The association between time spent outdoors and myopia using a novel biomarker of outdoor light exposure. 
We sought to determine whether conjunctival ultraviolet autofluorescence (UVAF), a biomarker of outdoor light exposure, is associated with myopia.  We performed a cross-sectional study on Norfolk Island and recruited individuals aged ≥ 15 years.  Participants completed a sun-exposure questionnaire and underwent non-cycloplegic autorefraction.  Conjunctival UVAF used a specially adapted electronic flash system fitted with UV-transmission filters (transmittance range 300-400 nm, peak 365 nm) as the excitation source.  Temporal and nasal conjunctival UVAF was measured in both eyes using computerized photographic analysis with the sum referred to as "total UVAF."  In 636 participants, prevalence of myopia decreased with an increasing quartile of total UVAF (P(trend) = 0.002).  Median total UVAF was lower in subjects with myopia (spherical equivalent [SE] ≤ -1.0 diopter [D]) than participants without myopia: 16.6 mm(2) versus 28.6 mm(2), P = 0.001.  In the multivariable model that adjusted for age, sex, smoking, cataract, height and weight, UVAF was independently associated with myopia (SE ≤ -1.0 D): odds ratio (OR) for total UVAF (per 10 mm(2)) was 0.81, 95% confidence interval (CI) 0.69 to 0.94, P = 0.007.  UVAF was also significantly associated with myopia when analysis was restricted to subjects <50 years, and in moderate-severe myopia (SE ≤ -3.0 D).  Prevalence of myopia decreased with increasing time outdoors (P(trend) = 0.03), but time outdoors was not associated with myopia on multivariable analysis.  Study authors identified a protective association between increasing UVAF and myopia.  The protective association of higher UVAF against myopia was stronger than that of increased levels of time spent outdoors as measured by this study's questionnaire.  Future studies should investigate the association between UVAF and incident myopia, and its relationship to myopic progression.