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Charlotte M. McKnight, Seyhan Yazar, Justin Sherwin, Hannah Forward, Alex Tan, Terri L. Young, Christopher J. Hammond, Craig Pennell, Minas T. Coroneo, David A. Mackey; An Objective Biomarker Of Ocular Sun Exposure Is Inversely Correlated With Myopia In Young Adults: The Raine Eye Health Study. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2738.
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Several studies have demonstrated an inverse association between outdoor activity and myopia. Many of these studies have been limited by subjective measurement of outdoor activity, such as parental or participant recall via questionnaire. We used conjunctival ultraviolet autofluorescence photography, an objective, quantitative and reliable method of assessing ocular sun exposure, to investigate the relationship between outdoor activity, ultraviolet light exposure and myopia.
This was a cross-sectional study of 1231 young adults aged 19 to 22 years in the Raine cohort, Western Australia. Ultraviolet fluorescence images of the interpalpebral conjunctiva (right and left eye, nasal and temporal regions) were taken using a specially designed camera system. The images were digitally analysed, by one assessor, to calculate a total area of fluorescence in mm2 for each participant. Post-dilation refraction was measured using the Nidek ARK-510A autorefractor, with myopia defined as spherical equivalent less than -0.5 diopters. Parental history of myopia, time spent outdoors and educational activity were assessed by questionnaire.
Of the 1231 participants, 288 were myopic (23.4%). Median total conjunctival autofluorescence was lower in myopes than non-myopes (31.5mm2 vs 47.3mm2, p<0.001). Prevalence of myopia decreased with increasing quartiles of conjunctival autofluorescence, with 32.8% in the lowest quartile, 28.0% in the second quartile, 17.2% in the third quartile and 15.6% in the highest quartile. Participants in the lowest quartile had 2.6 times the odds of myopia than those in the highest quartile (95% confidence interval 1.7 to 3.8, p<0.001). The inverse association between myopia and conjunctival autofluorescence remained significant after adjustment for age, gender, time outdoors, educational activity and parental history of myopia (OR 2.5, 95% confidence interval 1.5 to 4.2, p<0.001).
We have shown a significant inverse correlation between myopia and objectively measured ocular sun exposure in young adults. These findings have implications for our understanding of myopia pathogenesis, of particular importance given the increasing prevalence of myopia worldwide. As causality cannot be inferred given the cross-sectional design of this study, prospective studies looking at conjunctival autofluorescence and development of myopia are required.
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