Effects of water level fluctuation on thermal stratification in a typical tributary bay of Three Gorges Reservoir, China.

Xiangxi River is a typical tributary of Three Gorges Reservoir (TGR) in China. Based on field observations in 2010, thermal stratification was significant in most months of the year. Through field data analysis and numerical simulations, the seasonal and spatial variation of thermal stratification as related to the impact of the operation of TGR were investigated. Thermal stratification was most pronounced from April to September in the Xiangxi River tributary. Air temperature (AT) and water level (WL) were the two dominant variables impacting thermal stratification. AT affected the surface water temperature promoting the formation of thermal stratification, and high WLs in TGR deepened the thermocline depth and thermocline bottom depth. These results provide a preliminary description of the seasonal variation and spatial distribution of thermal stratification, which is important for better understanding how thermal stratification affects algae blooms in Xiangxi River.

Housing type and myopia: the mediating role of parental myopia.

BACKGROUND: Myopia has become a significant global public health concern, and is highly prevalent worldwide especially in Asian countries. It is associated with genetic factors as well as socioeconomic status; however, the underlying cause for school myopia has not been established. This study evaluates the impact of living environment on school myopia in Chinese school-aged children. METHODS: A large cross-sectional sample of area- and ethnicity-matched school children; a total of 43, 771 children from 12 cities participated in this study. The presence of myopia was self-reported and potential risk factors were determined by questionnaires. RESULTS: The self-reported prevalence of myopia in Chinese children was 31.8 % (n = 13, 928). In multiple logistic regression analysis, higer risk of myopia among school-aged children was significantly positively associated with both parental myopia (OR = 3.57; 95 % CI: 3.26-3.90), living in 1-3 floor (OR = 1.28; 95 % CI: 2.57-3.15), 4-6 floor (OR = 1.84; 95 % CI: 1.73-1.95) and 7 floor or more (OR = 2.02; 95 % CI: 1.88-2.16). Particularly, housing type was independently associated with myopia after stratified by parental myopia. An increasing prevalence of myopia was found with increasing floor of housing type in each outdoor time group. CONCLUSIONS: Housing type was independently associated with myopia, after stratified by parental myopia. Flat room, lower living floor and more outdoor time may be protective factors for myopia among school-aged children in mainland China.

[Analysis on the time of sunshine exposure among Chinese primary and middle school students in 12 provinces].

OBJECTIVE: To investigate the characteristics on the time of sunshine exposure in Chinese primary and middle school students. METHODS: A total of 43 771 primary and middle school students were randomly selected from 12 provinces in China. A self-reported questionnaire was used to understand their time of sunshine exposure on weekdays and weekends as well as related family information and behaviors.χ(2) test was used to compare the hours of sunshine exposure among different groups. Multivariate logistic regression analysis was conducted to identify the influencing factors. RESULTS: Results from the current survey indicated that the average time of sunshine exposure on weekdays and weekends were 2.49 and 3.22 hours, respectively. On weekdays, proportions of students with time of sunshine exposure ≤2 h/d or >2 h/d were 60.81% and 39.19%, respectively. On weekends, the proportions became 44.05% and 55.95%, respectively. On weekdays, the time of sunshine exposure as ≤2 h/d was significantly different among factors as sex, urban or rural area, residential area, self-rating academic performance, type of housing or ways of commuting to school. On weekends, the time of sunshine exposure ≤2 h/d were significantly different among sex, residential areas, self-rating academic performance, type of housing and ways of commuting to school. Data from the multivariate logistic regression analysis showed that the limited sunshine exposure was significantly associated with factors as: type of primary schools, being girls, students living in the urban area or living in central or western areas, with normal or better academic performances, living in a flat apartment and the time spent on watching video program >2 h/d both on weekdays and weekends. CONCLUSION: The time of sunshine exposure seemed not enough among school students and significant differences were seen among different groups.

Effect of outdoor activity on myopia onset and progression in school-aged children in northeast China: the Sujiatun Eye Care Study.

BACKGROUND: Due to its high prevalence and associated sight-threatening pathologies, myopia has emerged as a major health issue in East Asia. The purpose was to test the impact on myopia development of a school-based intervention program aimed at increasing the time student spent outdoors. METHODS: A total of 3051 students of two primary (grades 1-5, aged 6-11) and two junior high schools (grades 7-8, aged 12-14) in both urban and rural Northeast China were enrolled. The intervention group (n = 1735) unlike the control group (n = 1316) was allowed two additional 20-min recess programs outside the classroom. A detailed questionnaire was administered to parents and children. Uncorrected visual acuity (UCVA) was measured using an E Standard Logarithm Vision Acuity Chart (GB11533-2011) at baseline, 6-month and 1-year intervals. A random subsample (n = 391) participated in the clinic visits and underwent cycloplegia at the beginning and after 1 year. RESULTS: The mean UCVA for the entire intervention group was significantly better than the entire control group after 1 year (P < 0.001). In the subgroup study, new onset of myopia and changes in refractive error towards myopia were direction during the study period was significantly lower in the intervention group than in the control group (3.70 % vs. 8.50 %, P = 0.048; -0.10 ± 0.65 D/year vs. -0.27 ± 0.52 D/year, P = 0.005). Changes in axial length and IOP were also significantly lower following the intervention group (0.16 ± 0.30 mm/year vs. 0.21 ± 0.21 mm/year, P = 0.034; -0.05 ± 2.78 mmHg/year vs. 0.67 ± 2.21 mmHg/year, P = 0.006). CONCLUSIONS: Increasing outdoor activities prevented myopia onset and development, as well as axial growth and elevated IOP in children. TRIAL REGISTRATION: Current controlled trials NCT02271373.

[Association between elevated light levels in classrooms and change in vision acuity among elementary and secondary students].

OBJECTIVES: To explore the association between elevated light levels in classrooms and change in vision acuity among elementary and secondary students. METHODS: A total of 4 elementary (grade 1-5) and secondary (grade 7-8) schools in urban and rural areas in Sujiatun, Shenyang, China were selected by cluster sampling as experimental schools, and lighting systems have been rebuilt to improve the ambient light levels in 56 classrooms in November 2012. The control schools were chosen for the comparable academic burden and adjacent location to experimental schools, 4 schools in all. Cluster sampling of all students in the selected schools as the subjects was carried out. A total of 2 092 students were chosen as experimental group and 1 595 students were in the control group. The luxmeter was used to measure illuminance of classrooms in two groups at baseline, and intervention for 1 month, respectively.Students in both groups were underwent 3 times for vision acuity examination by standard logarithmic visual acuity chart at baseline, intervention for 6 month and intervention for 1 year, respectively. The light levels of desk and blackboard in two groups were compared by Wilcoxon test. Multivariate analysis of covariance with repeated measures was performed to assess three vision acuity results between groups. RESULTS: After intervention, the average illuminance of desk (117.5 vs 532.5 lx, Z = -5.38, P < 0.001) and blackboard (75.6 vs 423.5 lx, Z = -5.38, P < 0.001) and uniformity of desk (Z = -4.28, P < 0.001) with new lighting were improved significantly than that with old lighting, however the uniformity of blackboard was lower than baseline significantly (0.64 vs 0.70, Z = -2.34, P = 0.019). The average scores of vision acuity in students at baseline, intervention for 6 month and intervention for 1 year were 4.87 ± 0.23, 4.84 ± 0.25 and 4.85 ± 0.23 in experimental group, and 4.88 ± 0.22, 4.84 ± 0.25 and 4.81 ± 0.27 in control group, respectively. The significant differences between groups were found and F values were 1.41, 0.13, 19.99, P values were 0.235,0.724, <0.001. At last the average vision acuity in experimental group were significantly better than that in control group either among elementary (4.90 ± 0.20) vs (4.87 ± 0.21) score, F = 13.61, P < 0.001 or secondary students (4.73 ± 0.28) vs (4.68 ± 0.32) score, F = 14.25, P < 0.001. CONCLUSIONS: Visual acuity loss could be decreased in students with elevated light levels which may slow the response to myopiagenic stimuli for eyes, therefore the ambient light levels of blackboard and desk in classroom should be improved.

Elevated light levels in schools have a protective effect on myopia.

PURPOSE: To determine whether elevated light levels in classrooms in rural areas can protect school-age children from myopia onset or myopia progression. METHODS: A total of 317 subjects from 1713 eligible students aged six to 14 in four schools located in northeast China participated in the study. Students received a comprehensive eye examination including cycloplegic refraction and ocular biometry, which included axial length (AL), anterior chamber depth (ACD), and corneal curvature (CC) measurement, and completed a questionnaire. The intervention arm included 178 students in two schools with rebuilt elevated lighting systems and the control arm included 139 students in which lighting systems were unchanged. Results for the two arms were compared with a Wilcoxon rank sum test, a chi-squared test or a t-test, as appropriate. Factors that might help explain any differences were explored with multivariate linear regression analysis. RESULTS: The median average illuminance of blackboards and desks and uniformity of desk lighting were significantly improved, however, the uniformity of blackboard lighting declined after intervention. At baseline, the mean refraction, AL, CC, ACD and myopia prevalence between the two arms were not significantly different. After 1 year, compared with the control arm the intervention arm had a lower incidence of new myopia onset (4% vs 10%; p = 0.029), a smaller decrease in refractive error among no myopic subjects (-0.25 dioptre [D] vs -0.47 D; p = 0.001), and shorter axial growth for both non-myopic (0.13 vs 0.18 mm; p = 0.023) and myopic subjects (0.20 vs 0.27 mm; p = 0.0001). Multivariate linear regression analysis showed the intervention program, lower hyperopic baseline refraction, lower father's education level, longer time sleeping and less time in screen-viewing activities were associated with less refractive shift in the direction of myopia in non-myopic children. For myopic subjects, myopia progression was significantly associated with family income only. The intervention program and older age had a protective effect on axial growth for both myopic and non-myopic subjects. The father's education level and sleep duration were significantly associated with axial growth in non-myopic children. CONCLUSIONS: Elevated light levels in classrooms have a significant effect on myopia onset, decreases in refraction, and axial growth; if the findings of lighting intervention are reproduced in future studies, the ambient light levels in schools should be improved.