Lens opacity prevalence among the residents in high natural background radiation area in Yangjiang, China.

The aim of the study was to evaluate the risk and threshold doses of lens opacity among residents exposed to low-dose radiation. Residents aged ≥45 years were recruited from a high natural background radiation (HNBR) area in Yangjiang City and a control area selected from nearby Enping City. Lens opacities (LOPs) were classified according to the Lens Opacities Classification System (LOCS) III system. Face-to-face interviews were conducted to collect information on lifestyles, migration and medical history. Life-time cumulative doses were estimated using gender, age, occupancy factors and environmental radiation doses received indoors and outdoors. Logistic regression analyses were conducted to estimate the dose response and determine thresholds. In the HNBR area, among 479 study participants, 101 (21.1%), 245(51.1%) and 23 cases (4.8%), respectively, of cortical, nuclear and posterior subcapsular (PSC) LOPs were found. In the control area, those types of LOPs were identified among 58 cases (12.6%), 206 cases (51.2%) and 6 cases (1.3%) of 462 examinees, respectively. Cumulative eye lens dose was estimated to be 189.5 ± 36.5 mGy in the HNBR area. Logistic analyses gave odds ratios at 100 mGy of 1.26 [95% confidence interval (CI) 1.00-1.60], 0.81 (95% CI 0.64-1.01) and 1.73 (95% CI 1.05-2.85) for cortical, nuclear and PSC LOPs, respectively. For cortical LOPs, a logistic analysis with a threshold dose gave a threshold estimate of 140 mGy (90% CI 110-160 mGy). The results indicated that population exposed to life-time, low-dose-rate environmental radiation was at an elevated risk of cortical and PSC LOPs. A statistically significant threshold dose was obtained for cortical LOPs and no threshold dose for PSC LOPs.