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L. T. Chylack, Jr., A. H. Feiveson, W. H. Tung, L. E. Peterson, M. L. Wear, L. J. Marak, F. A. Cucinotta; Nasca Study: Results of Longitudinal Five-Year Study. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2511.
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© ARVO (1962-2015); The Authors (2016-present)
NASCA is designed to measure the impact of exposure to space radiation on progression rates of cortical (C), nuclear (N), and posterior subcapsular opacification (P) in US astronauts (Ast) who have flown at least one mission in space (AstEx), astronauts who have not flown in space (Ast0Ex), and military aircrew (Mil). The study is complete; we present our analyses of 5-6 years of data.
All subjects had eye exams at NASA. Digital lens images (Nidek EAS 1000) were obtained. Nutritional data were derived from standardized questionnaires. Because of high variability and skewness of opacity measures, nonparametric methods were used to test for association between rates of opacification and space radiation exposure. First, median regression was used to obtain robust estimates of slopes of opacity vs. time for each eye of each subject. Next, a partial correlation analogue of Kendall's Tau was used to quantify and test radiation effect on slopes, adjusting for confounding variables age, nutritional and sun-exposure histories, with std. errors adjusted for repeated observations on each eye for each subject. Exposure of lens to space radiation was estimated using recorded personal dosimetry from each space mission, adjusted by radiation quality factor, and quantified in terms of dose equivalent and dose equivalent latency for total & galactic cosmic radiation. For Ast0Ex and Mil radiation exposure was set = zero. In addition to the analysis of growth rates, we similarly analyzed median values of max (OD,OS) opacity over the multiple visits for each subject.
The follow-up intervals for Ast were: 5 yr 171; 4 yr 189; 3 yr 199; 2 yr 202; 1 yr 225. For Mil intervals were: 5 yr 56; 4 yr: 73; 3 yr 81; 2 yrs 90; 1 yr 96. Partial tau analyses showed for C there was statistically significant adverse effect (p=0.033) of exposure (yes/no) on C progression. Also for C using a skew-normal cross-sectional model on log "% area opaque" for C collapsed to median for each subject, variance was higher in AstEx. For N using nonparametric cross-sectional analyses on collapsed (to medians) maximum opacity (over 2 eyes) within an oval mask and at specific loci an adverse effect with exposure (p=0.02) was found. We found no relationship between exposure and P. Higher saturated fat intake was associated with deleterious effects on C, N, and P.
Exposure to space radiation accelerates C opacification and may worsen N opacification, but not P opacification. The adverse effect on C appears greater the larger the C opacity at the time of exposure.
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