Increased tear 8OHdG expression was identified consistently as a predictor of higher levels of tear HEL expression using univariate and multivariate models, and when using either transformed or raw data (
Table 2). This positive predictive relationship strongly suggested that lipid modification is accompanied by DNA modification on the ocular surface.
Univariate predictors for tear HEL expression demonstrate female sex, indoor occupation, spring season of collection, and contact lens wear may predict higher expression. Collectively these predictors support increased tear lipid peroxidation may be present in these subject groups when compared to male sex, outdoor occupation, winter season of collection, and no contact lens wear. However, when considering them together with the fact that univariate logistic regression demonstrated male sex predicted winter season of collection (P = 0.005), it is strongly suggested that the present study data were confounded by the fact that most samples collected from males and those with outdoor occupations were collected during the winter season. Furthermore, spring season of collection may have an influence on tear HEL expression directly through increased tear HEL expression and indirectly by possible increased release of cellular HEL into the tears. Subsequently, there is limited evidence in the present study to support the significance of sex, occupation, season of collection, and contact lens wear to tear HEL expression.
It was expected that increased levels of UV exposure would result in increased tear HEL expression; however, this hypothesis was not supported by the present data. Specifically, it was expected that those with outdoor occupations would have higher levels of tear HEL when compared to those with indoor occupations. Consequently, increased exposure to UV by those with outdoor occupations was expected to cause increased levels of lipid peroxidation. However, as reported previously, study subjects with outdoor occupations had only marginally higher hours of ocular sun exposure as they completed the study during the cold 2014 Ohio winter season.
9 This may explain why tear HEL expression was not increased in those with outdoor occupations. Alternatively, it was not surprising that sample collection in the spring season was associated with increased tear HEL expression. When compared to winter, ambient UV levels increase
30,31 along with outdoor activities during warmer seasons, potentially resulting in increased UV exposure.