The global prevalence of visual impairment (VI) is a significant public health concern, particularly in light of the aging population. VI refers to the functional limitations of the eye or visual system resulting from various eye diseases, including cataracts, uncorrected refractive errors, glaucoma, age-related macular degeneration (AMD), and diabetic retinopathy (DR) (1, 2). As reported by the World Health Organization (WHO), at least 2.2 billion people were blind or visually impaired worldwide in 2019 (3). It is estimated that by 2050, the number of individuals with moderate to severe VI globally will increase from 216.6 million in 2015 to 587.6 million (4). Visual-related functional burden (VRFB) is used to describe an individual's ability to perform everyday visual tasks in real-world conditions (5). VI has been associated with disabilities in activities of daily living such as reading, household tasks, and driving (6, 7). Previous studies have reported that VI is associated with many chronic diseases, such as chronic kidney disease, type 2 diabetes, sleep disorders, and depressive symptoms (5, 7–9). Seriously, VI can lead to restricted physical activity, significant financial costs, and reduced life expectancy (1, 10).

The human eye, a highly specialized organ of vision, is significantly influenced by oxidants of endogenous and exogenous origin, such as ultraviolet radiation, diseases, aging, environmental pollutants, and other factors (11, 12). Oxidative stress results from an imbalance between the production of reactive oxidative species (ROS) and the body's antioxidant defense system (13). It has the potential to damage tissues, resulting in alterations to tissue structure and function, increased vascular permeability, microvascular abnormalities, and neovascularization. Consequently, these alterations can result in the development of corneal, conjunctival, and optic neuropathy; lens crystallin degeneration; elevated intraocular pressure; and retinal degeneration (14). It represents a significant contributing factor in the pathogenesis of ocular diseases, including AMD, DR, dry eye disease (DED), glaucoma, and cataracts (15–19). Dietary nutrition and lifestyle play a critical role in ocular health. Available evidence suggests that several dietary components, such as vitamins A, B, C, E, carotenoids and magnesium, and lifestyle factors, such as smoking and physical activity, may modulate oxidative stress in AMD and DR (20–22). Collectively, these findings emphasize the critical involvement of oxidative stress in the pathogenesis of ocular diseases. The oxidative balance score (OBS), as a valuable tool for comprehensively measuring oxidative stress-related exposures, incorporates both lifestyle and dietary factors to assess an individual's oxidative balance status (23). The initial OBS was developed by Van Hoydonck et al. and comprises solely three components: two antioxidants (β-carotene and vitamin C) and one pro-oxidant factor (iron) (24). Subsequently, over 20 adaptations of these OBSs have been extensively utilized in epidemiological studies to assess the correlations between oxidative status and the risk of developing chronic diseases (25).

In the field of ophthalmology, previous studies have primarily focused on the mechanisms of occurrence between oxidative stress and specific ocular diseases (11). A recent study has reported a relationship between OBS and DR, with results suggesting that higher OBS is associated with a lower risk of DR (20). However, there is a paucity of epidemiologic evidence on the relationship between OBS and functional vision. In the present study, we collected two consecutive cycles of the National Health and Nutrition Examination Survey (NHANES) data from 2005 to 2008 (2005–2006 and 2007–2008). Our study aims to fill this gap by investigating the relationship between OBS and VRFB and to provide new insights into maintaining eye health in American adults.

In this national, multiracial, cross-sectional study of 6,682 participants in the United States, a negative correlation was found between OBS and VRFB among adults aged 20 years and older. This is consistent with previous studies in DR populations (20). Notably, an L-shaped association was observed between OBS and VRFB. Subgroup analyses demonstrated that this phenomenon was particularly prevalent among the employed population. Furthermore, the sensitivity analyses provided further evidence to support the robustness of the results.

In this study, the OBS incorporates both pro-oxidant and antioxidant factors, as well as lifestyle and dietary variables, to assess an individual's oxidative balance status. Pro-oxidant factors can induce oxidative stress through the generation of ROS or by reducing antioxidant defense activity. In contrast, antioxidant factors have the potential to shift the balance toward a less pro-oxidant state (30). Notable antioxidant factors include dietary antioxidants, maintaining a healthy weight, refraining from smoking, engaging in regular physical activity, and abstaining from alcohol consumption (31).

The VRFB showed differences for OBS components (Supplementary Table 5). In addition, we further explored the association between each component of OBS, dietary OBS, lifestyle OBS, and VRFB (Supplementary Tables 6–8, and Supplementary Figures 2, 3). A cross-sectional study across multiple regions has demonstrated that nutrients are of paramount importance in maintaining vision health (21). Essential vitamins including A, C, E, and beta-carotene, in conjunction with enzyme systems localized within various cellular compartments—including mitochondria, peroxisomes, and the cytosol—work synergistically with key minerals such as selenium, copper, and zinc to support the eye's defense mechanisms against oxidative stress and promote overall ocular health (12, 32). A diet that is rich in antioxidants is of great importance to support these innate defense systems. Vitamin C, as a potent antioxidant, plays a crucial role in ocular physiology and the prevention of eye diseases (33). It protects ocular structures, such as the lens and cornea, from oxidative damage, thereby enhancing antioxidant defenses. A meta-analysis revealed a significant association between lower levels of vitamin C and DR (34). Vitamin E has been demonstrated to combat free radicals, prevent lipid oxidation, and maintain cell membrane integrity, while also serving to shield retinal ganglion cells from oxidative stress (35, 36). It also reduces the risk of cataracts by protecting the lens of the eye from oxidative damage (37). Additionally, Vitamin E contributes to the antioxidant defenses of the ocular surface, potentially benefiting patients with DED (38). The AREDS also indicated that 5 years after the end of the clinical trial, the beneficial effects of the antioxidants C, E, β-carotene, and/or zinc on the development of AMD persisted (38). The vitamin B complex plays a critical role in maintaining overall eye health and reducing the risk of diseases such as cataracts and glaucoma (39). In this study, the dietary OBS components include vitamins B2, B3, B6, and B12, which possess antioxidant properties and promote neuronal survival and regeneration (40). The AREDS found a negative correlation between increased intake of B2 and B12 and the incidence of cataracts (41). The available evidence suggests that antioxidant vitamin and mineral supplements may have the potential to slow the progression of AMD (42).

Beyond dietary factors, it is important to consider the impact of lifestyle on functional vision. Obesity is a risk factor for most potentially blinding eye diseases, such as glaucoma, cataracts, AMD, and DR (43, 44). Inflammation and oxidative stress play significant role in the relationship between obesity and ocular diseases (45). Sedentary behavior increases the risk of dry eye symptoms, particularly in individuals with low levels of physical activity (46). A higher level of physical activity is associated with a reduced incidence of cataracts due to a reduction in oxidative damage (43). Animal research indicated that aerobic exercise may safeguard photoreceptor cells and retinal pigment epithelium from harm and prevent thinning of the retinal and photoreceptor layers in a mouse model of retinal degeneration (47). Smoking and alcohol consumption lower antioxidant levels in the body, leading to additional oxidative damage (48). One study found that rats exposed to cigarette smoke exhibited damage to the cornea and lacrimal glands, which may be related to ROS-induced DNA oxidation (49). Several studies have revealed that alcohol consumption is associated with primary open-angle glaucoma, DR, and AMD (50, 51).

In the subgroup analyses, we identified a significant interaction between employment status and the relationship between OBS and VRFB. Notably, the protective effect of OBS was more pronounced among the unemployed, suggesting a potential modifying influence of OBS within this group. This interaction has important implications for understanding how different subgroups may benefit differently from interventions aimed at preventing functional vision loss. Similar studies have indicated that individuals with lower socioeconomic status tend to have poorer dietary and lifestyle habits, as well as a higher prevalence of eye diseases (52, 53). Therefore, it is crucial to strengthen health education and promote lifestyle improvements, particularly for those with lower socioeconomic status.

The present study has several strengths that enhance the validity and reliability of the findings. First, the utilization of data from the nationally representative survey NHANES permits the results to be generalized to a more expansive US population. The weighted analysis guarantees that the resulting estimates are representative of the entire population and takes into account the complex survey design. Furthermore, the OBS incorporates both antioxidants and pro-oxidants, integrating dietary and lifestyle variables for a more comprehensive assessment of individual antioxidant status. Secondly, the restricted cubic spline analysis offered valuable insights into the non-linear association between the OBS and VRFB. A further strength of this study is the sensitivity analysis, which assesses the stability of the results.

However, some limitations to this study should be recognized. First, this cross-sectional study provides valuable insights into the association between OBS and VRFB; however, it faces limitations in causal inference. For instance, the presence of chronic vision problems may result in a decline in quality of life, which, in turn, could contribute to the development of oxidative stress. Consequently, the necessity for additional longitudinal studies is evident in order to establish the causal relationship between these two variables. Second, VRFB was assessed by answering six questions on functional visual impairment, which could have introduced subjective bias in assessment. Future studies should use objective measurement methods to assess visual function, as this would enhance the reliability of the research. Third, the 24-h dietary recall method used to collect dietary data may introduce recall bias, as it relies on the participants' ability to accurately remember and report their food intake. Future studies could improve the accuracy of dietary recall data by utilizing multiple 24-h recall periods and incorporating other validation methods. Fourth, potential confounding factors such as screen use duration, other disease histories, and medication histories were not fully considered, and overlooking these factors could introduce bias in interpreting the relationship. It is recommended that more prospective studies explore these factors in more detail to improve the accuracy and generalizability of the results. Fifth, a further limitation of OBS is that it is unable to measure endogenous antioxidant or pro-oxidant function. Moreover, our analyses are based on the assumption that the impact of pro- and antioxidant exposures is equally weighted, which may not accurately reflect the actual contribution of each exposure. Finally, the data utilized in this study were derived from the NHANES between 2005 to 2008. The release of an updated version of the NHANES questionnaire on functional vision is eagerly anticipated. In future studies, it is necessary to adopt a longitudinal follow-up research design to explore the association between oxidative balance status and functional vision. The core assessment framework includes two major dimensions: (1) oxidative balance status indicators, which are measured using biomarkers such as plasma total antioxidant capacity and glutathione peroxidase activity; and (2) visual function assessment indicators, encompassing high-contrast visual acuity and contrast sensitivity function.

In conclusion, we found an L-shaped relationship between OBS and VRFB among U.S. adults aged 20 years and older, where higher antioxidant exposure, as measured by the OBS, was associated with a reduced risk of VRFB. This novel finding suggests that maintaining a favorable oxidative balance through modifiable dietary and lifestyle (such as increased physical activity, smoking cessation, reduced alcohol consumption) may help protect functional vision. We also observed a stronger negative association between OBS and VRFB among the unemployed. This study provides new insights into the prevention of functional vision loss, highlighting the importance of not only dietary and lifestyle factors but also considering different subgroups, such as the unemployed. Further longitudinal studies are required to further validate these observations and elucidate the underlying mechanisms, particularly in elucidating causal relationships among variables, controlling for confounding factors, and examining the development of visual function.