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L. T. Chylack, Jr., L. E. Peterson, A. H. Feiveson, M. L. Wear, F. K. Manuel, W. H. Tung, L. J. Marak, D. Hardy, F. A. Cucinotta; NASCA Report 1: Study of Relationship of Exposure to Space Radiation and Risk of Lens Opacity - Baseline Data. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2268.
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The NASA Study of Cataract in Astronauts (NASCA) is a 5-yr investigation of lens opacification in U.S. astronauts and two exposure control groups with and without a history of military aviation, respectively. Goals are to determine the effect of space radiation exposure on the severity + progression of age-related cortical (C), nuclear (N), and posterior subcapsular (PSC) opacities.
170 consenting astronauts or ex-astronauts who had flown at least 1 mission in space and 3 control groups, a) 54 astronauts who had not yet flown in space, b) 90 military aircrew or ex-aircrew personnel, and c) 97 non-aircrew ground-based controls were recruited from the local occupational aerospace community. Continuous measures of severity of C, N, and PSC were derived from Nidek EAS 1000 digitized images. Age, demographics, general health, nutritional intake, solar ocular exposure, and other confounding variables were measured at baseline. Astronauts who flew at least one mission were matched to an equal number of control subjects using propensity scores based on demographic characteristics and medical history, stratified by gender and smoking (ever/never). For the 1st year of the study, the cross-sectional data for matched subjects were analyzed by fitting customized non-normal regression models to examine the effect of space radiation on each measure of opacity, adjusting for gender, age, nutrient intake, and group category (astronaut, aircrew, ground-based).
Exposed astronauts were mostly older than those who had not yet flown in space, however after adjusting for age differences with a skew-normal regression model, both the variability and median of cortical opacity were significantly higher for exposed astronauts than they would have been for a hypothetical group of non-exposed astronauts with similar ages (P = 0.015). No statistical evidence was found linking space radiation with increased area of PSC opacity or with increased nuclear pixel density.
Analysis of cross-sectional data revealed a small deleterious effect of space radiation for cortical opacity. However the effect within individuals might be magnified through passage of time. Analysis of longitudinal data from the remaining study years will help address this conjecture and might also identify changes in nuclear or PSC opacity as subjects age.
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