), showing little difference in the proportions of the two groups. As for their gender, 522 (54.8%) were male and 430 (45.2%) were female, and 259 (27.2%) were under the age of 45 and 693 (72.8%) were over the age of 45. As for their educational level, 354 (37.2%) had graduated from elementary school and 136 (14.3%) from middle school. And there were 268 (28.2%) who had graduated from high school and 138 (14.5%) from university. Their residence data included 139 people in Gyeonggi Province (14.6%) and 137 in North Gyeongsang Province (14.4%), 15 in Jeju (1.6%), and 13 in Daejeon (1.4%). The refractive error was myopia in 303 patients (34.8%) and hyperopia in 566 patients (65.2%).

Cross-tabulations were calculated to verify differences in cataract incidence rates depending on sunlight exposure time. As a result, in the 2–5 h group, there were 275 people (57.1%) without cataracts and 207 people (42.9%) with cataracts. In the 5 h or more group, there were 213 people (45.3%) without cataracts, and the number of people with cataracts was 257 (54.7%). As a result of conducting a chi-square test to determine the statistical significance of the difference in the cataract incidence rate according to the sunlight exposure time, it was found that there was a statistically significant difference (Figure 1,

Table 3. Frequency of cataracts due to sunlight exposure.

		Sun Exposure		Total	x2	p
		2–5 h	Over 5 h
Prevalence of cataracts	Non.	275 (57.1)	213 (45.3)	488 (53.1)	13.116	<0.001 ***
	Exist.	207 (42.9)	257 (54.7)	464 (48.7)
Total		482 (100)	470 (100)	952 (100)

p *** < 0.001, Unit: Frequency (%).

).

Cross-tabulations were calculated to verify differences in cataract incidence rates by gender. As a result, in the 2–5 h group, there were 225 men (46.7%) and 257 women (53.3%), and in the 5 h or more group, there were 297 men (63.2%) and 173 women (36.8%). As a result of conducting a chi-square test to determine the statistical significance of the difference in cataract incidence rates between men and women according to the sunlight exposure time, the cataract incidence rate was 6.6% higher in women than men in the 2–5 h group, and in the group of more than 5 h, the rate in men was 26.4% higher than that in women, and this was statistically significant (Figure 2,

Table 4. Frequency of cataracts according to gender.

		Sun Exposure		Total	x2	p
		2–5 h	Over 5 h
Prevalence of cataract	Male	225 (46.7)	297 (63.2)	522 (100)	26.193	<0.001 **
	Female	257 (53.3)	173 (36.8)	430 (100)
Total		482 (100)	470 (100)	952 (100)

p ** < 0.01, Unit: Frequency (%).

).

To determine the difference in cataract incidence by sunlight exposure and age, a cross-analysis was conducted by dividing the subjects into groups of people over 45 years old and under 45 years old.

As a result, in the group exposed to sunlight for 2 to 5 h, 317 people (65.8%) were over 45 years old, and 165 people (34.2%) were under 45 years old. In the group exposed to sunlight for more than 5 h, 376 people (80.0%) were over 45 years old. Of these 376 people (80.0%), 94 people (20.0%) were under 45 years of age. A chi-square test was performed to determine whether the cataract incidence rate according to age was statistically significant. As a result, both the 2 to 5 h of sunlight exposure group and the 5 h or more of sunlight exposure group showed a statistically significantly higher incidence of cataracts after the age of 45 compared to before the age of 45 (Figure 3,

Table 5. Frequency of cataracts according to age.

0.001 **		Sun Exposure		Total	x2	p
		2–5 h	Over 5 h
Prevalence of cataract	Over 45	317 (65.8)	376 (80.0)	693 (72.8)	24.339	<0.001 ***
	Under 45	165 (34.2)	94 (20.0)	259 (27.2)
Total		482 (100)	470 (100)	952 (100)

p ** < 0.01, p *** < 0.001, Unit: Frequency (%).

).

Logistic regression analysis was performed to verify the effect of age on the occurrence of cataracts. As a result, the logistic regression model was found to be statistically significant (Hosmer and Lemeshow Test: x² = 8.872, p = 0.353), and the explanatory power of the regression model was approximately 60.5% (Nagelkerke R2 = 0.605). As a result of testing the significance of the regression coefficient, age (OR = 1.173, p < 0.001) was found to have a significant effect on the incidence of cataracts. It was estimated that age increases by about 1.173 times when it increases by one level (

Table 6. Increasing age affects the development of cataracts.

Dependent Variable	Independent Variable	B	S.E.	OR	95% CI	p
Prevalence	Age	0.160	0.010	1.173	(1.150~1.197)	<0.001

−2LL = 743.781, Nagelkerke R² = 0.605, Hosmer and Lemeshow Test: x² = 8.872 (p = 0.353).

).

Cross-tabulation analysis was conducted on 896 people (94.1%) out of a total of 952 people, excluding 56 people (5.9%) with missing data, to verify the difference in cataract incidence according to education level.

As a result, in terms of sunlight exposure of 2 to 5 h, there were 143 (31.4%) elementary-school graduates, 72 (15.4%) middle-school graduates, 147 (32.3%) high-school graduates, and 93 (20.4%) university graduates. And in the group of 5 h or more, 211 people graduated from elementary school (47.8%) graduated from middle school, 64 people (14.5%) graduated from high school, 212 people (27.4%) graduated from high school, and 45 people (10.2%) graduated from university.

As a result of conducting the chi-square test to find out the statistical significance of the cataract incidence rate due to the difference in the curriculum according to the exposure time of sunlight, the cataract incidence rate was higher for university graduates than for elementary-school graduates in the 2–5 h group. And in the group over 5 h, elementary-school graduates were higher than university graduates and were statistically significant. However, middle- and high-school graduates showed no significant difference between the 2–5 h group and the 5 h or more group (Figure 4,

Table 7. Frequency of cataracts according to education level.

		Sun Exposure		Total	x2	p
		2–5 h	Over 5 h
Prevalence of cataracts	Elementary school	143 (31.4)	211 (47.8)	354 (39.5)	32.540	<0.001 ***
	Middle school	72 (15.4)	64 (14.5)	136 (15.2)
	High school	147 (32.3)	212 (27.4)	268 (29.9)
	University	93 (20.4)	45 (10.2)	138 (15.4)
Total		455 (100)	441 (100)	896 (100)

p *** < 0.001, Unit: Frequency (%).

).

As shown in Figure 5, cross-tabulation analysis was performed to determine the differences in cataract incidence according to sunlight exposure and place of residence. As a result, in the group exposed to sunlight for 2 to 5 h, there were 52 people (10.8%) in the Seoul area and 63 people (13.1%) in the Busan area. In the group exposed to sunlight for more than 5 h, 36 people (7.7%) were in the Gangwon region and 85 people (18.1%) were in the Gyeongbuk region. A chi-square test was performed to determine the incidence of cataracts according to residential area. As a result, in the 2 to 5 h group, the cataract incidence rate was high in large cities such as Seoul and Busan, and in the 5 h or more group, the cataract incidence rate was significantly higher in rural areas such as Gangwon and Gyeongbuk.

In this analysis, the exposure time of sunlight in Koreans was significantly associated with increased cataract prevalence for over 5 h of exposure (54.7%).

In addition, the analysis of cataract prevalence according to the sunlight exposure time confirmed that the majority of Korean adults suffer from nuclear cataracts (67.8%). The 2–5 h group of sunlight exposure was found to be significantly associated with an increase in the cataract discrimination rate in women (53.3%), university graduates (20.4%), and those in urban areas (Seoul 10.8%, Busan 13.1%). On the other hand, in the group with more than 5 h of sunlight exposure, it was found that the cataract prevalence increased in men (63.2%), elementary-school graduates (47.8%), and those in rural areas (Gangwon 7.7%, Gyeongbuk 18.1%). However, the prevalence of cataracts significantly increased after age 45 in people with both 2–5 h and 5 h of sunlight exposure.

4. Discussion

In this study’s analysis of the difference in cataract prevalence according to the sunlight exposure and time, the proportion of subjects without cataracts in the 2–5 h sunlight exposure group was significantly higher than that of subjects with cataracts. On the other hand, in the 5 h or longer group, the proportion of subjects with cataracts was significantly higher than the proportion of subjects without cataracts. Therefore, in our study, we concluded that Korean adults are at risk of developing cataracts when the sunlight exposure time is more than 5 h. As in previous studies, it was suggested that sunlight exposure was related to cataracts for more than 5 h. An analysis of cataract prevalence according to the sunlight exposure time showed that the majority of Korean adults had nuclear cataracts (67.8%), followed by cortical cataracts (27.1%), posterior subcapsular cataracts (1.6%), and anterior subcapsular cataracts (3.5%). These results were similar to those reported by Xu L et al. [28].

Additionally, our study’s analysis of differences in cataract incidence by sunlight exposure and gender showed that, interestingly, men exposed to sunlight for more than 5 h had a higher incidence of cataracts. However, in the case of women, the incidence of cataracts was higher in the group exposed to sunlight for 2–5 h, so a temporal difference in the occurrence of cataracts according to gender could be confirmed. This time difference also suggests that women are more vulnerable to sunlight exposure than men when it comes to cataract prevalence. In a study analyzing the prevalence of cataracts in Koreans from 2008 to 2011, the prevalence of cataracts was higher in women (42.3%) than in men (38.9%), and this is partially consistent with previous studies that included causes of environmental exposure [29].

Tsai et al.’s analysis of 806 patients diagnosed with age-related cataracts found that women had a higher prevalence of cataracts than men (64.0% vs. 56.1%, p < 0.004). This involved nuclear cataracts (38.9%) being the most common type, followed by cortical cataracts (21.9%) and posterior subcapsular cataracts (9.2%) [30].

According to our study, the prevalence of cataracts in Koreans was in the following order: nuclear cataract (26.3%), cortical cataract (10.5%), and posterior subcapsular cataract (1.4%).

In Cruickshanks et al.’s study on ultraviolet light exposure and lens opacity, the relationship between sunlight exposure and the UV-B (ultraviolet-B) component of light and lens opacity was investigated. The results showed that men experiencing higher average annual UV-B light levels were 1.36-times more likely to have more severe cortical opacities than men experiencing lower average annual UV-B light levels [19].

In Kanthan’s study, age was the most important risk factor for cataracts, as in previous studies, and the incidence of senile cataracts was significantly higher in those aged over 49 compared to 40–49 years [31].

In our study, we performed statistical analysis for two groups around 45 years of age. The results showed that the incidence of cataracts from sunlight exposure was statistically more significantly higher in those over 45 years of age, and logistic regression analysis showed a 1.173-fold increase with age.

Geriatric cataracts are the most common type in adults, starting between the ages of 45 and 50 [32]. Aging is the most important risk factor for cataracts, as structural and functional changes in the lens can promote their development [33].

This result is partially consistent with the results of our study analyzing the difference in cataract incidence with sunlight exposure and age. The results showed that both the group exposed to sunlight for 2 to 5 h and the group exposed to sunlight for more than 5 h had a statistically significantly higher incidence of cataracts after the age of 45 compared to before the age of 45.

Various previous research results related to the level of education on cataracts show that a lower education level is associated with cortical cataracts and nuclear cataracts. Educational status may have a dependent relationship with socioeconomic status. However, it has actually been shown to be an independent risk factor for cataracts [34,35]. These authors also reported that socioeconomic status and educational status may present the possibility of more risk factors associated with common lifestyles that may create risk factors that have not yet been explained [34,35].

The results of our study’s analysis of differences in cataract incidence according to the sunlight exposure and education level showed that the incidence of cataracts was higher in university graduates than in elementary-school graduates when exposed to sunlight for 2 to 5 h. In the 5 h or more group, it was confirmed that elementary-school graduates had a higher incidence of cataracts than university graduates.

This means that in Korea, the higher the level of education, the more people work indoors, and the less time they are exposed to sunlight. However, the lower the level of education, the more work is performed outdoors than indoors. It is inferred that these workers will be more affected by sunlight exposure.

In addition, as a result of analyzing the difference in cataract incidence according to the sunlight exposure and place of residence, the cataract incidence rate was significantly higher in large cities such as Seoul and Busan in the 2–5 h group, and the incidence rate was significantly higher in rural areas such as Gangwon-do and Gyeongbuk in the 5 h or more group. It was very high. Therefore, it was confirmed that the prevalence of cataracts was higher in large cities despite shorter sunlight exposure times than in rural areas. This allows for a meaningful comparison of 4 out of 16 regions in Korea. It was confirmed that the prevalence of cataracts was higher even with shorter sunlight in highly urbanized areas among large cities than in two rural areas with very low urbanization among rural areas. Meanwhile, a study in Taiwan reported that participants living in highly urbanized areas had a higher prevalence of senile cataracts than those living in other levels of urbanization [36,37].

However, another study reported that the prevalence of cataracts was higher in rural areas than in urban areas in southern India, and that people living in rural areas were more likely to develop cataracts [38].

Through this study, it was confirmed that Koreans had a higher incidence of cataracts when exposed to sunlight for more than 5 h. In addition, when analyzing the prevalence of cataracts according to the sunlight exposure time by sociodemographic characteristics, different differences were found between cases where the sunlight exposure time was 2 to 5 h and cases where it was more than 5 h.

As a result of the analysis of factors affecting the prevalence of cataracts according to the sunlight exposure time, women had a high incidence of cataracts for 2 to 5 h of sunlight exposure, and men had a high incidence of cataracts for more than 5 h of sunlight exposure.

In addition, age-related differences were significantly higher after age 45 in both the 2 to 5 h sunlight exposure group and the 5 h sunlight exposure group. The difference in education level-related cataract prevalence was higher in university graduates in the 2 to 5 h sunlight exposure group, and higher in elementary-school graduates in the 5 h sunlight exposure group.

And in terms of regional differences, the incidence of cataracts was high in large cities for 2 to 5 h of sunlight exposure, and the incidence of cataracts was high in rural areas for more than 5 h of sunlight exposure. This means that people in urban areas are less likely to be exposed to sunlight because they spend a lot of time indoors, while those in rural areas outside the city are more likely to be exposed to sunlight than urban areas because there is a lot of outdoor activity. This can also be considered in relation to the results of the education-level analysis. It can be predicted that people with blue-collar jobs are engaged in outdoor, active jobs that expose them to more sunlight than those with white-collar jobs. This may be the reason for the high prevalence of cataracts.

Cataracts are the most common disease in ophthalmology, accounting for approximately 50% of blindness worldwide. In everyday life, exposure from sunlight UV rays is likely to damage the retina. Understanding trends in cataract prevalence worldwide over the past 30 years and into the future is critical for cataract control in key population groups.

However, population-based trend data from several Asian countries have not been fully reported; thus, more studies should be initiated in the future.

The limitation of this study is that the season was not included in the questionnaire. It is thought that future studies will analyze the possibility that exposure to sunlight in winter and exposure to sunlight in summer will have different effects on the eyes even if they are exposed for the same length of time.

Early identification of risk factors for cataracts and the investigation of risk factors related to cataract progression are reasonable from a public health perspective related to cataract progression. Beyond the current treatment approach, prevention aspects that can reduce the occurrence of cataracts in the future should be emphasized. Therefore, by providing basic data, it is hoped that this study will be used to realize the possibility of the early detection of ophthalmic cataracts through sophisticated biosensing methods that evaluate the biological information of living organisms [39].

In order to prevent cataracts, the habit of protecting the eye from the sunlight is essential in everyday life. On days when the sun is strong, it is important to protect the eyes by reducing outdoor activities during the day, and to wear a hat or sunscreen glasses or sunglasses during outdoor activities. In addition, cataracts should be detected early through regular ophthalmic examinations and vision should be preserved through appropriate treatment.

It was judged that protecting the eyes from sunlight UV rays is the first step in preventing cataracts and protecting precious vision.

5. Conclusions

This study examined the relationship between sunlight exposure time and cataract prevalence among Korean adults, drawing on data from the National Health and Nutrition Survey. The findings indicate that sunlight exposure of at least five hours is linked to a higher prevalence of cataracts, with various demographic factors influencing this association. Specifically, gender differences showed that women had a higher cataract incidence with 2–5 h of sunlight exposure, while men had an increased incidence at 5 h of exposure. Education level was also a factor, as college graduates showed a higher cataract prevalence with 2–5 h of sunlight exposure, whereas elementary-school graduates had increased prevalence with more than 5 h of exposure. Regional variations were observed, with urban areas experiencing a higher cataract prevalence at 2–5 h of sunlight exposure and rural areas showing higher prevalence when exposure exceeded 5 h. Age was another significant factor, with cataract prevalence rising sharply after age 45, regardless of exposure time. Therefore, this study highlights that the risk of cataracts is notably higher for individuals with prolonged (more than five hours) sunlight exposure, especially in rural areas with higher daylight exposure than urban settings. Given the growing environmental challenges, it is crucial to conduct further research to protect eye health against damage from ultraviolet exposure. Detailed studies on cataract risk factors are essential, and we hope that this research can serve as a foundation for future efforts in cataract prevention and eye health protection across the population.