Myopia Mechanism

As myopia prevalence increases, researchers are trying to understand the factors and mechanisms affecting its development. With the protective effect of time spent outdoors well established, a multinational group of European investigators sought to explore associations between related measures of adult lifetime ultraviolet B (UVB) exposure and serum vitamin D3 levels, using data from more than 3,000 participants in the EUREYE cross-sectional population-based study. As reported at the 2016 annual meeting of the Association for Research in Vision and Ophthalmology (ARVO) in Seattle, USA, increased UVB exposure over adult life was associated with reduced odds of myopia, independent of years of education (adjusted odds ratio/OR of myopia = 0.72 per one standard deviation increase of UVB). And, the protective effect of UVB exposure was strongest in late adolescence and early adulthood. Although no association was found between serum vitamin D3 and myopia risk, an interaction between myopia, serum vitamin D3, and UVB was identified, such that there was an additive effect on myopia risk for varying serum vitamin D3 levels. Katie Williams FRCOphth, MRC Clinical Research Fellow, King’s College London, UK, presented the study. “Our findings support the idea that UVB and its close correlation with light levels may be one of the factors that contribute to the known beneficial effects of time spent outdoors, but the mechanism remains unclear, as we did not find evidence to support our hypothesis that it is mediated by increased vitamin D biosynthesis. The finding of an interaction between vitamin D and UVB, however, suggests vitamin D may still play a role through some yet to be identified pathway. Like many things in biology, the mechanisms by which various factors affect myopia development may be complicated,” she said. INVERSE RELATIONSHIP As an unexpected finding, the analyses showed that high plasma lutein was associated with a reduced risk of myopia. With subjects divided into quintiles based on plasma lutein level, those in the highest quintile had significantly reduced odds of myopia relative to those in the lowest quintile (OR = 0.57). Dr Williams noted that although plasma lutein has not been causally associated with myopia before, an inverse relationship has been reported between macular pigment optical density and axial length, and there is biologic plausibility for lutein to have a protective effect. “We could hypothesise that lutein provides neural protection through its antioxidant activity and thereby affects retinal signalling and scleral remodelling, both of which have been implicated in myopia development. Further research is warranted to explore an association between lutein and myopia,” she added. Katie Williams: Katie.williams@kcl.ac.uk

Tags: myopia, plasma lutein, UVB exposure