ABSTRACT
Objective To compare the early change of posterior corneal elevation with femtosecond laser assisted laser in situ keratomileusis (FS-LASIK) and sub-Bowman keratomileusis (SBK) by Oculyzer and analyze the related factors after FS-LASIK.Methods A longitudinal observational study was designed.Ninety-one eyes of 46 patients with myopia or myopic astigmatism in the First Affiliated Hospital of Anhui Medical University from January to April in 2016 were divided into FS-LASIK group (53 eyes of 27 patients),SBK group (38 eyes of 19 patients)according to the patients' wishes and each part of corneal elevation change values were explored after FS-LASIK and SBK surgeries.The posterior corneal elevation was measured at twenty-seven measuring points along the central,paracentral,midperipheral and peripheral zone (vertex and 1,2 and 3 mm radius) using Oculyzer preoperatively,l day,7 days and 1 month postoperatively,respectively.Written informed consent was obtained from each patient before the surgery.Results In the FS-LASIK group,the posterior corneal elevation difference values in the central zone were (-0.924± 1.859),(-1.151 ± 1.586) and (-0.940 ± 1.994) μm 1 day,7 days and 1 month postoperatively,respectively.In the periphery zone,the elevation difference values were (1.046 ± 1.667),(1.172 ± 1.566) and (1.023±1.622)μm.In the paracentral and midperipheral zone,the cornea displayed slightly backward or forward shift.In SBK group,the posterior corneal elevation difference values of the ve,ex were (-0.684 ± 1.454),(-1.053 ±1.723) and (-0.553 ± 1.572) μm 1 day,7 days and 1 month after operation,respectively.In the paracentral and midperipheral zone displayed the same trend with FS-LASIK group,and in the periphery,the values were (1.207 ±1.317),(1.327 ± 1.529) and (1.208 ± 1.415) μm.There were no statistically significant differences in posterior corneal elevation between the two surgery modes among the three time points (all at P ＞ O.05).At 1 month postoperatively,only two independent variables,which were spherical equivalent (SE) and ablation depth (AD)entered the regression in the central and paracentral zones.Independent variables,such as central thinnest corneal thickness (TCT),SE,AD,residual bed thickness (RBT) and the ratio of AD and TCT (AD/TCT) did not enter the regression in other two areas.Conclusions The posterior corneal elevation in the central 6 mm area shows tiny change in the early stage and the variation is larger 7 days after operation in the two groups,but it does not result in keratectasia.With the increase of SE and AD,the posterior corneal elevation is more likely to be affected.
ABSTRACT
<p><b>BACKGROUND</b>In March 2013, human cases of infection with a novel A (H7N9) influenza virus emerged in China. The epidemic spread quickly and as of 6 May 2013, there were 129 confirmed cases. The purpose of this study was to analyze the epidemiology of the confirmed cases, determine the impacts of bird migration and temperature changes on the H7N9 epidemic, predict the future trends of the epidemic, explore the response patterns of the government and propose preventive suggestions.</p><p><b>METHODS</b>The geographic, temporal and population distribution of all cases reported up to 6 May 2013 were described from available records. Risk assessment standard was established by analysing the temperature and relative humidity records during the period of extensive outbreak in three epidemic regions in eastern China, including Shanghai, Zhejiang and Jiangsu provinces. Risk assessment maps were created by combining the bird migration routes in eastern China with the monthly average temperatures from May 1993 to December 2012 nationwide.</p><p><b>RESULTS</b>Among the confirmed cases, there were more men than women, and 50.4% were elderly adults (age >61 years). The major demographic groups were retirees and farmers. The temperature on the days of disease onset was concentrated in the range of 9°C-19°C; we defined 9°C-19°C as the high-risk temperature range, 0°C-9°C or 19°C-25°C as medium risk and <0°C or >25°C as low risk. The relative humidity on the days of disease onset ranged widely from 25% to 99%, but did not correlate with the incidence of infection. Based on the temperature analysis and the eastern bird migration routes, we predicted that after May, the high-risk region would move to the northeast and inland, while after September, it would move back to north China.</p><p><b>CONCLUSIONS</b>Temperature and bird migration strongly influence the spread of the H7N9 virus. In order to control the H7N9 epidemic effectively, Chinese authorities should strengthen the surveillance of migrating birds, increase poultry and environmental sampling, improve live poultry selling and husbandry patterns and move from a "passive response pattern" to an "active response pattern" in focused preventive measures.</p>